Athinarayanan Sundaresan | Jawaharlal Nehru Centre for Advanced Scientific Research (original) (raw)
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Papers by Athinarayanan Sundaresan
EPL (Europhysics Letters), 2011
APL Materials, 2020
Combining ferroelectricity and magnetism in the same material remains a challenge because it invo... more Combining ferroelectricity and magnetism in the same material remains a challenge because it involves complex crystal chemistry and stringent symmetry requirements. In conventional ferroelectrics, the polarization arises from the second-order Jahn–Teller effect associated with cations of d0 or s2 lone pair electronic configuration. In contrast, the magnetism arises from cations with partially filled d or f electrons. Materials that incorporate these two kinds of cations in different crystallographic sites exhibit multiferroic properties but with weak coupling between magnetism and ferroelectricity. On the other hand, a strong cross-coupling occurs in some materials, where specific spin structures induce weak ferroelectricity below the magnetic ordering temperature. In this article, we discuss a new class of multiferroics where the polar distortion results from chemical ordering. These polar oxides are mainly pyroelectric in the entire temperature range and exhibit magnetoelectric co...
Physical Review B, 1997
Magnetic and magnetoresistance measurements were carried out on a distorted perovskite, Eu 0.58 S... more Magnetic and magnetoresistance measurements were carried out on a distorted perovskite, Eu 0.58 Sr 0.42 MnO 3. In the absence of applied magnetic field, this compound is an insulator down to 5 K. Results of the ac-and dc-susceptibility measurements suggest a spin-glass ground state. An applied field of 7 T drives the insulator ground state to a ferromagnetic metallic state below T C ϭ120 K. For a range of intermediate fields, the compound undergoes insulator-metal-insulator transitions which resemble those of 1:1 Mn 3ϩ /Mn 4ϩ charge-ordered compounds. A temperature-field phase diagram is established which depicts different magnetic and electronic states. ͓S0163-1829͑97͒06109-2͔ PHYSICAL REVIEW B
Journal of Materials Chemistry, 1996
The European Physical Journal B, 2000
ABSTRACT : Neutron and electron diffraction, electrical transport and magnetic measurements have ... more ABSTRACT : Neutron and electron diffraction, electrical transport and magnetic measurements have been carried out on a newly synthesized electron doped Sr1-xCe x MnO3 (x = 0.1, 0.2, 0.3 and 0.4) system. For x=0.1, while cooling, it undergoes a first-order metal-insulator transition at 315 K which is associated with a structural transition from cubic (Pm3m) to tetragonal (I4/mcm) due to Jahn-Teller ordering () which stabilizes a chain like (C-type) antiferromagnetic ground state with . The antiferromagnetic insulator state is insensitive to an applied magnetic field of 7 T. With increase of x, while the nuclear structure at room temperature for x=0.2 and 0.3 remains tetragonal, for x=0.4 it becomes orthorhombic (Imma) where the doping electrons seem to occupy mainly the d x2-y2 symmetry. Further, the JT distortion and the antiferromagnetic interactions decrease with doping and a small negative magnetoresistance appears for . Magnetic measurements show that the dilution of antiferromagnetic interaction results into a spin glass like behaviour at low temperature for the samples with x=0.3 and 0.4. This behaviour is in contrast with the CMR properties of calcium based electron doped systems and hole doped manganites. The stability of C-type antiferromagnetic ordering in the electron doped system with large A-site cationic size may be responsible for the absence of double exchange ferromagnetism and CMR effect.
Journal of Materials Chemistry C, 2019
Highly luminescent hybrid (CH6N3)2MnCl4 featuring unique (Mn3Cl12)6− units in the crystal structu... more Highly luminescent hybrid (CH6N3)2MnCl4 featuring unique (Mn3Cl12)6− units in the crystal structure, exhibits a remarkable 30 K hysteresis across dielectric and magnetic switching.
Materials Research Express, 2014
The effect of rare-earth ion size on the octahedral distortions in rare-earth chromites (RCrO 3 ,... more The effect of rare-earth ion size on the octahedral distortions in rare-earth chromites (RCrO 3 , R = Lu, Tb, Gd, Eu, Sm) crystallizing in the orthorhombic structure has been studied using Raman scattering and synchrotron powder x-ray diffraction up to 20 GPa. From our studies on RCrO 3 we found that the octahedral tilts (distortions) increase with pressure. This is contrary to the earlier report which suggests that in LaCrO 3 , the distortions decrease with pressure leading to a more ordered phase at high pressure. Here we observe that the rate of increase in distortion decreases with the increase in R-ion radii. This occurs due to the reduction in the compression of RO 12 polyhedra with a corresponding increase in the compression of the CrO 6 octahedra with increasing R-ion radii. From the Raman studies, we predict a critical R-ion radii, above which we expect the distortions in RCrO 3 to reduce with increasing pressure leading to what is observed in the case of LaCrO 3. These Raman results are consistent with our pressure dependent structural studies on RCrO 3 (R = Gd, Eu, Sm). Also, our results suggest that the pressure dependence of Néel temperature, T N Cr , (where the Cr 3+ spin orders) in RCrO 3 is mostly affected by the compressions of Cr-O bonds rather than the alteration of octahedral tilts.
EPL (Europhysics Letters), 2013
Raman study on a select few orthochromites, RCrO 3 (R = Y, Lu, Gd, Eu and Sm) shows that the phon... more Raman study on a select few orthochromites, RCrO 3 (R = Y, Lu, Gd, Eu and Sm) shows that the phonon behavior at T N in compounds with magnetic R-ion (Gd and Sm) is remarkably different from that of non-magnetic R-ion (Y, Lu and Eu). While anomalies in most of the observed phonon frequencies in all these compounds may result from the distortion of CrO 6 octahedra due to size effect and magnetostriction arising from Cr-ordering, the anomalous behavior of their linewidths observed at T N for the compounds with only magnetic R-ion suggests spin-phonon coupling. The presence of spin-phonon coupling and the anomalies in the low frequency modes related to R-ion motion in orthochromites (R = Gd and Sm) support the suggestion that the coupling between 4f-3d moments play important role in inducing switchable electric polarization.
Physical Review B, 1995
Our neutron-diffraction study of the single Tl-O layered T18al Sr LaCu05+~system (x =0. 0, 0.4, 0... more Our neutron-diffraction study of the single Tl-O layered T18al Sr LaCu05+~system (x =0. 0, 0.4, 0.7, and 1.0) shows that the in-plane Cu-O(2) bond length decreases monotonically with increase of x. This is consistent with the introduction of holes in Cu02 layers or the appearance of superconductivity in the sample with x =0.4 (T, =22 K) and increase of T, with x, T, =25 and 30 K for samples with x =0.7 and 1.0, respectively. Further, the valence of copper, derived from Cu-0 bond length, increases with increase of x despite the fact that the 0 content decreases as x increases. This clearly suggests that the internal redox mechanism due to the overlap of the empty Tl 6s band with the filled Cu 3d & 2 band xy is responsible for the generation of holes, and therefore superconductivity, in these materials.
![Research paper thumbnail of Superconducting and magnetic properties of TlSr 2 Ca 1 − x R x Cu 2 O 7 [ R =Pr,Tb]](https://attachments.academia-assets.com/103004642/thumbnails/1.jpg)
](Physical Review B, 1995
The magnetic and superconducting properties of the T1Sr2Caq R Cuq07 [R = Pr (+=0. 2-1. 0); Tb (z ... more The magnetic and superconducting properties of the T1Sr2Caq R Cuq07 [R = Pr (+=0. 2-1. 0); Tb (z = 0.6 and 1. 0)] system are reported. The observation of superconductivity in T1Sr2Ca0. 4Pro. sCu20q (T, = 74 K) suggests that the Pr ions are in the trivalent state. The value of the effective magnetic Inoment, p,g-3.15 p,~, for the TISrzCa0. 4Pro. 6CuzOq compound, lies between the free-ion values expected for Pr + (3.58ys) and Pr + (2.54ps). The reduced value of p, s. for the Pr + ion is explained in terms of crystal-field e8'ects. For TlSrz TbCuz07, the Tb magnetic moments order antiferromagnetically at 7.0 K, which is the highest magnetic ordering temperature among the known Tb-containing high-T, related compounds. Superconductivity (T, = 74 and 62 K) and antiferromagnetic ordering (T~= 5 and 6.2 K) coexist in T1Sr2Cao 4Ro sCu20. 7 with R = Pr and Tb, respectively.
Solid State Communications, 1993
Chemistry of Materials, 1997
Insulator-superconductor transition in TlBa 2-x Sr x Ca 0.4 Pr 0.6 Cu 2 O 7-δ has been investigat... more Insulator-superconductor transition in TlBa 2-x Sr x Ca 0.4 Pr 0.6 Cu 2 O 7-δ has been investigated by a joint Rietveld refinement of neutron and X-ray diffraction data, Raman scattering, and infrared absorption studies. For x) 0, the system is an insulator. Substitution of the Ba 2+ ions by smaller Sr 2+ ions leads to a transition from semiconductor to metal then superconductor for x) 1.0. Further, the superconducting transition temperature (T c) increases with x. Results of the joint neutron/X-ray Rietveld refinement revealed that the Tl-O(1) apical bond length does not change appreciably while the Cu-O(1) bond length decreases largely when x increases, consistent with an electron transfer from Cu to Tl. This idea is supported by the Raman scattering measurements showing a large frequency shift of the phonon mode involving the motion of O(1) toward Tl, when Ba is replaced by Sr.
EPL (Europhysics Letters), 2011
APL Materials, 2020
Combining ferroelectricity and magnetism in the same material remains a challenge because it invo... more Combining ferroelectricity and magnetism in the same material remains a challenge because it involves complex crystal chemistry and stringent symmetry requirements. In conventional ferroelectrics, the polarization arises from the second-order Jahn–Teller effect associated with cations of d0 or s2 lone pair electronic configuration. In contrast, the magnetism arises from cations with partially filled d or f electrons. Materials that incorporate these two kinds of cations in different crystallographic sites exhibit multiferroic properties but with weak coupling between magnetism and ferroelectricity. On the other hand, a strong cross-coupling occurs in some materials, where specific spin structures induce weak ferroelectricity below the magnetic ordering temperature. In this article, we discuss a new class of multiferroics where the polar distortion results from chemical ordering. These polar oxides are mainly pyroelectric in the entire temperature range and exhibit magnetoelectric co...
Physical Review B, 1997
Magnetic and magnetoresistance measurements were carried out on a distorted perovskite, Eu 0.58 S... more Magnetic and magnetoresistance measurements were carried out on a distorted perovskite, Eu 0.58 Sr 0.42 MnO 3. In the absence of applied magnetic field, this compound is an insulator down to 5 K. Results of the ac-and dc-susceptibility measurements suggest a spin-glass ground state. An applied field of 7 T drives the insulator ground state to a ferromagnetic metallic state below T C ϭ120 K. For a range of intermediate fields, the compound undergoes insulator-metal-insulator transitions which resemble those of 1:1 Mn 3ϩ /Mn 4ϩ charge-ordered compounds. A temperature-field phase diagram is established which depicts different magnetic and electronic states. ͓S0163-1829͑97͒06109-2͔ PHYSICAL REVIEW B
Journal of Materials Chemistry, 1996
The European Physical Journal B, 2000
ABSTRACT : Neutron and electron diffraction, electrical transport and magnetic measurements have ... more ABSTRACT : Neutron and electron diffraction, electrical transport and magnetic measurements have been carried out on a newly synthesized electron doped Sr1-xCe x MnO3 (x = 0.1, 0.2, 0.3 and 0.4) system. For x=0.1, while cooling, it undergoes a first-order metal-insulator transition at 315 K which is associated with a structural transition from cubic (Pm3m) to tetragonal (I4/mcm) due to Jahn-Teller ordering () which stabilizes a chain like (C-type) antiferromagnetic ground state with . The antiferromagnetic insulator state is insensitive to an applied magnetic field of 7 T. With increase of x, while the nuclear structure at room temperature for x=0.2 and 0.3 remains tetragonal, for x=0.4 it becomes orthorhombic (Imma) where the doping electrons seem to occupy mainly the d x2-y2 symmetry. Further, the JT distortion and the antiferromagnetic interactions decrease with doping and a small negative magnetoresistance appears for . Magnetic measurements show that the dilution of antiferromagnetic interaction results into a spin glass like behaviour at low temperature for the samples with x=0.3 and 0.4. This behaviour is in contrast with the CMR properties of calcium based electron doped systems and hole doped manganites. The stability of C-type antiferromagnetic ordering in the electron doped system with large A-site cationic size may be responsible for the absence of double exchange ferromagnetism and CMR effect.
Journal of Materials Chemistry C, 2019
Highly luminescent hybrid (CH6N3)2MnCl4 featuring unique (Mn3Cl12)6− units in the crystal structu... more Highly luminescent hybrid (CH6N3)2MnCl4 featuring unique (Mn3Cl12)6− units in the crystal structure, exhibits a remarkable 30 K hysteresis across dielectric and magnetic switching.
Materials Research Express, 2014
The effect of rare-earth ion size on the octahedral distortions in rare-earth chromites (RCrO 3 ,... more The effect of rare-earth ion size on the octahedral distortions in rare-earth chromites (RCrO 3 , R = Lu, Tb, Gd, Eu, Sm) crystallizing in the orthorhombic structure has been studied using Raman scattering and synchrotron powder x-ray diffraction up to 20 GPa. From our studies on RCrO 3 we found that the octahedral tilts (distortions) increase with pressure. This is contrary to the earlier report which suggests that in LaCrO 3 , the distortions decrease with pressure leading to a more ordered phase at high pressure. Here we observe that the rate of increase in distortion decreases with the increase in R-ion radii. This occurs due to the reduction in the compression of RO 12 polyhedra with a corresponding increase in the compression of the CrO 6 octahedra with increasing R-ion radii. From the Raman studies, we predict a critical R-ion radii, above which we expect the distortions in RCrO 3 to reduce with increasing pressure leading to what is observed in the case of LaCrO 3. These Raman results are consistent with our pressure dependent structural studies on RCrO 3 (R = Gd, Eu, Sm). Also, our results suggest that the pressure dependence of Néel temperature, T N Cr , (where the Cr 3+ spin orders) in RCrO 3 is mostly affected by the compressions of Cr-O bonds rather than the alteration of octahedral tilts.
EPL (Europhysics Letters), 2013
Raman study on a select few orthochromites, RCrO 3 (R = Y, Lu, Gd, Eu and Sm) shows that the phon... more Raman study on a select few orthochromites, RCrO 3 (R = Y, Lu, Gd, Eu and Sm) shows that the phonon behavior at T N in compounds with magnetic R-ion (Gd and Sm) is remarkably different from that of non-magnetic R-ion (Y, Lu and Eu). While anomalies in most of the observed phonon frequencies in all these compounds may result from the distortion of CrO 6 octahedra due to size effect and magnetostriction arising from Cr-ordering, the anomalous behavior of their linewidths observed at T N for the compounds with only magnetic R-ion suggests spin-phonon coupling. The presence of spin-phonon coupling and the anomalies in the low frequency modes related to R-ion motion in orthochromites (R = Gd and Sm) support the suggestion that the coupling between 4f-3d moments play important role in inducing switchable electric polarization.
Physical Review B, 1995
Our neutron-diffraction study of the single Tl-O layered T18al Sr LaCu05+~system (x =0. 0, 0.4, 0... more Our neutron-diffraction study of the single Tl-O layered T18al Sr LaCu05+~system (x =0. 0, 0.4, 0.7, and 1.0) shows that the in-plane Cu-O(2) bond length decreases monotonically with increase of x. This is consistent with the introduction of holes in Cu02 layers or the appearance of superconductivity in the sample with x =0.4 (T, =22 K) and increase of T, with x, T, =25 and 30 K for samples with x =0.7 and 1.0, respectively. Further, the valence of copper, derived from Cu-0 bond length, increases with increase of x despite the fact that the 0 content decreases as x increases. This clearly suggests that the internal redox mechanism due to the overlap of the empty Tl 6s band with the filled Cu 3d & 2 band xy is responsible for the generation of holes, and therefore superconductivity, in these materials.
Physical Review B, 1995
The magnetic and superconducting properties of the T1Sr2Caq R Cuq07 [R = Pr (+=0. 2-1. 0); Tb (z ... more The magnetic and superconducting properties of the T1Sr2Caq R Cuq07 [R = Pr (+=0. 2-1. 0); Tb (z = 0.6 and 1. 0)] system are reported. The observation of superconductivity in T1Sr2Ca0. 4Pro. sCu20q (T, = 74 K) suggests that the Pr ions are in the trivalent state. The value of the effective magnetic Inoment, p,g-3.15 p,~, for the TISrzCa0. 4Pro. 6CuzOq compound, lies between the free-ion values expected for Pr + (3.58ys) and Pr + (2.54ps). The reduced value of p, s. for the Pr + ion is explained in terms of crystal-field e8'ects. For TlSrz TbCuz07, the Tb magnetic moments order antiferromagnetically at 7.0 K, which is the highest magnetic ordering temperature among the known Tb-containing high-T, related compounds. Superconductivity (T, = 74 and 62 K) and antiferromagnetic ordering (T~= 5 and 6.2 K) coexist in T1Sr2Cao 4Ro sCu20. 7 with R = Pr and Tb, respectively.
Solid State Communications, 1993
Chemistry of Materials, 1997
Insulator-superconductor transition in TlBa 2-x Sr x Ca 0.4 Pr 0.6 Cu 2 O 7-δ has been investigat... more Insulator-superconductor transition in TlBa 2-x Sr x Ca 0.4 Pr 0.6 Cu 2 O 7-δ has been investigated by a joint Rietveld refinement of neutron and X-ray diffraction data, Raman scattering, and infrared absorption studies. For x) 0, the system is an insulator. Substitution of the Ba 2+ ions by smaller Sr 2+ ions leads to a transition from semiconductor to metal then superconductor for x) 1.0. Further, the superconducting transition temperature (T c) increases with x. Results of the joint neutron/X-ray Rietveld refinement revealed that the Tl-O(1) apical bond length does not change appreciably while the Cu-O(1) bond length decreases largely when x increases, consistent with an electron transfer from Cu to Tl. This idea is supported by the Raman scattering measurements showing a large frequency shift of the phonon mode involving the motion of O(1) toward Tl, when Ba is replaced by Sr.