P. K. Manna | University of Manitoba (original) (raw)
Ph.D. (Physics) from Bhabha Atomic Research Centre/University of Mumbai, India
Thesis-title: Exchange Bias in Oxide-based Magnetic Nanoparticles.
SKILLS acquired during the Ph.D.:
•Synthesis of bi-magnetic core-shell type nanoparticles using wet-chemical methods.
Experimental techniques used:
•X-ray diffraction.
•Neutron diffraction at DHRUVA reactor, BARC, Mumbai, India.
•Polarized neutron small angle scattering (SANSPOL).
•Transmission electron microscopy (TEM).
•DC/AC-magnetization using VSM and SQUID.
Computational techniques used:
•Rietveld refinement using the FULLPROF program:
-Detailed crystal structure analysis, from the refinement of the x-ray and neutron powder diffraction data, such as positions of the atoms in a unit cell, bond length and bond angle between the different atoms in a unit cell, crystal structure.
-Determination of the magnetic structure from the refinement of variable temperature neutron diffraction patterns.
•Analysis of SANSPOL-data using the BerSANS and sasfit softwares.
•Analysis of TEM images using the ImageJ software.
•Data analysis using the MATHEMATICA and ORIGIN programs.
International Exposures:
•Experienced in low temperature and high magnetic field neutron diffraction experiment at the DMC powder diffractometer, Paul Scherrer Institute (PSI), Switzerland.
•Experienced in low temperature and high magnetic field SANSPOL experiment at the SANS-I instrument, PSI, Switzerland.
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Related Authors
Homi Bhabha National Institute (HBNI, BARC, MUMBAI)
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Papers by P. K. Manna
We propose a new and highly effective tool to add to the ever shrinking toolbox for combating inf... more We propose a new and highly effective tool to add to the ever shrinking toolbox for combating infections caused by antibiotic resistant bacteria; N-chloramine and quaternized N-chloramine were coated onto iron-oxide magnetic nanoparticles to generate antibacterial MNPs. Two differently-sized primary iron-oxide nanoparticles (3 nm and 10 nm) were synthesized and coated with silica and (3-chloropropyl)triethoxysilane, allowing subsequent introduction of N-chloramine precursors – dimethyl hydantoin (DMH) and quaternized dimethyl hydantoin (QDMH). The functionalized MNPs (MNP@DMH and MNP@QDMH) have a clear core–shell structure as evidenced by TEM images. Fe3O4 was identified (by combining X-ray diffraction with Mössbauer spectroscopy) to be the iron oxide in the 10 nm MNPs, while γ-Fe2O3 and Fe3O4 were the 3 nm MNP's oxide phases. Both MNPs (3 nm and 10 nm) have good magnetic responses, with saturation magnetizations of 40 ± 4 emu g−1 and 65 ± 2 emu g−1, respectively. Chlorination activated the antibacterial function and yielded two antibacterial MNPs: MNP@DMCl and MNP@QASCl. At the equivalent [Cl+] of 50 ppm, both coatings demonstrated fast inactivation of the model bacteria methicilin-resistant Staphylococcus aureus (MRSA) and multi-drug resistant (MDR) Pseudomonas aeruginosa. For either size of primary MNPs, MNP@QDMCl is more effective than MNP@DMCl. A hand-held magnet could quickly remove >99% of the functionalized MNPs from a wound simulant within 2 minutes.
Journal of Materials Chemistry
Improvements in magnetodielectric and multiferroic properties are essential for visualizing the r... more Improvements in magnetodielectric and multiferroic properties are essential for visualizing the real application of multiferroics, precisely, BiFeO 3 (BFO). An enhancement of multiferroic and magnetodielectric properties has been achieved for chemically prepared nanocrystalline BFO by virtue of Sm doping. The X-ray diffraction study confirms the growth of single phase nanocrystalline BFO which corroborates TEM observation. The magnetic study delineates the ferromagnetic behavior of nanocrystalline Sm-doped BFO samples even at room temperature, which is absent in pristine samples.
Journal of Physics: Conference Series, 2014
ABSTRACT We report the presence of an exchange bias effect in a layered iridate compound, Sr2IrO4... more ABSTRACT We report the presence of an exchange bias effect in a layered iridate compound, Sr2IrO4, in polycrystalline form. The Rietveld refinement of the x-ray diffraction pattern shows that Sr2IrO4 crystallizes in a tetragonal structure (I41 acd). The temperature dependence of zero-field cooled (ZFC) and field cooled (FC) magnetization measurements show a magnetic ordering temperature of ~240 K, which is considered as its canted antiferromagnetic ordering temperature. An irreversibility between ZFC and FC curves is observed at T irr, which decreases with an increasing field (H). The T irr vs. H 2/3 plot follows the Almeida-Thouless (AT) line. The presence of an AT line and a significant amount of coercivity (~0.3 T) at 5 K hint a cluster-glass like behaviour in Sr2IrO4 polycrystals. A negative exchange bias effect has been observed at 5 K with an exchange bias field of 0.018 T, which is attributed to an interfacial exchange interaction between a canted antiferromagnetic phase and a probable cluster-glass phase. This is the first report on the observation of an exchange bias effect in Sr2IrO4. Further studies are underway for a detailed understanding.
RSC Advances, 2013
ABSTRACT Tuning of the tin oxide (SnO/SnO2) heterojunction (TOHJ) has been made possible by heati... more ABSTRACT Tuning of the tin oxide (SnO/SnO2) heterojunction (TOHJ) has been made possible by heating the as-prepared p-type SnO semiconductor in air in a controlled fashion. Thus a better photocatalytic activity for dye degradation under UV, visible as well as solar light irradiation was achieved. Multiple reflection of light and the TOHJ of SnO plates facilitate the photocatalysis reactions.
We have performed variable temperature neutron powder diffraction experiment on single phase La0.... more We have performed variable temperature neutron powder diffraction experiment on single phase La0.2Ce0.8CrO3 compound. The Rietveld analysis of the powder diffraction patterns confirms the presence of G-type antiferromagnetic alignment of Cr3+ ionic moments up to 250K in an orthorhombic perovskite (Space group: Pbnm) structure with magnetic moment oriented along the crystallographic b-axis. At the lowest available temperature i.e. 22 K, the magnetic moment of the Cr3+ ion is found to be 2.56 (4) μB which is close to the spin only magnetic moment of free Cr3+ ion (3 μB).The thermal evolution of the Cr3+ magnetic moment has been well fitted using a Brillouin function.
Crystal Growth & Design, 2014
ABSTRACT Ultralong Ag1.92Mo3O10 center dot H2O nanowires have been serendipitously obtained due t... more ABSTRACT Ultralong Ag1.92Mo3O10 center dot H2O nanowires have been serendipitously obtained due to selective etching of ammonium phosphomolybdate (APM) only by Ag+ ions in water under stirring conditions. The spherical yellow APM particle upon etching by Ag+ ions generates a hollow sphere, and PO43- ions are expelled as a consequence of etching. The etching and hollowing disrupt the APM structure. Concentration of the etching agent and reaction time are crucial for the formation of Ag1.92Mo3O10 center dot H2O nanowire. The growth of nanowires occurs probably due to etching followed by Ostwald ripening, oriented attachment, and splitting process. Finally, the as-synthesized nanowire exhibits a high capacity to adsorb cationic dyes on its surface. It shows superb adsorption properties, with maximum adsorption capacity of 110 mg g(1), 175 mg g(1), 160 mg g(1) for Methylene Blue, Methyl Green, Crystal Violet, respectively. Moreover, the adsorption process of Methylene Blue on the nanomaterial was investigated taking it as a representative adsorbate. The selective adsorption capability of the nanomaterial toward cationic dye molecules makes it a competent candidate for water purification.
ABSTRACT We report the exact nature of magnetic ordering in La1-xCexCrO3 (x = 0.2, 0.8, 1.0) nano... more ABSTRACT We report the exact nature of magnetic ordering in La1-xCexCrO3 (x = 0.2, 0.8, 1.0) nanoparticles (diameter: ~43 nm) using microscopic and macroscopic measurement techniques. The variable temperature neutron diffraction experiments revealed a G-type antiferromagnetic ordering of Cr3+ ions in an orthorhombic perovskite structure with magnetic moment oriented along the crystallographic b-axis. A decrease in Néel temperature has been observed with increasing x, which has been assigned to a decrease in the Cr-O-Cr bond angle obtained from the Rietveld refinement analysis of the neutron diffraction patterns. The observed decrease in lattice parameters with increasing x has been explained in terms lesser ionic radius of Ce3+ (1.34 A˚) ion compared to that of La3+ (1.36 A˚).
Journal of Alloys and Compounds, 2014
Large leakage current and a very low magnetic moment are the two most disadvantages of BiFeO 3 (B... more Large leakage current and a very low magnetic moment are the two most disadvantages of BiFeO 3 (BFO), which hinder the possibilities of its application in modern devices. An enhancement of the multiferroic properties of BFO is a real challenge to the scientific community. We are able to achieve improve magnetic, electric and magneto-dielectric (MD) properties of sol-gel prepared nanocrystalline BFO by virtue of the beneficial effect of gadolinium doping. The phase-purity and nanocrystalline nature of the samples have been confirmed by the X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. Both dc and ac electrical properties were measured to understand the detail charge transport mechanism. The dc electrical resistivity was found to arise due to a variable range hopping conduction mechanism. The variation of ac-conductivity, as a function of frequency in the range (20 Hz-1 MHz) and temperature (298-523 K), was explained on the basis of the correlated barrier hoping (CBH) conduction mechanism. The origin of the improved magnetic and electrical properties have been attributed to a possible suppression of the inhomogeneous magnetic spin structure and/or broken periodicity of the spin cycloid of BFO due to smaller crystallite size, and a decrease of the oxygen vacancies. Our findings demonstrate the fundamental importance of doping in enhancing the multiferroic properties, which would open up the possibility of using BFO in designing spintronic devices.
Applied Physics Letters, 2007
Magnetization studies on La0.5Gd0.2Sr0.3MnO3 (LGSMO) nanoparticles (~20 nm) reveal superparamagne... more Magnetization studies on La0.5Gd0.2Sr0.3MnO3 (LGSMO) nanoparticles (~20 nm) reveal superparamagnetic phase associated with this system and thereby contrasting from cluster glass (CG) phase of its bulk counterpart. Doping of Gd on La sites and its antiferromagnetic coupling with Mn lattices are expected to induce random magnetic disorder in the magnetic lattice of LGSMO system. Study reveals that random magnetic disorder, which results in CG phase in an otherwise long range ordered ferromagnetic host matrix of bulk, does not have similar significant effect when the uniformity of the host matrix reduces to nanosize. On the contrary, analysis brings out that magnetic properties of LGSMO nanoparticles are primarily decided by its nanodimension having physical size of ~20 nm, which yield single domain magnetic entities of dimension of ~12 nm surrounded by a magnetic dead layer of ~4 nm.
Physics Reports, Oct 26, 2013
Exchange bias and magnetic proximity effects are two novel phenomena that are in the limelight be... more Exchange bias and magnetic proximity effects are two novel phenomena that are in the limelight because of their fundamental and technological importance. Since both phenomena are interfacial in origin, we review these together. In the first part of this review, we have discussed the basics of these two phenomena. Subsequently, we have described numerous experimental examples involving a variety of composite magnetic materials and heterostructures. The recent theoretical models of these two interface phenomena have also been described. Finally, we have shed light on an obvious question: can one expect both these phenomena to occur together in any magnetically coupled system? We conclude that one can enhance the operating temperature of an exchanged biased device by exploiting the magnetic proximity effect.
We report an extraordinary coexistence of sign reversal of both magnetization and exchange bias f... more We report an extraordinary coexistence of sign reversal of both magnetization and exchange bias field in the La0.2Ce0.8CrO3 nanoparticles. From the high resolution transmission electron microscopy image, and field dependence of thermoremanent and isothermoremanent magnetization measurements, the nanoparticles are found to be of core-shell nature. The core-shell configuration with an antiferromagnetic core of the Cr3+ and Ce3+ spins and a disordered shell with the uncompensated spins, explains the sign reversal of both magnetization and exchange bias field. The present study shows an excellent way of tuning the sign of both magnetization and exchange bias field in a single magnetic system.
RSC Adv., 2013, Accepted Manuscript, Oct 11, 2013
Tunning of tin oxide (SnO/SnO2) heterojunction (TOHJ) has been possible by control heating the as... more Tunning of tin oxide (SnO/SnO2) heterojunction (TOHJ) has been possible by control heating the as-prepared p-type semiconductor SnO in air. Thus better photocatalyic activity for dye degradation under UV, visible as well as solar light irradiation is achieved. Multiple reflection of light and TOHJ of SnO plates facilate the photocatalysis reaction.
Langmuir 29 (2013) 9179
A facile, cost-effective, surfactant-free chemical route has been demonstrated for the fabricatio... more A facile, cost-effective, surfactant-free chemical route has been demonstrated for the fabrication of porous β-Co(OH)2 hierarchical nanostructure in gram level simply by adopting cobalt acetate as a precursor salt and ethanolamine as a hydrolyzing agent at room temperature. A couple of different morphologies of β-Co(OH)2 have been distinctly identified by varying the mole ratio of the precursor and hydrolyzing agent. The cyclic voltammetry measurements on β-Co(OH)2 displayed significantly high capacitance. The specific capacitance obtained from charge–discharge measurements made at a discharge current of 1 A/g is 416 F/g for the Co(OH)2 sample obtained at room temperature. The charge–discharge stability measurements indicate retention of specific capacitance about 93% after 500 continuous charge–discharge cycles at a current density of 1 A g–1. The capacitive behavior of the other synthesized morphology was also accounted. The nanoflower-shaped porous β-Co(OH)2 with a characteristic three-dimensional architecture accompanied highest pore volume which made it promising electrode material for supercapacitor application. The porous nanostructures accompanied by high surface area facilitates the contact and transport of electrolyte, providing longer electron pathways and therefore giving rise to highest capacitance in nanoflower morphology. From a broad view, this study reveals a low-temperature synthetic route of β-Co(OH)2 of various morphologies, qualifying it as supercapacitor electrode material.
J. Appl. Phys. 113 (2013) 173906
"We have carried out magnetization measurements on BiFeO3 core/NiFe2O4 shell nanoparticles, and s... more "We have carried out magnetization measurements on BiFeO3 core/NiFe2O4 shell nanoparticles, and searched for the exchange bias phenomenon in this system. The core-shell nature of these nanoparticles has been established from the transmission electron microscopy images. The neutron diffraction study establishes that the core is G-type antiferromagnetic, while the shell is ferrimagnetic in nature. The search for an exchange bias phenomenon in the core-shell system shows a shift of the field-cooled (FC) hysteresis loops, at 5K, along the magnetic field axis. The present investigation shows an unusual shift of the zero field-cooled (ZFC) hysteresis loop along the magnetic field axis as well. An enhancement of the remanent magnetization along with a decrease in the coercivity is also observed in the FC case, as compared to the corresponding values in the ZFC case, which is not found commonly in any conventional exchange-biased system. All these features indicate the presence of an interface exchange coupling between core and shell of the studied nanoparticles."
We report the evidence of a core-shell structure in the antiferromagnetic La0.2Ce0.8CrO3 nanopart... more We report the evidence of a core-shell structure in the antiferromagnetic La0.2Ce0.8CrO3 nanoparticles by using a combination of neutron diffraction, polarized neutron small angle scattering (SANSPOL), and dcmagnetization techniques. The neutron diffraction study establishes that the present nanoparticles are antiferromagnetic in nature. The magnetic scattering in the SANSPOL study arises from the shell part of the nanoparticles due to the disordered surface spins. The analysis of the SANSPOL data shows that these nanoparticles have a mean core diameter of 12.3 nm, and a shell thickness of 2.8 nm, giving a core-shell structure with an antiferromagnetic core, and a shell with a net magnetic moment under an applied magnetic field.
We report the magnetic proximity effect in a ferrimagnetic Fe3O4 core/ferrimagnetic gamma-Mn2O3 s... more We report the magnetic proximity effect in a ferrimagnetic Fe3O4 core/ferrimagnetic gamma-Mn2O3 shell nanoparticle-system, in terms of an enhancement of the Curie temperature (Tc) of gamma-Mn2O3 shell (~66 K) compared to its bulk value (~40 K), and the presence of magnetic ordering in its so-called paramagnetic region (i.e. above 66 K),. The ferrimagnetic nature of both core and shell has been found from the neutron diffraction study. The origin of these two features of magnetic proximity effect has been ascribed to the proximity of gamma-Mn2O3 shell with a high-Tc Fe3O4 core (~858 K in bulk form), and an interface exchange coupling between core and shell. Interestingly, we did not observe any exchange bias effect, which has been interpreted as a signature of a weak interface exchange coupling between core and shell. The present study brings out the importance of the relative strength of the interface coupling in governing the simultaneous occurrence of magnetic proximity effect, and exchange bias phenomenon in a single system.
We have observed conventional signatures of exchange bias (EB), in the form of a shift in the fie... more We have observed conventional signatures of exchange bias (EB), in the form of a shift in the field-cooled hysteresis loop, and a training effect, in BiFe0.8Mn0.2O3 nanoparticles. From neutron diffraction, thermoremanent magnetization, and isothermoremanent magnetization measurements, the nanoparticles are found to be core shell in nature, consisting of an antiferromagnetic (AFM) core, and a two-dimensional diluted AFM (DAFF) shell with a net magnetization under a field. The analysis of the training effect data using Binek's model shows that the observed loop shift arises entirely due to an interface exchange coupling between the core and shell, and the intrinsic contribution of the DAFF shell to the total loop shift is zero. A significantly high value of the EB field has been observed at room temperature. The present study is useful to understand the origin of EB in other DAFF-based systems as well.
We propose a new and highly effective tool to add to the ever shrinking toolbox for combating inf... more We propose a new and highly effective tool to add to the ever shrinking toolbox for combating infections caused by antibiotic resistant bacteria; N-chloramine and quaternized N-chloramine were coated onto iron-oxide magnetic nanoparticles to generate antibacterial MNPs. Two differently-sized primary iron-oxide nanoparticles (3 nm and 10 nm) were synthesized and coated with silica and (3-chloropropyl)triethoxysilane, allowing subsequent introduction of N-chloramine precursors – dimethyl hydantoin (DMH) and quaternized dimethyl hydantoin (QDMH). The functionalized MNPs (MNP@DMH and MNP@QDMH) have a clear core–shell structure as evidenced by TEM images. Fe3O4 was identified (by combining X-ray diffraction with Mössbauer spectroscopy) to be the iron oxide in the 10 nm MNPs, while γ-Fe2O3 and Fe3O4 were the 3 nm MNP's oxide phases. Both MNPs (3 nm and 10 nm) have good magnetic responses, with saturation magnetizations of 40 ± 4 emu g−1 and 65 ± 2 emu g−1, respectively. Chlorination activated the antibacterial function and yielded two antibacterial MNPs: MNP@DMCl and MNP@QASCl. At the equivalent [Cl+] of 50 ppm, both coatings demonstrated fast inactivation of the model bacteria methicilin-resistant Staphylococcus aureus (MRSA) and multi-drug resistant (MDR) Pseudomonas aeruginosa. For either size of primary MNPs, MNP@QDMCl is more effective than MNP@DMCl. A hand-held magnet could quickly remove >99% of the functionalized MNPs from a wound simulant within 2 minutes.
Journal of Materials Chemistry
Improvements in magnetodielectric and multiferroic properties are essential for visualizing the r... more Improvements in magnetodielectric and multiferroic properties are essential for visualizing the real application of multiferroics, precisely, BiFeO 3 (BFO). An enhancement of multiferroic and magnetodielectric properties has been achieved for chemically prepared nanocrystalline BFO by virtue of Sm doping. The X-ray diffraction study confirms the growth of single phase nanocrystalline BFO which corroborates TEM observation. The magnetic study delineates the ferromagnetic behavior of nanocrystalline Sm-doped BFO samples even at room temperature, which is absent in pristine samples.
Journal of Physics: Conference Series, 2014
ABSTRACT We report the presence of an exchange bias effect in a layered iridate compound, Sr2IrO4... more ABSTRACT We report the presence of an exchange bias effect in a layered iridate compound, Sr2IrO4, in polycrystalline form. The Rietveld refinement of the x-ray diffraction pattern shows that Sr2IrO4 crystallizes in a tetragonal structure (I41 acd). The temperature dependence of zero-field cooled (ZFC) and field cooled (FC) magnetization measurements show a magnetic ordering temperature of ~240 K, which is considered as its canted antiferromagnetic ordering temperature. An irreversibility between ZFC and FC curves is observed at T irr, which decreases with an increasing field (H). The T irr vs. H 2/3 plot follows the Almeida-Thouless (AT) line. The presence of an AT line and a significant amount of coercivity (~0.3 T) at 5 K hint a cluster-glass like behaviour in Sr2IrO4 polycrystals. A negative exchange bias effect has been observed at 5 K with an exchange bias field of 0.018 T, which is attributed to an interfacial exchange interaction between a canted antiferromagnetic phase and a probable cluster-glass phase. This is the first report on the observation of an exchange bias effect in Sr2IrO4. Further studies are underway for a detailed understanding.
RSC Advances, 2013
ABSTRACT Tuning of the tin oxide (SnO/SnO2) heterojunction (TOHJ) has been made possible by heati... more ABSTRACT Tuning of the tin oxide (SnO/SnO2) heterojunction (TOHJ) has been made possible by heating the as-prepared p-type SnO semiconductor in air in a controlled fashion. Thus a better photocatalytic activity for dye degradation under UV, visible as well as solar light irradiation was achieved. Multiple reflection of light and the TOHJ of SnO plates facilitate the photocatalysis reactions.
We have performed variable temperature neutron powder diffraction experiment on single phase La0.... more We have performed variable temperature neutron powder diffraction experiment on single phase La0.2Ce0.8CrO3 compound. The Rietveld analysis of the powder diffraction patterns confirms the presence of G-type antiferromagnetic alignment of Cr3+ ionic moments up to 250K in an orthorhombic perovskite (Space group: Pbnm) structure with magnetic moment oriented along the crystallographic b-axis. At the lowest available temperature i.e. 22 K, the magnetic moment of the Cr3+ ion is found to be 2.56 (4) μB which is close to the spin only magnetic moment of free Cr3+ ion (3 μB).The thermal evolution of the Cr3+ magnetic moment has been well fitted using a Brillouin function.
Crystal Growth & Design, 2014
ABSTRACT Ultralong Ag1.92Mo3O10 center dot H2O nanowires have been serendipitously obtained due t... more ABSTRACT Ultralong Ag1.92Mo3O10 center dot H2O nanowires have been serendipitously obtained due to selective etching of ammonium phosphomolybdate (APM) only by Ag+ ions in water under stirring conditions. The spherical yellow APM particle upon etching by Ag+ ions generates a hollow sphere, and PO43- ions are expelled as a consequence of etching. The etching and hollowing disrupt the APM structure. Concentration of the etching agent and reaction time are crucial for the formation of Ag1.92Mo3O10 center dot H2O nanowire. The growth of nanowires occurs probably due to etching followed by Ostwald ripening, oriented attachment, and splitting process. Finally, the as-synthesized nanowire exhibits a high capacity to adsorb cationic dyes on its surface. It shows superb adsorption properties, with maximum adsorption capacity of 110 mg g(1), 175 mg g(1), 160 mg g(1) for Methylene Blue, Methyl Green, Crystal Violet, respectively. Moreover, the adsorption process of Methylene Blue on the nanomaterial was investigated taking it as a representative adsorbate. The selective adsorption capability of the nanomaterial toward cationic dye molecules makes it a competent candidate for water purification.
ABSTRACT We report the exact nature of magnetic ordering in La1-xCexCrO3 (x = 0.2, 0.8, 1.0) nano... more ABSTRACT We report the exact nature of magnetic ordering in La1-xCexCrO3 (x = 0.2, 0.8, 1.0) nanoparticles (diameter: ~43 nm) using microscopic and macroscopic measurement techniques. The variable temperature neutron diffraction experiments revealed a G-type antiferromagnetic ordering of Cr3+ ions in an orthorhombic perovskite structure with magnetic moment oriented along the crystallographic b-axis. A decrease in Néel temperature has been observed with increasing x, which has been assigned to a decrease in the Cr-O-Cr bond angle obtained from the Rietveld refinement analysis of the neutron diffraction patterns. The observed decrease in lattice parameters with increasing x has been explained in terms lesser ionic radius of Ce3+ (1.34 A˚) ion compared to that of La3+ (1.36 A˚).
Journal of Alloys and Compounds, 2014
Large leakage current and a very low magnetic moment are the two most disadvantages of BiFeO 3 (B... more Large leakage current and a very low magnetic moment are the two most disadvantages of BiFeO 3 (BFO), which hinder the possibilities of its application in modern devices. An enhancement of the multiferroic properties of BFO is a real challenge to the scientific community. We are able to achieve improve magnetic, electric and magneto-dielectric (MD) properties of sol-gel prepared nanocrystalline BFO by virtue of the beneficial effect of gadolinium doping. The phase-purity and nanocrystalline nature of the samples have been confirmed by the X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. Both dc and ac electrical properties were measured to understand the detail charge transport mechanism. The dc electrical resistivity was found to arise due to a variable range hopping conduction mechanism. The variation of ac-conductivity, as a function of frequency in the range (20 Hz-1 MHz) and temperature (298-523 K), was explained on the basis of the correlated barrier hoping (CBH) conduction mechanism. The origin of the improved magnetic and electrical properties have been attributed to a possible suppression of the inhomogeneous magnetic spin structure and/or broken periodicity of the spin cycloid of BFO due to smaller crystallite size, and a decrease of the oxygen vacancies. Our findings demonstrate the fundamental importance of doping in enhancing the multiferroic properties, which would open up the possibility of using BFO in designing spintronic devices.
Applied Physics Letters, 2007
Magnetization studies on La0.5Gd0.2Sr0.3MnO3 (LGSMO) nanoparticles (~20 nm) reveal superparamagne... more Magnetization studies on La0.5Gd0.2Sr0.3MnO3 (LGSMO) nanoparticles (~20 nm) reveal superparamagnetic phase associated with this system and thereby contrasting from cluster glass (CG) phase of its bulk counterpart. Doping of Gd on La sites and its antiferromagnetic coupling with Mn lattices are expected to induce random magnetic disorder in the magnetic lattice of LGSMO system. Study reveals that random magnetic disorder, which results in CG phase in an otherwise long range ordered ferromagnetic host matrix of bulk, does not have similar significant effect when the uniformity of the host matrix reduces to nanosize. On the contrary, analysis brings out that magnetic properties of LGSMO nanoparticles are primarily decided by its nanodimension having physical size of ~20 nm, which yield single domain magnetic entities of dimension of ~12 nm surrounded by a magnetic dead layer of ~4 nm.
Physics Reports, Oct 26, 2013
Exchange bias and magnetic proximity effects are two novel phenomena that are in the limelight be... more Exchange bias and magnetic proximity effects are two novel phenomena that are in the limelight because of their fundamental and technological importance. Since both phenomena are interfacial in origin, we review these together. In the first part of this review, we have discussed the basics of these two phenomena. Subsequently, we have described numerous experimental examples involving a variety of composite magnetic materials and heterostructures. The recent theoretical models of these two interface phenomena have also been described. Finally, we have shed light on an obvious question: can one expect both these phenomena to occur together in any magnetically coupled system? We conclude that one can enhance the operating temperature of an exchanged biased device by exploiting the magnetic proximity effect.
We report an extraordinary coexistence of sign reversal of both magnetization and exchange bias f... more We report an extraordinary coexistence of sign reversal of both magnetization and exchange bias field in the La0.2Ce0.8CrO3 nanoparticles. From the high resolution transmission electron microscopy image, and field dependence of thermoremanent and isothermoremanent magnetization measurements, the nanoparticles are found to be of core-shell nature. The core-shell configuration with an antiferromagnetic core of the Cr3+ and Ce3+ spins and a disordered shell with the uncompensated spins, explains the sign reversal of both magnetization and exchange bias field. The present study shows an excellent way of tuning the sign of both magnetization and exchange bias field in a single magnetic system.
RSC Adv., 2013, Accepted Manuscript, Oct 11, 2013
Tunning of tin oxide (SnO/SnO2) heterojunction (TOHJ) has been possible by control heating the as... more Tunning of tin oxide (SnO/SnO2) heterojunction (TOHJ) has been possible by control heating the as-prepared p-type semiconductor SnO in air. Thus better photocatalyic activity for dye degradation under UV, visible as well as solar light irradiation is achieved. Multiple reflection of light and TOHJ of SnO plates facilate the photocatalysis reaction.
Langmuir 29 (2013) 9179
A facile, cost-effective, surfactant-free chemical route has been demonstrated for the fabricatio... more A facile, cost-effective, surfactant-free chemical route has been demonstrated for the fabrication of porous β-Co(OH)2 hierarchical nanostructure in gram level simply by adopting cobalt acetate as a precursor salt and ethanolamine as a hydrolyzing agent at room temperature. A couple of different morphologies of β-Co(OH)2 have been distinctly identified by varying the mole ratio of the precursor and hydrolyzing agent. The cyclic voltammetry measurements on β-Co(OH)2 displayed significantly high capacitance. The specific capacitance obtained from charge–discharge measurements made at a discharge current of 1 A/g is 416 F/g for the Co(OH)2 sample obtained at room temperature. The charge–discharge stability measurements indicate retention of specific capacitance about 93% after 500 continuous charge–discharge cycles at a current density of 1 A g–1. The capacitive behavior of the other synthesized morphology was also accounted. The nanoflower-shaped porous β-Co(OH)2 with a characteristic three-dimensional architecture accompanied highest pore volume which made it promising electrode material for supercapacitor application. The porous nanostructures accompanied by high surface area facilitates the contact and transport of electrolyte, providing longer electron pathways and therefore giving rise to highest capacitance in nanoflower morphology. From a broad view, this study reveals a low-temperature synthetic route of β-Co(OH)2 of various morphologies, qualifying it as supercapacitor electrode material.
J. Appl. Phys. 113 (2013) 173906
"We have carried out magnetization measurements on BiFeO3 core/NiFe2O4 shell nanoparticles, and s... more "We have carried out magnetization measurements on BiFeO3 core/NiFe2O4 shell nanoparticles, and searched for the exchange bias phenomenon in this system. The core-shell nature of these nanoparticles has been established from the transmission electron microscopy images. The neutron diffraction study establishes that the core is G-type antiferromagnetic, while the shell is ferrimagnetic in nature. The search for an exchange bias phenomenon in the core-shell system shows a shift of the field-cooled (FC) hysteresis loops, at 5K, along the magnetic field axis. The present investigation shows an unusual shift of the zero field-cooled (ZFC) hysteresis loop along the magnetic field axis as well. An enhancement of the remanent magnetization along with a decrease in the coercivity is also observed in the FC case, as compared to the corresponding values in the ZFC case, which is not found commonly in any conventional exchange-biased system. All these features indicate the presence of an interface exchange coupling between core and shell of the studied nanoparticles."
We report the evidence of a core-shell structure in the antiferromagnetic La0.2Ce0.8CrO3 nanopart... more We report the evidence of a core-shell structure in the antiferromagnetic La0.2Ce0.8CrO3 nanoparticles by using a combination of neutron diffraction, polarized neutron small angle scattering (SANSPOL), and dcmagnetization techniques. The neutron diffraction study establishes that the present nanoparticles are antiferromagnetic in nature. The magnetic scattering in the SANSPOL study arises from the shell part of the nanoparticles due to the disordered surface spins. The analysis of the SANSPOL data shows that these nanoparticles have a mean core diameter of 12.3 nm, and a shell thickness of 2.8 nm, giving a core-shell structure with an antiferromagnetic core, and a shell with a net magnetic moment under an applied magnetic field.
We report the magnetic proximity effect in a ferrimagnetic Fe3O4 core/ferrimagnetic gamma-Mn2O3 s... more We report the magnetic proximity effect in a ferrimagnetic Fe3O4 core/ferrimagnetic gamma-Mn2O3 shell nanoparticle-system, in terms of an enhancement of the Curie temperature (Tc) of gamma-Mn2O3 shell (~66 K) compared to its bulk value (~40 K), and the presence of magnetic ordering in its so-called paramagnetic region (i.e. above 66 K),. The ferrimagnetic nature of both core and shell has been found from the neutron diffraction study. The origin of these two features of magnetic proximity effect has been ascribed to the proximity of gamma-Mn2O3 shell with a high-Tc Fe3O4 core (~858 K in bulk form), and an interface exchange coupling between core and shell. Interestingly, we did not observe any exchange bias effect, which has been interpreted as a signature of a weak interface exchange coupling between core and shell. The present study brings out the importance of the relative strength of the interface coupling in governing the simultaneous occurrence of magnetic proximity effect, and exchange bias phenomenon in a single system.
We have observed conventional signatures of exchange bias (EB), in the form of a shift in the fie... more We have observed conventional signatures of exchange bias (EB), in the form of a shift in the field-cooled hysteresis loop, and a training effect, in BiFe0.8Mn0.2O3 nanoparticles. From neutron diffraction, thermoremanent magnetization, and isothermoremanent magnetization measurements, the nanoparticles are found to be core shell in nature, consisting of an antiferromagnetic (AFM) core, and a two-dimensional diluted AFM (DAFF) shell with a net magnetization under a field. The analysis of the training effect data using Binek's model shows that the observed loop shift arises entirely due to an interface exchange coupling between the core and shell, and the intrinsic contribution of the DAFF shell to the total loop shift is zero. A significantly high value of the EB field has been observed at room temperature. The present study is useful to understand the origin of EB in other DAFF-based systems as well.