Dielectric and optical phonon anomalies near antiferromagnetic ordering in LaCrO3: A possible near room temperature magnetodielectric system
TL;DR: In this paper, anomalies in the dielectric and optical phonon spectra in bulk orthorhombic distorted perovskite LaCrO3 near an antiferromagnetic transition at 290
Abstract: We report on anomalies in the dielectric and optical phonon spectra in bulk orthorhombic distorted perovskite LaCrO3 near an antiferromagnetic transition at 290 K. These anomalies were tracked using temperature dependent (200 K–320 K) dielectric and Raman spectroscopy. We observed a blue-shift for the B3g(3) optical phonon mode coincident with the onset of antiferromagnetic ordering of LaCrO3 in conjunction with a broad dielectric anomaly near the Neel temperature. The dielectric and optical phonon anomalies are discussed in the context of the observed antiferromagnetic transition in temperature dependent magnetic studies.
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TL;DR: In this paper, a solgel-based synthesis of DyFe0.5Cr 0.5O3 has been proposed to obtain high-temperature multiferroicity and large magnetocaloric effect (MCE) for practical applications.
Abstract: DyFe0.5Cr0.5O3 has been synthesized using a sol-gel method. It exhibits ferroelectricity at the antiferromagnetic ordering temperature TN1∼261 K. Large magnetocaloric effect (MCE) (11.3 J/kg K at 4.5 T) enhanced by magnetoelectric coupling due to magnetic field and temperature induced magnetic transition was observed. Temperature-dependent Raman study shows an anomalous behavior near TN1 in the phonon modes related to the vibration of Dy atoms and stretching of CrO6/FeO6 octahedra, suggesting the ferroelectricity in DyFe0.5Cr0.5O3 is associated with the spin-phonon coupling with respect to both Dy and Cr/Fe ions. These results suggest routes to obtain high-temperature multiferroicity and large MCE for practical applications.
82 citations
01 Feb 2015
TL;DR: The magnetic properties of bulk LaCrO3, a GdFeO3-type distorted perovskite, with a predominant antiferromagnetic phase transition at?290 K was studied in this article.
Abstract: We studied magnetic properties of bulk LaCrO3; a GdFeO3-type distorted perovskite, with a predominant antiferromagnetic phase transition at ?290 K. The bulk LaCrO3 exhibits intrinsic weak ferromagnetism at room temperature, which may arise due to the tilting of CrO6 octahedra, resulting in a non-zero net magnetic moment, as confirmed from the magnetization measurements. A broad magnetically-induced entropy change (??S) is observed with the maxima at 290 K, close to room temperature in LaCrO3 system.
24 citations
TL;DR: In this article, a comprehensive investigation of dielectric and magnetic phase transitions in Yb(Fe0.5Cr 0.5)O3 bulk ceramics has been presented.
Abstract: A comprehensive investigation of dielectric and magnetic phase transitions in Yb(Fe0.5Cr0.5)O3 bulk ceramics has been presented. The co-existence of orthorhombic phase (Pbnm) along with minor hexagonal (P63cm) phase is detected through Rietveld refinement technique, whereas the presence of Fe3+/Fe2+ and Cr3+/Cr2+ species is also encountered under XPS study. The dielectric broad-band spectroscopic study (5–500 K) reveals that two dielectric transition peaks: (1) at 370 K, first order ferroelectric transition for induced local non-centrosymmetry, and (2) at 462 K, diffuse like relaxor transition because of formation of polar nano-regions and, Schottky barriers at sample-electrode interface, respectively. The complex impedance spectroscopic study exhibits the non-Debye type dielectric relaxation phenomena at lower temperatures, while at high temperatures, oxygen ion vacancies are found to contribute the conduction progression. Furthermore, dc-magnetization plot in FC-ZFC mode detects the strong interactions between Cr3+/Fe3+sublattices also with Yb3+ ions and Yb3+–Yb3+ ions. This results into an antiferromagnetic ordering at TN ~271 K for Cr3+–Cr3+/Fe3+–Fe3+ or Cr3+–Fe3+ spins followed by weak ferromagnetic ordering at 41 K for the occurrence of progressive spin reorientation and further at 11.2 K due to onset interactions of ferromagnetic Cr3+/Fe3+ sub-lattices with paramagnetic Yb3+ ions.
23 citations
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TL;DR: In this article, the authors studied the magnetic properties of bulk LaCrO3, a GdFeO3-type distorted perovskite, with a predominant antiferromagnetic phase transition at ~ 290 K.
Abstract: We studied the magnetic properties of bulk LaCrO3; a GdFeO3-type distorted perovskite, with a predominant antiferromagnetic phase transition at ~ 290 K. The bulk LaCrO3 exhibits intrinsic weak ferromagnetism at room temperature, which may arise due to the tilting of CrO6 octahedra, resulting in a non-zero net magnetic moment, as confirmed from the magnetization measurements. A broad magnetically-induced entropy change (-{\Delta}S) is observed with the maximum at 290 K, close to room temperature in LaCrO3 system.
22 citations
TL;DR: In this paper, the structural, magnetic, and magnetoelectric properties of DyCr0.5Mn 0.5O3 were investigated and it was shown that the ferroelectricity in DyCr 0.1.5 mn 0 o3 is driven by magnetic order.
15 citations
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TL;DR: In this paper, the Anderson theory of superexchange was extended to include spin-orbit coupling and the antisymmetric spin coupling suggested by Dzialoshinski from purely symmetry grounds and the symmetric pseudodipolar interaction were derived.
Abstract: A theory of anisotropic superexchange interaction is developed by extending the Anderson theory of superexchange to include spin-orbit coupling. The antisymmetric spin coupling suggested by Dzialoshinski from purely symmetry grounds and the symmetric pseudodipolar interaction are derived. Their orders of magnitudes are estimated to be ($\frac{\ensuremath{\Delta}g}{g}$) and ${(\frac{\ensuremath{\Delta}g}{g})}^{2}$ times the isotropic superexchange energy, respectively. Higher order spin couplings are also discussed. As an example of antisymmetric spin coupling the case of Cu${\mathrm{Cl}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O is illustrated. In Cu${\mathrm{Cl}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O, a spin arrangement which is different from one accepted so far is proposed. This antisymmetric interaction is shown to be responsible for weak ferromagnetism in $\ensuremath{\alpha}$-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$, MnC${\mathrm{O}}_{3}$, and Cr${\mathrm{F}}_{3}$. The paramagnetic susceptibility perpendicular to the trigonal axis is expected to increase very sharply near the N\'eel temperature as the temperature is lowered, as was actually observed in Cr${\mathrm{F}}_{3}$.
5,322 citations
TL;DR: In this article, the most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned, and a review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data.
Abstract: This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.
3,926 citations
TL;DR: The discovery of ferroelectricity in a perovskite manganite, TbMnO3, where the effect of spin frustration causes sinusoidal antiferromagnetic ordering and gigantic magnetoelectric and magnetocapacitance effects are found.
Abstract: The magnetoelectric effect--the induction of magnetization by means of an electric field and induction of polarization by means of a magnetic field--was first presumed to exist by Pierre Curie, and subsequently attracted a great deal of interest in the 1960s and 1970s (refs 2-4). More recently, related studies on magnetic ferroelectrics have signalled a revival of interest in this phenomenon. From a technological point of view, the mutual control of electric and magnetic properties is an attractive possibility, but the number of candidate materials is limited and the effects are typically too small to be useful in applications. Here we report the discovery of ferroelectricity in a perovskite manganite, TbMnO3, where the effect of spin frustration causes sinusoidal antiferromagnetic ordering. The modulated magnetic structure is accompanied by a magnetoelastically induced lattice modulation, and with the emergence of a spontaneous polarization. In the magnetic ferroelectric TbMnO3, we found gigantic magnetoelectric and magnetocapacitance effects, which can be attributed to switching of the electric polarization induced by magnetic fields. Frustrated spin systems therefore provide a new area to search for magnetoelectric media.
3,769 citations
TL;DR: Insulator-metal phenomena depending on band filling, temperature, and external magnetic field have been investigated for prototypical double-exchange ferromagnets, namely, crystals of crystals of La 1-x, showing large negative magnetoresistance around the ferromagnetic transition temperature.
Abstract: Insulator-metal phenomena depending on band filling (doping degree), temperature, and external magnetic field have been investigated for prototypical double-exchange ferromagnets, namely, crystals of ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ (0\ensuremath{\le}x\ensuremath{\le}0.6). The electronic phase diagram in the plane of the temperature vs nominal hole concentration (x) has been deduced from the magnetic and electrical measurements on the melt-grown crystals. Around the ferromagnetic transition temperature ${\mathit{T}}_{\mathit{C}}$, large negative magnetoresistance was observed. Irrespective of temperature, reduction of the resistivity is scaled with the field-induced magnetization (M) as -\ensuremath{\Delta}\ensuremath{\rho}/\ensuremath{\rho}=C(M/${\mathit{M}}_{\mathit{s}}$${)}^{2}$ for M/${\mathit{M}}_{\mathit{s}}$\ensuremath{\lesssim}0.3, where ${\mathit{M}}_{\mathit{s}}$ is the saturated magnetization. The coefficient C strongly depends on x, i.e., C\ensuremath{\approxeq}4 near the compositional insulator-metal phase boundary (${\mathit{x}}_{\mathit{c}}$\ensuremath{\sim}0.17), but decreases down to \ensuremath{\approxeq}1 for xg=0.4, indicating the critical change of the electronic state.
2,412 citations
TL;DR: In this article, the experimental studies of displacive phase transitions in solids are summarized, focusing on inelastic light scattering and neutron scattering; related infrared reflectivity measurements, as well as x-ray and EPR analyses are also summarized.
Abstract: This paper reviews the experimental studies of displacive phase transitions in solids. Primary emphasis is upon inelastic light scattering and neutron scattering; related infrared reflectivity measurements, as well as x-ray and EPR analyses are also summarized. Several prototype structures are considered in detail: (1) the rocksalt IV-VI semiconductors PbTe, SnTe, and GeTe; (2) the ferroelectric perovskites exemplified by PbTi${\mathrm{O}}_{3}$ and BaTi${\mathrm{O}}_{3}$; (3) perovskites which exhibit cell-doubling transitions, such as LaAl${\mathrm{O}}_{3}$, SrTi${\mathrm{O}}_{3}$, and KMn${\mathrm{F}}_{3}$; (4) crystals having the $\ensuremath{\alpha}$-quartz structure, including Ge${\mathrm{O}}_{2}$, Si${\mathrm{O}}_{2}$, and AlP${\mathrm{O}}_{4}$; (5) the "improper ferroelectrics" ${\mathrm{Gd}}_{2}$${(\mathrm{M}\mathrm{o}{\mathrm{O}}_{4})}_{3}$ and ${\mathrm{Tb}}_{2}$${(\mathrm{M}\mathrm{o}{\mathrm{O}}_{4})}_{3}$; (6) the V-VI-VII semiconductors typified by SbSI; (7) the hydrogen-bonded ferroelectrics of the K${\mathrm{H}}_{2}$P${\mathrm{O}}_{4}$ family; (8) Jahn-Teller systems such as DyV${\mathrm{O}}_{4}$ and RbCo${\mathrm{F}}_{3}$, in which structural distortions occur as secondary effects; (9) order-disorder systems such as NaN${\mathrm{O}}_{2}$ and the ammonium halides (N${\mathrm{H}}_{4}$Cl, N${\mathrm{H}}_{4}$Br), in which no "soft mode" occurs in the spectral region ($\ensuremath{\omega}g{10}^{11}$ Hz) probed by ir, Raman, and neutron spectroscopy; (10) $\ensuremath{\beta}$-tungsten ($A\ensuremath{-}15$) structures such as ${\mathrm{V}}_{3}$Si and ${\mathrm{Nb}}_{3}$Sn, which exhibit high-temperature superconductivity. These crystal categories are used to illustrate several phenomena of current physical interest: Specifically, we discuss harmonic and anharmonic mode coupling; "critical exponents" $\ensuremath{\beta}$ differing from one-half in the temperature dependences of the order parameter $\ensuremath{\phi}(T)={\ensuremath{\phi}}_{0}{(T\ensuremath{-}{T}_{0})}^{\ensuremath{\beta}}$ and of the soft-mode frequency $\ensuremath{\omega}(T)={\ensuremath{\omega}}_{0}{(T\ensuremath{-}{T}_{0})}^{\ensuremath{\beta}}$; and the recently discovered "central" modes centered at zero frequency, which grow in intensity as the transition temperature ${T}_{0}$ is approached from above or below. The review covers the period 1940-1972. A few 1973 works are mentioned for which the author had preprints in 1972 or very early 1973. This review is in no sense a comprehensive survey of ferroelectricity. Readers are referred to the following earlier reviews on that subject: Silverman (1966, 1969), Cochran and Cowley (1967), Blinc (1968), Murzin et al. (1968), Nettleton (1970), and Blinc and Zaks (1972).
639 citations