Tathamay Basu - Profile on Academia.edu (original) (raw)
Papers by Tathamay Basu
Journal of Materials Chemistry C, 2018
Low dimensional magnetic systems (such as spin-chain) are extensively studied due to their exotic... more Low dimensional magnetic systems (such as spin-chain) are extensively studied due to their exotic magnetic properties. Here, we would like to address that such systems should also be interesting in the field of dielectric, ferroelectricity and magnetodielectric coupling. As a prototype example, we have investigated a one-dimensional (1D) helical-chain metal-organic hybrid system with a chiral structure which shows a broad hump in magnetic susceptibility around 55 K (T max). The complex dielectric constant exactly traces this feature, which suggests intrinsic magnetodielectric coupling in this chiral system. The dipolar ordering at T max occurs due to lattice-distortion which helps to minimize the magnetic energy accompanied by 1D-magnetic ordering or vice-versa. This experimental demonstration initiates a step to design and investigate hybrid organic-inorganic magnetic systems consisting of chiral structure towards ferroelectricity and magnetodielectric coupling. Low dimensional magnetic systems, such as, spin-chain, spin-ladder, single molecule magnets, have received considerable interest in the past years because they exhibit many fascinating phenomena due to the presence of exotic magnetism, such as spin-gap, spin-Peierls instability and slow relaxation of the magnetization. 1-5 Tremendous research has been performed in both organic and inorganic systems from the magnetism point of view, however, those materials could be equally important in the field of dielectric, ferroelectricity, piezoelectricity, multiferroicity and magnetodielectric coupling. Ferroelectricity was demonstrated in a chargetransfer salt tetrathiafulvalene-p-bromanil, a probable one-dimensional organic quantum magnet, where it is evident that spin-Peierls instability plays an important role to generate ferroelectricity. 6 An electric dipole driven magnetism was also documented in a charge-transfer organic salt, where long range magnetic and ferroelectric ordering is stabilized via loss of magnetic frustration. 7 Recently, it has been speculated that low dimensional magnetism could also favor magnetodielectric coupling, which is one of the current hot topics in the field of solid state physics and material science, through investigation of some spin-chain oxide systems. 8-11 The magnetic instability often helps lattice distortion to minimize the total ground state energy, so that multiferroicity/magnetodielectric coupling arises in those systems. Eventually, among those few available reports in organic/inorganic systems, a direct one-to-one correlation between magnetism and dielectric in a low-dimensional (spin-chain) system was practically demonstrated only in the geometrically frustrated spin-chain oxide Ca 3 Co 2 O 6 , by documenting a clear broad hump in temperature dependent magnetic susceptibility and dielectric constant. 9,10 Apart from pure organic/inorganic materials, another recent promising approach is to design multiferroic/magnetodielectric hybrid organic-inorganic frameworks (HOIF), where one
Advanced quantum technologies, Nov 9, 2020
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires 1 Multiferroics BaCoX2O7 (X = P, As) compounds with incommensurate structural waves but collinear spins ingredients.
一軸異方性スピンクラスタガラスFe 2 ちO 5 におけるマルチガラス特性と磁気電気結合
Physical Review B, 2014
Magnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5
AIP Advances, Mar 1, 2015
Dielectric and magnetodielectric behavior of polycrystalline Ca3CoRhO6, a geometrically frustrated magnetic system
Nucleation and Atmospheric Aerosols, 2015
We have investigated dielectric andmagnetodielectric properties of the geometrically frustrated s... more We have investigated dielectric andmagnetodielectric properties of the geometrically frustrated spin -chain compound Ca3CoRhO6, which is known to undergo ‘partially disordered antiferromagnetic’ transition around 90 K (T1) followed by another glassy magnetic transition around 30 K (T2). We have observed dielectric glass behavior around 90 K, at the magnetic transition, which indicates that this behavior is predominantly magnetic in its origin. The magnetic field dependent dielectric constant in the magnetically ordered state tracks the features in isothermal magnetization thereby establishingmagnetodielectric coupling in this compound.
Physical Review Materials, Nov 2, 2020
We report detailed magnetic, transport, heat-capacity, and neutron diffraction measurements of Ba... more We report detailed magnetic, transport, heat-capacity, and neutron diffraction measurements of Ba5Ru3O12, a compound consisting of isolated Ru3O12 trimers. We show that this system develops long-range antiferromagnetic ordering at TN ~ 60 K without structural distortion or metal-insulator-type transition, which is in sharp contrast to other Barium Ruthenate trimer systems such as 9R-BaRuO3 and Ba4Ru3O10. A complex magnetic structure is revealed which is attributable to the magnetic frustration due to competing exchange interactions between Ru ions on different crystallographic sites within the Ru3O12 trimer and different degree of orbital hybridization on different Ru-sites. We have also investigated the magnetic structure of Ba4Ru3O10 for comparisons. I.
Journal of Magnetism and Magnetic Materials, Nov 1, 2018
The compound EuPd2Si2 is a well-known fluctuating-valent compound with a largest variation of Eu ... more The compound EuPd2Si2 is a well-known fluctuating-valent compound with a largest variation of Eu valence in a narrow temperature interval (around 150 K). The ball-milled form of this compound was investigated to understand the Eu valence behavior in the nanoform. The compound is found to retain the ThCr2Si2-type tetragonal structure after ball-milling leading to a reduction in particle size, typically falling in the range 10-100 nm. We find that there is a qualitative change in the temperature dependence of magnetic susceptibility for such small particles, with respect to that known for bulk form. To understand this microscopically, Mössbauer spectra as a function of temperature were taken. The Mössbauer spectrum of the nanocrystalline compound is essentially divalent-like at room temperature, but becomes distinctly bimodal at all temperatures below 300 K, unlike that of the bulk form. That is, there is a progressive transfer of intensity from divalent position to trivalent position with a gradual decrease of temperature. We attribute it to a first-order valence transition, with extreme broadening by defects in the nano specimen. Thus there is a qualitative change in the valence behavior in this compound as the particle size is reduced by ball-milling. Such a particle size study is reported for the first time for a Eu-based mixed valent compound.
Robust nature of frustrated antiferromagnetism in ACrO[sub 2](A = Pd∕Li) compounds
Nucleation and Atmospheric Aerosols, 2013
ABSTRACT Geometrically frustrated (GF) delafossite systems PdCrO2 and LiCrO2 have received some a... more ABSTRACT Geometrically frustrated (GF) delafossite systems PdCrO2 and LiCrO2 have received some attention in recent years because of their interesting physical phenomena and also from the application point of view. Metallic PdCrO2 and insulating LiCrO2, consisting of layered triangular arrangement of Cr+3, exhibits antiferromagnetic nature with two dimensional (2D) frustration. Recent studies reveal the presence of the spin correlation in a wide temperature range well above magnetic ordering temperature TN. It is of interest to investigate whether the frustration can be released by the application of external pressure or magnetic field in metallic and insulating environment in this structure. We have carried out magnetization under external hydrostatic pressure (up to 10 kbar) and heat capacity under high magnetic field of 140 kOe on these systems. The result reveals robust nature of the frustrated antiferromagnetic system irrespective of whether compound is metallic or insulating.
Observation of spin glass-like behavior in fine particles of Nd2PdSi3
SOLID STATE PHYSICS: Proceedings of the 56th DAE Solid State Physics Symposium 2011, 2012
ABSTRACT We have investigated the magnetic behavior of ball-milled fine particles of an anomalous... more ABSTRACT We have investigated the magnetic behavior of ball-milled fine particles of an anomalous magnetic compound Nd2PdSi3 through magnetization and heat capacity measurements. It was observed that the magnetic ordering is broadened and transition temperature is marginally reduced in the fine particles. Our results reveal that, with the decrease in particle size, spin glass-like behavior is observed in this compound.
Magnetodielectric properties of frustrated antiferromagnet LiCrO[sub 2]
SOLID STATE PHYSICS: PROCEEDINGS OF THE 57TH DAE SOLID STATE PHYSICS SYMPOSIUM 2012, 2013
ABSTRACT We have investigated the magnetic, thermodynamic and dielectric properties of two dimens... more ABSTRACT We have investigated the magnetic, thermodynamic and dielectric properties of two dimensional spin frustrated Heisenberg antiferromagnet LiCrO2, TN =62K. The combined studies of dc magnetization, heat capacity and dielectric measurements confirm the coupling between electric and magnetic order parameters. Extensive in-field dielectric measurements as a function of magnetic field provide evidence for linear magnetodielectric effect near TN.
Physical review, Oct 17, 2019
The rare-earth based ternary intermetallic compounds R2T X3 (R = rare-earth, T = transitionmetal,... more The rare-earth based ternary intermetallic compounds R2T X3 (R = rare-earth, T = transitionmetal, X = Si, Ge, Ga, In) have attracted considerable interest due to a wide range of interesting low temperature properties. Here we investigate the magnetic state of Nd2PdSi3 using neutron diffraction, muon spin relaxation (µSR) and inelastic neutron scattering (INS). This compound appears anomalous among the R2PdSi3 series, since it was proposed to order ferromagnetically, whereas others in this series are antiferromagnets. Although some members of the R2T X3 series have been reported to form ordered superstructures, our data are well described by Nd2PdSi3 adopting the AlB2-type structure with a single Nd site, and we do not find evidence for superlattice peaks in neutron diffraction. Our results confirm the onset of long range magnetic order below T0 = 17 K, where the whole sample enters the ordered state. Neutron diffraction measurements establish the presence of a ferromagnetic component in this compound, as well as an antiferromagnetic one which has a propagation vector k2 = (1/2, 1/2, 1/4 − δ) with a temperature dependent δ ≈ 0.02 − 0.04, and moments orientated exclusively along the c-axis. µSR measurements suggest that these components coexist on a microscopic level, and therefore the magnetic structure of Nd2PdSi3 is predominantly ferromagnetic, with a sinusoidally modulated antiferromagnetic contribution which reaches a maximum amplitude at 11 K, and becomes smaller upon further decreasing the temperature. INS results show the presence of crystalline-electric field (CEF) excitations above T0, and from our analysis we propose a CEF level scheme.
Journal of Physics: Condensed Matter, Nov 12, 2013
We have systematically investigated the influence of gradual replacement of Ca by Gd on the magne... more We have systematically investigated the influence of gradual replacement of Ca by Gd on the magnetic and complex dielectric properties of the well-known geometrically frustrated spin-chain system, Ca 3 Co 2 O 6 (T N = 24 K with additional magnetic transitions below 12K), by studying the series, Ca 3-x Gd x Co 2 O 6 (x ≤ 0.7), down to 1.8K. Heat capacity measurements establish that the reduction of T N with Gd substitution is much less as compared to that by Y substitution. The magnetic moment data reveal that there are changes in the oxidation state of Co as well, unlike for Y-substitution, beyond x= 0.2. Thus, despite being isovalent, both these substitutions interestingly differ in changing these magnetic properties in these oxides. We propose that the valence electrons of Y and those of R ions play different roles on deciding these magnetic characteristics of these mixed oxides. It is observed that a small amount (x= 0.3) of Gd substitution for Ca is enough to suppress glassy ac magnetic susceptibility behavior for the peak around 12 K. An additional low-temperature magnetic anomaly close to 5 K gets more prominent with increasing Gd concentration as revealed by heat-capacity data. Trends in temperature dependence of complex dielectric behavior were also tracked with varying composition and a frequency dependence is observed, not only for the transition in the region around 10 K (for some compositions), but also for the 5 K transition which is well-resolved for a higher concentration of Gd. Thus, Gd-substituted Ca 3 Co 2 O 6 series is shown to reveal interesting magnetic and dielectric behavior of this family of oxides.
arXiv (Cornell University), Sep 22, 2019
In the series R2PdSi3, Nd2PdSi3 is an anomalous compound in the sense that it exhibits ferromagne... more In the series R2PdSi3, Nd2PdSi3 is an anomalous compound in the sense that it exhibits ferromagnetic order unlike other members in this family. The magnetic ordering temperature is also unusually high compared to the expected value for a Nd-based system, assuming 4f localization. Here, we have studied the electronic structure of single crystalline Nd2PdSi3 employing high resolution photoemission spectroscopy and ab initio band structure calculations. Theoretical results obtained for the effective electron correlation strength of 6 eV corroborate well with the experimental valence band spectra. While there is significant Pd 4d-Nd 4f hybridization, the states near the Fermi level are found to be dominated by hybridized Nd 4f-Si 3p states. Nd 3d core level spectrum exhibits multiple features manifesting strong final state effects due to electron correlation, charge transfer and collective excitations. These results serve as one of the rare demonstrations of hybridization of Nd 4f states with the conduction electrons possibly responsible for the exoticity of this compound.
arXiv (Cornell University), Mar 11, 2015
We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE) behaviour of a Hald... more We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE) behaviour of a Haldane spin-chain compound containing light rare-earth ion, Nd 2 BaNiO 5 , in detail, as a function of temperature (T) and magnetic field (H) down to 2 K. In addition to the well-known long range antiferromagnetic order setting in at (T N =) 48 K as indicated in dc magnetization (M), we have observed another magnetic transition near 10 K; this transition appears to be of a glassy-type which vanishes with a marginal application of external magnetic field (even H= 100 Oe). There are corresponding anomalies in dielectric constant (ɛ') as well with variation of T. The isothermal M(H) curves at 2 and 5 K reveal the existence of a magnetic-field induced transition around 90 kOe; the isothermal ɛ'(H) also tracks such a metamagnetic transition. These results illustrate the MDE coupling in this compound. Additionally, we observe a strong frequency dependence of a step in ɛ'(T) with this feature appearing around 25-30 K for the lowest frequency of 1 kHz, far below T N. This is attributed to interplay between crystal-field effect and exchange interaction between Nd and Ni, which establishes the sensitivity of dielectric measurements to detect such effects. Interestingly enough, the observed dispersions of the ɛ'(T) curves is essentially H-independent in the entire Trange of measurement, despite the existence of MDE coupling, which is in sharp contrast with other heavy rare-earth members in this series.
マルチフェロイックDyFe0.5Cr0.5O3における正孔ドーピングによる磁気秩序温度と磁気誘電結合の増加
Journal of Physics: Condensed Matter, 2017
Physical Review Materials, Nov 1, 2019
The role of rare-earth (R) ions on the magnetodielectric (MD) coupling is always intriguing and m... more The role of rare-earth (R) ions on the magnetodielectric (MD) coupling is always intriguing and markedly different for different systems. Although many reports are available concerning this aspect in frustrated 3dtransition metal oxides, no such reports exist on higher d (4d/5d)-orbital based systems due to the rare availability of highly insulating 4d/5d-systems. Here, we systematically investigated the magnetic, dielectric, ferroelectric and magnetodielectric behavior of the 6H-perovskites Ba3RRu2O9 for different R-ions, namely, R= Sm, Tb and Ho, which magnetically order at 12, 9.5 and 10.2 K respectively. For R=Tb and Ho, the temperature and magnetic-field dependent complex dielectric constant traces the magnetic features, which manifests MD coupling in this system. A weak magnetic-field (H) induced transition is observed for ~30 kOe, which is clearly captured in H-dependent dielectric measurements. No MD coupling is observed for Ba3SmRu2O9. The MD coupling is enhanced by a factor of 3 and 20 times for R=Tb and Ho, respectively, when compared to that of the Nd-counterpart. These results evidence the gradual enhancement of MD coupling with the introduction of heavier R-ions in this series, which is attributed to their larger moment values. Our investigation establishes dominating 4d(Ru)-4f(R) magnetic correlation in this series for the heavier R-members.
Journal of Physics: Condensed Matter, Jan 6, 2017
We report the results of our investigations of magnetic, thermodynamic and dielectric properties ... more We report the results of our investigations of magnetic, thermodynamic and dielectric properties of Ca substituted half-doped orthochromite, Dy 0.6 Ca 0.4 Fe 0.5 Cr 0.5 O 3. Magnetic susceptibility and heat capacity data bring out that this compound undergoes two antiferromagnetic transitions, one at ~ 132 and other at ~ 22 K. These values are higher than those of DyFe 0.5 Cr 0.5 O 3. This finding highlights that non-magnetic hole doping in form of Ca +2 , in the place of magnetic Dy +3 , tends to enhance magnetic transition temperatures in this half-doped orthochromite. We attribute it to possible change in the valence state of Cr/Fe-ion ions due to hole doping. Dielectric anomalies are also seen near the magnetic ordering temperatures indicating magnetodielectric coupling, which is confirmed by magnetic field dependent dielectric studies. The most notable observation is that magnetodielectric coupling strength gets significantly enhanced as compared to DyFe 0.5 Cr 0.5 O 3. The results reveal that it is possible to tune magnetoelectric coupling by hole doping in this system.
![Research paper thumbnail of Erratum: “Implications of magnetic and magnetodielectric behavior of GdCrTiO<sub>5</sub>” [J. Appl. Phys. <b>118</b>, 234103 (2015)]](https://attachments.academia-assets.com/106635748/thumbnails/1.jpg)
](Journal of Applied Physics, May 14, 2017
Physical Review B, Nov 14, 2011
Among the members of the series R 2 PdSi 3 (R= Rare-earths), the magnetic behavior of Nd compound... more Among the members of the series R 2 PdSi 3 (R= Rare-earths), the magnetic behavior of Nd compound is interesting in some respects. This compound is considered to order ferromagnetically (below 16 K), unlike other members of this series which order antiferromagnetically. In addition, magnetic ordering temperature (T o) is significantly enhanced with respect to de Gennes scaled value. In order to understand the magnetism of this compound better, we have investigated the magnetic behavior in detail (under external pressure as well) and also of its solid solutions based on substitutions at Nd and at Si sites, viz., on the series, Nd 2x (Y, La) x PdSi 3-y Ge y (x, y = 0.2, 0.4, 0.8, and 1.2) by bulk measurements. The results overall establish that Nd 2 PdSi 3 orders ferromagnetically below 16 K, but antiferromagnetic component seems to set in at very low temperatures. Notably, there is a significant suppression of T 0 for Y and Ge substitutions, compared to La substitution, for a given magnitude of unit-cell volume change, however qualitatively correlating with the separation between the layers of Nd and Pd-Si(Ge). On the basis of this observation, we conclude that 4f(Nd) hybridization plays a major role on the magnetism of the former solid solutions. To our knowledge, this work serves as a rare demonstration of 4f-hybridization effects on the magnetism of an Nd-based intermetallic compound.
Applied Physics Letters, Sep 8, 2014
We have investigated the magnetic, dielectric and magnetodielectric (MDE) behavior of a geometric... more We have investigated the magnetic, dielectric and magnetodielectric (MDE) behavior of a geometrically frustrated spin-chain system, Ca 3 Co 1.4 Rh 0.6 O 6 , in the single crystalline form for different orientations. The results bring out that the magnetic behavior of this compound is by itself interesting in the sense that this compound exhibits an anisotropic glassy-like magnetic behavior with a huge frequency () dependence of ac susceptibility (χ) peak for an orientation along the spin-chain in the range 30-60 K; this behavior is robust to applications of large external magnetic fields (H) unlike in canonical spin-glasses. The temperature dependence of dielectric constant also shows strong -dependence with similar robustness to H. The isothermal H-dependent dielectric results at low temperatures establishes anisotropic MDE coupling. It is intriguing to note that there is a 'step' roughly at one-third of saturation values as in the case of isothermal magnetization curves for same temperatures (for orientation along spin-chain), a correlation hitherto unrealized for geometrically frustrated systems.
Journal of Materials Chemistry C, 2018
Low dimensional magnetic systems (such as spin-chain) are extensively studied due to their exotic... more Low dimensional magnetic systems (such as spin-chain) are extensively studied due to their exotic magnetic properties. Here, we would like to address that such systems should also be interesting in the field of dielectric, ferroelectricity and magnetodielectric coupling. As a prototype example, we have investigated a one-dimensional (1D) helical-chain metal-organic hybrid system with a chiral structure which shows a broad hump in magnetic susceptibility around 55 K (T max). The complex dielectric constant exactly traces this feature, which suggests intrinsic magnetodielectric coupling in this chiral system. The dipolar ordering at T max occurs due to lattice-distortion which helps to minimize the magnetic energy accompanied by 1D-magnetic ordering or vice-versa. This experimental demonstration initiates a step to design and investigate hybrid organic-inorganic magnetic systems consisting of chiral structure towards ferroelectricity and magnetodielectric coupling. Low dimensional magnetic systems, such as, spin-chain, spin-ladder, single molecule magnets, have received considerable interest in the past years because they exhibit many fascinating phenomena due to the presence of exotic magnetism, such as spin-gap, spin-Peierls instability and slow relaxation of the magnetization. 1-5 Tremendous research has been performed in both organic and inorganic systems from the magnetism point of view, however, those materials could be equally important in the field of dielectric, ferroelectricity, piezoelectricity, multiferroicity and magnetodielectric coupling. Ferroelectricity was demonstrated in a chargetransfer salt tetrathiafulvalene-p-bromanil, a probable one-dimensional organic quantum magnet, where it is evident that spin-Peierls instability plays an important role to generate ferroelectricity. 6 An electric dipole driven magnetism was also documented in a charge-transfer organic salt, where long range magnetic and ferroelectric ordering is stabilized via loss of magnetic frustration. 7 Recently, it has been speculated that low dimensional magnetism could also favor magnetodielectric coupling, which is one of the current hot topics in the field of solid state physics and material science, through investigation of some spin-chain oxide systems. 8-11 The magnetic instability often helps lattice distortion to minimize the total ground state energy, so that multiferroicity/magnetodielectric coupling arises in those systems. Eventually, among those few available reports in organic/inorganic systems, a direct one-to-one correlation between magnetism and dielectric in a low-dimensional (spin-chain) system was practically demonstrated only in the geometrically frustrated spin-chain oxide Ca 3 Co 2 O 6 , by documenting a clear broad hump in temperature dependent magnetic susceptibility and dielectric constant. 9,10 Apart from pure organic/inorganic materials, another recent promising approach is to design multiferroic/magnetodielectric hybrid organic-inorganic frameworks (HOIF), where one
Advanced quantum technologies, Nov 9, 2020
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires 1 Multiferroics BaCoX2O7 (X = P, As) compounds with incommensurate structural waves but collinear spins ingredients.
一軸異方性スピンクラスタガラスFe 2 ちO 5 におけるマルチガラス特性と磁気電気結合
Physical Review B, 2014
Magnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5
AIP Advances, Mar 1, 2015
Dielectric and magnetodielectric behavior of polycrystalline Ca3CoRhO6, a geometrically frustrated magnetic system
Nucleation and Atmospheric Aerosols, 2015
We have investigated dielectric andmagnetodielectric properties of the geometrically frustrated s... more We have investigated dielectric andmagnetodielectric properties of the geometrically frustrated spin -chain compound Ca3CoRhO6, which is known to undergo ‘partially disordered antiferromagnetic’ transition around 90 K (T1) followed by another glassy magnetic transition around 30 K (T2). We have observed dielectric glass behavior around 90 K, at the magnetic transition, which indicates that this behavior is predominantly magnetic in its origin. The magnetic field dependent dielectric constant in the magnetically ordered state tracks the features in isothermal magnetization thereby establishingmagnetodielectric coupling in this compound.
Physical Review Materials, Nov 2, 2020
We report detailed magnetic, transport, heat-capacity, and neutron diffraction measurements of Ba... more We report detailed magnetic, transport, heat-capacity, and neutron diffraction measurements of Ba5Ru3O12, a compound consisting of isolated Ru3O12 trimers. We show that this system develops long-range antiferromagnetic ordering at TN ~ 60 K without structural distortion or metal-insulator-type transition, which is in sharp contrast to other Barium Ruthenate trimer systems such as 9R-BaRuO3 and Ba4Ru3O10. A complex magnetic structure is revealed which is attributable to the magnetic frustration due to competing exchange interactions between Ru ions on different crystallographic sites within the Ru3O12 trimer and different degree of orbital hybridization on different Ru-sites. We have also investigated the magnetic structure of Ba4Ru3O10 for comparisons. I.
Journal of Magnetism and Magnetic Materials, Nov 1, 2018
The compound EuPd2Si2 is a well-known fluctuating-valent compound with a largest variation of Eu ... more The compound EuPd2Si2 is a well-known fluctuating-valent compound with a largest variation of Eu valence in a narrow temperature interval (around 150 K). The ball-milled form of this compound was investigated to understand the Eu valence behavior in the nanoform. The compound is found to retain the ThCr2Si2-type tetragonal structure after ball-milling leading to a reduction in particle size, typically falling in the range 10-100 nm. We find that there is a qualitative change in the temperature dependence of magnetic susceptibility for such small particles, with respect to that known for bulk form. To understand this microscopically, Mössbauer spectra as a function of temperature were taken. The Mössbauer spectrum of the nanocrystalline compound is essentially divalent-like at room temperature, but becomes distinctly bimodal at all temperatures below 300 K, unlike that of the bulk form. That is, there is a progressive transfer of intensity from divalent position to trivalent position with a gradual decrease of temperature. We attribute it to a first-order valence transition, with extreme broadening by defects in the nano specimen. Thus there is a qualitative change in the valence behavior in this compound as the particle size is reduced by ball-milling. Such a particle size study is reported for the first time for a Eu-based mixed valent compound.
Robust nature of frustrated antiferromagnetism in ACrO[sub 2](A = Pd∕Li) compounds
Nucleation and Atmospheric Aerosols, 2013
ABSTRACT Geometrically frustrated (GF) delafossite systems PdCrO2 and LiCrO2 have received some a... more ABSTRACT Geometrically frustrated (GF) delafossite systems PdCrO2 and LiCrO2 have received some attention in recent years because of their interesting physical phenomena and also from the application point of view. Metallic PdCrO2 and insulating LiCrO2, consisting of layered triangular arrangement of Cr+3, exhibits antiferromagnetic nature with two dimensional (2D) frustration. Recent studies reveal the presence of the spin correlation in a wide temperature range well above magnetic ordering temperature TN. It is of interest to investigate whether the frustration can be released by the application of external pressure or magnetic field in metallic and insulating environment in this structure. We have carried out magnetization under external hydrostatic pressure (up to 10 kbar) and heat capacity under high magnetic field of 140 kOe on these systems. The result reveals robust nature of the frustrated antiferromagnetic system irrespective of whether compound is metallic or insulating.
Observation of spin glass-like behavior in fine particles of Nd2PdSi3
SOLID STATE PHYSICS: Proceedings of the 56th DAE Solid State Physics Symposium 2011, 2012
ABSTRACT We have investigated the magnetic behavior of ball-milled fine particles of an anomalous... more ABSTRACT We have investigated the magnetic behavior of ball-milled fine particles of an anomalous magnetic compound Nd2PdSi3 through magnetization and heat capacity measurements. It was observed that the magnetic ordering is broadened and transition temperature is marginally reduced in the fine particles. Our results reveal that, with the decrease in particle size, spin glass-like behavior is observed in this compound.
Magnetodielectric properties of frustrated antiferromagnet LiCrO[sub 2]
SOLID STATE PHYSICS: PROCEEDINGS OF THE 57TH DAE SOLID STATE PHYSICS SYMPOSIUM 2012, 2013
ABSTRACT We have investigated the magnetic, thermodynamic and dielectric properties of two dimens... more ABSTRACT We have investigated the magnetic, thermodynamic and dielectric properties of two dimensional spin frustrated Heisenberg antiferromagnet LiCrO2, TN =62K. The combined studies of dc magnetization, heat capacity and dielectric measurements confirm the coupling between electric and magnetic order parameters. Extensive in-field dielectric measurements as a function of magnetic field provide evidence for linear magnetodielectric effect near TN.
Physical review, Oct 17, 2019
The rare-earth based ternary intermetallic compounds R2T X3 (R = rare-earth, T = transitionmetal,... more The rare-earth based ternary intermetallic compounds R2T X3 (R = rare-earth, T = transitionmetal, X = Si, Ge, Ga, In) have attracted considerable interest due to a wide range of interesting low temperature properties. Here we investigate the magnetic state of Nd2PdSi3 using neutron diffraction, muon spin relaxation (µSR) and inelastic neutron scattering (INS). This compound appears anomalous among the R2PdSi3 series, since it was proposed to order ferromagnetically, whereas others in this series are antiferromagnets. Although some members of the R2T X3 series have been reported to form ordered superstructures, our data are well described by Nd2PdSi3 adopting the AlB2-type structure with a single Nd site, and we do not find evidence for superlattice peaks in neutron diffraction. Our results confirm the onset of long range magnetic order below T0 = 17 K, where the whole sample enters the ordered state. Neutron diffraction measurements establish the presence of a ferromagnetic component in this compound, as well as an antiferromagnetic one which has a propagation vector k2 = (1/2, 1/2, 1/4 − δ) with a temperature dependent δ ≈ 0.02 − 0.04, and moments orientated exclusively along the c-axis. µSR measurements suggest that these components coexist on a microscopic level, and therefore the magnetic structure of Nd2PdSi3 is predominantly ferromagnetic, with a sinusoidally modulated antiferromagnetic contribution which reaches a maximum amplitude at 11 K, and becomes smaller upon further decreasing the temperature. INS results show the presence of crystalline-electric field (CEF) excitations above T0, and from our analysis we propose a CEF level scheme.
Journal of Physics: Condensed Matter, Nov 12, 2013
We have systematically investigated the influence of gradual replacement of Ca by Gd on the magne... more We have systematically investigated the influence of gradual replacement of Ca by Gd on the magnetic and complex dielectric properties of the well-known geometrically frustrated spin-chain system, Ca 3 Co 2 O 6 (T N = 24 K with additional magnetic transitions below 12K), by studying the series, Ca 3-x Gd x Co 2 O 6 (x ≤ 0.7), down to 1.8K. Heat capacity measurements establish that the reduction of T N with Gd substitution is much less as compared to that by Y substitution. The magnetic moment data reveal that there are changes in the oxidation state of Co as well, unlike for Y-substitution, beyond x= 0.2. Thus, despite being isovalent, both these substitutions interestingly differ in changing these magnetic properties in these oxides. We propose that the valence electrons of Y and those of R ions play different roles on deciding these magnetic characteristics of these mixed oxides. It is observed that a small amount (x= 0.3) of Gd substitution for Ca is enough to suppress glassy ac magnetic susceptibility behavior for the peak around 12 K. An additional low-temperature magnetic anomaly close to 5 K gets more prominent with increasing Gd concentration as revealed by heat-capacity data. Trends in temperature dependence of complex dielectric behavior were also tracked with varying composition and a frequency dependence is observed, not only for the transition in the region around 10 K (for some compositions), but also for the 5 K transition which is well-resolved for a higher concentration of Gd. Thus, Gd-substituted Ca 3 Co 2 O 6 series is shown to reveal interesting magnetic and dielectric behavior of this family of oxides.
arXiv (Cornell University), Sep 22, 2019
In the series R2PdSi3, Nd2PdSi3 is an anomalous compound in the sense that it exhibits ferromagne... more In the series R2PdSi3, Nd2PdSi3 is an anomalous compound in the sense that it exhibits ferromagnetic order unlike other members in this family. The magnetic ordering temperature is also unusually high compared to the expected value for a Nd-based system, assuming 4f localization. Here, we have studied the electronic structure of single crystalline Nd2PdSi3 employing high resolution photoemission spectroscopy and ab initio band structure calculations. Theoretical results obtained for the effective electron correlation strength of 6 eV corroborate well with the experimental valence band spectra. While there is significant Pd 4d-Nd 4f hybridization, the states near the Fermi level are found to be dominated by hybridized Nd 4f-Si 3p states. Nd 3d core level spectrum exhibits multiple features manifesting strong final state effects due to electron correlation, charge transfer and collective excitations. These results serve as one of the rare demonstrations of hybridization of Nd 4f states with the conduction electrons possibly responsible for the exoticity of this compound.
arXiv (Cornell University), Mar 11, 2015
We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE) behaviour of a Hald... more We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE) behaviour of a Haldane spin-chain compound containing light rare-earth ion, Nd 2 BaNiO 5 , in detail, as a function of temperature (T) and magnetic field (H) down to 2 K. In addition to the well-known long range antiferromagnetic order setting in at (T N =) 48 K as indicated in dc magnetization (M), we have observed another magnetic transition near 10 K; this transition appears to be of a glassy-type which vanishes with a marginal application of external magnetic field (even H= 100 Oe). There are corresponding anomalies in dielectric constant (ɛ') as well with variation of T. The isothermal M(H) curves at 2 and 5 K reveal the existence of a magnetic-field induced transition around 90 kOe; the isothermal ɛ'(H) also tracks such a metamagnetic transition. These results illustrate the MDE coupling in this compound. Additionally, we observe a strong frequency dependence of a step in ɛ'(T) with this feature appearing around 25-30 K for the lowest frequency of 1 kHz, far below T N. This is attributed to interplay between crystal-field effect and exchange interaction between Nd and Ni, which establishes the sensitivity of dielectric measurements to detect such effects. Interestingly enough, the observed dispersions of the ɛ'(T) curves is essentially H-independent in the entire Trange of measurement, despite the existence of MDE coupling, which is in sharp contrast with other heavy rare-earth members in this series.
マルチフェロイックDyFe0.5Cr0.5O3における正孔ドーピングによる磁気秩序温度と磁気誘電結合の増加
Journal of Physics: Condensed Matter, 2017
Physical Review Materials, Nov 1, 2019
The role of rare-earth (R) ions on the magnetodielectric (MD) coupling is always intriguing and m... more The role of rare-earth (R) ions on the magnetodielectric (MD) coupling is always intriguing and markedly different for different systems. Although many reports are available concerning this aspect in frustrated 3dtransition metal oxides, no such reports exist on higher d (4d/5d)-orbital based systems due to the rare availability of highly insulating 4d/5d-systems. Here, we systematically investigated the magnetic, dielectric, ferroelectric and magnetodielectric behavior of the 6H-perovskites Ba3RRu2O9 for different R-ions, namely, R= Sm, Tb and Ho, which magnetically order at 12, 9.5 and 10.2 K respectively. For R=Tb and Ho, the temperature and magnetic-field dependent complex dielectric constant traces the magnetic features, which manifests MD coupling in this system. A weak magnetic-field (H) induced transition is observed for ~30 kOe, which is clearly captured in H-dependent dielectric measurements. No MD coupling is observed for Ba3SmRu2O9. The MD coupling is enhanced by a factor of 3 and 20 times for R=Tb and Ho, respectively, when compared to that of the Nd-counterpart. These results evidence the gradual enhancement of MD coupling with the introduction of heavier R-ions in this series, which is attributed to their larger moment values. Our investigation establishes dominating 4d(Ru)-4f(R) magnetic correlation in this series for the heavier R-members.
Journal of Physics: Condensed Matter, Jan 6, 2017
We report the results of our investigations of magnetic, thermodynamic and dielectric properties ... more We report the results of our investigations of magnetic, thermodynamic and dielectric properties of Ca substituted half-doped orthochromite, Dy 0.6 Ca 0.4 Fe 0.5 Cr 0.5 O 3. Magnetic susceptibility and heat capacity data bring out that this compound undergoes two antiferromagnetic transitions, one at ~ 132 and other at ~ 22 K. These values are higher than those of DyFe 0.5 Cr 0.5 O 3. This finding highlights that non-magnetic hole doping in form of Ca +2 , in the place of magnetic Dy +3 , tends to enhance magnetic transition temperatures in this half-doped orthochromite. We attribute it to possible change in the valence state of Cr/Fe-ion ions due to hole doping. Dielectric anomalies are also seen near the magnetic ordering temperatures indicating magnetodielectric coupling, which is confirmed by magnetic field dependent dielectric studies. The most notable observation is that magnetodielectric coupling strength gets significantly enhanced as compared to DyFe 0.5 Cr 0.5 O 3. The results reveal that it is possible to tune magnetoelectric coupling by hole doping in this system.
Journal of Applied Physics, May 14, 2017
Physical Review B, Nov 14, 2011
Among the members of the series R 2 PdSi 3 (R= Rare-earths), the magnetic behavior of Nd compound... more Among the members of the series R 2 PdSi 3 (R= Rare-earths), the magnetic behavior of Nd compound is interesting in some respects. This compound is considered to order ferromagnetically (below 16 K), unlike other members of this series which order antiferromagnetically. In addition, magnetic ordering temperature (T o) is significantly enhanced with respect to de Gennes scaled value. In order to understand the magnetism of this compound better, we have investigated the magnetic behavior in detail (under external pressure as well) and also of its solid solutions based on substitutions at Nd and at Si sites, viz., on the series, Nd 2x (Y, La) x PdSi 3-y Ge y (x, y = 0.2, 0.4, 0.8, and 1.2) by bulk measurements. The results overall establish that Nd 2 PdSi 3 orders ferromagnetically below 16 K, but antiferromagnetic component seems to set in at very low temperatures. Notably, there is a significant suppression of T 0 for Y and Ge substitutions, compared to La substitution, for a given magnitude of unit-cell volume change, however qualitatively correlating with the separation between the layers of Nd and Pd-Si(Ge). On the basis of this observation, we conclude that 4f(Nd) hybridization plays a major role on the magnetism of the former solid solutions. To our knowledge, this work serves as a rare demonstration of 4f-hybridization effects on the magnetism of an Nd-based intermetallic compound.
Applied Physics Letters, Sep 8, 2014
We have investigated the magnetic, dielectric and magnetodielectric (MDE) behavior of a geometric... more We have investigated the magnetic, dielectric and magnetodielectric (MDE) behavior of a geometrically frustrated spin-chain system, Ca 3 Co 1.4 Rh 0.6 O 6 , in the single crystalline form for different orientations. The results bring out that the magnetic behavior of this compound is by itself interesting in the sense that this compound exhibits an anisotropic glassy-like magnetic behavior with a huge frequency () dependence of ac susceptibility (χ) peak for an orientation along the spin-chain in the range 30-60 K; this behavior is robust to applications of large external magnetic fields (H) unlike in canonical spin-glasses. The temperature dependence of dielectric constant also shows strong -dependence with similar robustness to H. The isothermal H-dependent dielectric results at low temperatures establishes anisotropic MDE coupling. It is intriguing to note that there is a 'step' roughly at one-third of saturation values as in the case of isothermal magnetization curves for same temperatures (for orientation along spin-chain), a correlation hitherto unrealized for geometrically frustrated systems.