Temperature dependent structural studies on the spin correlated system A2FeCoO6 (A= Sm, Eu, Dy and Ho) using synchrotron radiation
TL;DR: In this paper, temperature dependent structural studies carried out on the spin-correlated system A2FeCoO6 (A= Sm, Eu, Dy and Ho) or AFCO (A = Sm,E, D and H), using synchrotron radiation is presented.
Abstract: The temperature dependent structural studies carried out on the spin-correlated system A2FeCoO6 (A= Sm, Eu, Dy and Ho) or AFCO (A= Sm, E, D and H), using synchrotron radiation is presented. Owing to the large absorption cross-sections of the rare earths; Eu, Sm and Dy for neutrons, synchrotron radiation is one of the best available candidates for probing the system. The perovskite phase formation is inferred from laboratory XRD with Cu Kα source. The temperature dependent synchrotron X-ray diffraction (SXRD) experiments show the coexistence of monoclinic P21/n and orthorhombic Pbnm phases in Ho and Dy, while Eu and Sm are formed in single phase Pbnm. The temperature dependent DC magnetization measurements infer the presence of many interesting features such as thermal hysteresis, magnetic irreversibility, spin re-orientation, re-entrant magnetization and negative magnetization.
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TL;DR: In this paper, the magnetic phase transitions in a double perovskite Ho2FeCoO6 were characterized and studied through magnetization and specific heat, and the magnetic structures were elucidated through neutron powder diffraction.
Abstract: We report the experimental observation of spin reorientation in the double perovskite Ho2FeCoO6. The magnetic phase transitions in this compound are characterized and studied through magnetization and specific heat, and the magnetic structures are elucidated through neutron powder diffraction. Two magnetic phase transitions are observed in this compound-one at K, from paramagnetic to antiferromagnetic, and the other at K, from a phase with mixed magnetic structures to a single phase through a spin reorientation process. The magnetic structure in the temperature range 200–45 K is a mixed phase of the irreducible representations and , both of which are antiferromagnetic. The phase with mixed magnetic structures that exists in Ho2FeCoO6 gives rise to a large thermal hysteresis in magnetization that extends from 200 K down to the spin reorientation temperature. At T N2, the magnetic structure transforms to . Though long-range magnetic order is established in the transition metal lattice, it is seen that only short-range magnetic order prevails in the Ho3+ lattice. Our results should motivate further detailed studies on single crystals in order to explore the spin reorientation process, spin switching and the possibility of anisotropic magnetic interactions giving rise to electric polarization in Ho2FeCoO6.
20 citations
TL;DR: In this paper, the physical properties of mixed metal oxides RFe0.5Cr 0.5O3 (R = Er and Yb) were investigated and a significant value of magnetic entropy change ( Δ S M ) ∼ -12.4 J/kg-K was noted near the 2nd spin reorientation (SR) transition.
12 citations
TL;DR: The experimental observation of spin reorientation in the double perovskite Ho2FeCoO6 is reported, and it is seen that only short-range magnetic order prevails in Ho3+ - lattice.
Abstract: We report the experimental observation of spin reorientation in the double perovskite Ho$_2$FeCoO$_6$. The magnetic phase transitions in this compound are characterized and studied through magnetization and specific heat, and the magnetic structures are elucidated by neutron powder diffraction. Two magnetic phase transitions are observed in this compound - one at $T_\mathrm{N1} \approx$ 250~K, from paramagnetic to antiferromagnetic, and the other at $T_\mathrm{N2} \approx$ 45~K, from a phase with mixed magnetic structures to a single phase through a spin reorientation process. The magnetic structure in the temperature range 200~K - 45~K is a mixed phase of the irreducible representations $\Gamma_1$ and $\Gamma_3$, both of which are antiferromagnetic. The phase with mixed magnetic structures that exists in Ho$_2$FeCoO$_6$ gives rise to a large thermal hysteresis in magnetization that extends from 200~K down to the spin reorientation temperature. At $T_\mathrm{N2}$, the magnetic structure transforms to $\Gamma_1$. Though long-range magnetic order is established in the transition metal lattice, it is seen that only short-range magnetic order prevails in Ho$^{3+}$ - lattice. Our results should motivate further detailed studies on single crystals in order to explore spin reorientation process, spin switching and the possibility of anisotropic magnetic interactions giving rise to electric polarization in Ho$_2$FeCoO$_6$.
10 citations
TL;DR: In this article, the authors present the results on the order of phase transition around the spin re-orientation region using isothermal magnetization data performed on the sol-gel synthesized disordered double perovskite oxides Sm2FeCoO6 and Dy2FeO6 by Arrott plot method.
Abstract: We present the results on the order of phase transition around the spin re-orientation region using isothermal magnetization data performed on the sol-gel synthesized disordered double perovskite oxides Sm2FeCoO6 and Dy2FeCoO6 by Arrott plot method. The temperature variation of the DC magnetization data of both the samples show that there are two magnetic phase transitions; one at high temperature regime, the conventional paramagnetic (PM) to ferro or ferrimagnetic (FM or FIM) and the other at low temperatures, ferro or ferrimagnetic (FM or FIM) to antiferromagnetic (AFM). From the Arrott plot method, it is inferred that spin re-orientation transitions of both the compounds has a first order nature corresponding to the FM (FIM) to AFM transition.
6 citations
TL;DR: In this article, the authors investigated the possible source of weak ferromagnetism and the metamagnetic phase transitions in the antiferromagnetic systems with octahedral structure, such as perovskites.
6 citations
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TL;DR: It is found that the magnetization of single-crystal SmFeO3 can be switched by temperature, and tuning the magnitude of applied magnetic field allows us to realize such spin switching even at room temperature.
Abstract: The prospect of controlling the magnetization (M) of a material is of great importance from the viewpoints of fundamental physics and future applications of emerging spintronics. A class of rare-earth orthoferrites RFeO3 (R is rare-earth element) materials exhibit striking physical properties of spin switching and magnetization reversal induced by temperature and/or applied magnetic field. Furthermore, due to the novel magnetic, magneto-optic and multiferroic properties etc., RFeO3 materials are attracting more and more interests in recent years. We have prepared and investigated a prototype of RFeO3 materials, namely SmFeO3 single-crystal. And we report magnetic measurements upon both field cooling (FC) and zero-field cooling (ZFC) of the sample, as a function of temperature and applied magnetic field. The central findings of this study include that the magnetization of single-crystal SmFeO3 can be switched by temperature and tuning the magnitude of applied magnetic field allows us to realize such spin switching even at room temperature.
176 citations
TL;DR: In this article, two polycrystalline double perovskites with different degrees of antisite disorder were examined by magnetic measurements and neutron powder diffraction techniques in the 15--500 K temperature range.
Abstract: Antisite disordering in ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ double perovskites (containing Mo atoms at Fe positions, and vice versa) has recently been shown to have a dramatic influence in their magnetic and magnetotransport properties. In the present paper, two polycrystalline ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ samples showing different degrees of antisite disorder (a nominally ``ordered'' sample with \ensuremath{\sim}70% of cationic ordering and a nominally ``disordered'' sample with \ensuremath{\sim}18% of cationic ordering) have been examined by magnetic measurements and neutron powder diffraction techniques in the 15--500 K temperature range. Our main finding is that the ``disordered'' sample exhibits a strong magnetic scattering (noticeable even at 500 K), comparable to that displayed by the ``ordered'' one below ${T}_{C}=415\mathrm{K}.$ For the ``disordered'' sample, the magnetic scattering exhibited on low-angle Bragg positions, is not to be ascribed to a (nonexistent) ferrimagnetic ordering: our results suggest that it originates upon naturally occurring groups of Fe cations in which strong antiferromagnetic (AFM) Fe-O-Fe superexchange interactions are promoted, similar to those existing in the ${\mathrm{LaFeO}}_{3}$ perovskite. These Fe groups are not magnetically isolated, but coupled by virtue of Fe-O-Mo AFM interactions, which maintain the long-range coherence of this AFM structure. Susceptibility measurements confirm the presence of AFM interactions below 770 K.
143 citations
TL;DR: Comprehensive temperature scans of the resistivity of a high-quality sample of PrNiO3 were made under different pressures up to 30 kbar; they have revealed that the insulator phase is suppressed completely at P approximately equal to 13 kbar, transforming to a non-Fermi-liquid phase in which theresistivity varies as Deltarho=rho(T)- rho(0) approximately T(n).
Abstract: Comprehensive temperature scans of the resistivity of a high-quality sample of PrNiO3 were made under different pressures up to 30 kbar; they have revealed that the insulator phase is suppressed completely at P approximately equal to 13 kbar, transforming to a non-Fermi-liquid phase in which the resistivity varies as Deltarho=rho(T)-rho(0) approximately T(n) with n=1.33 and 1.60 over a broad pressure range.
76 citations
TL;DR: In this paper, the spontaneous orthorhombic strain and the tilting angle of the CO6 octahedra progressively increase from Pr to Lu due to simple steric factors.
Abstract: RCoO3 perovskites (R = Pr, Tb, Dy, Ho, Er, Tm, Yb, Lu) have been prepared in a polycrystalline form by thermal treatment in air (R = Pr, Tb, Dy), under O2 pressure (200 bar) (R = Ho, Er) or moderate hydrostatic pressures (20 kbar) (R = Tm, Yb, Lu). The samples have been studied at room temperature by high-resolution neutron powder diffraction to follow the evolution of the crystal structures along the series. In all cases, the structure is orthorhombic, space group Pbnm. The spontaneous orthorhombic strain and the tilting angle of the CO6 octahedra progressively increase from Pr to Lu due to simple steric factors. The CoO6 octahedra also undergo a progressive axial deformation along the series, which cannot be ascribed to electronic factors, given the low-spin configuration exhibited at room temperature by Co3+ (t62ge0g) cations for R = Tb…Lu. The stability of the crystal structure is discussed in the light of bond-valence arguments.
65 citations
TL;DR: In this paper, a paramagnetic-ferromagnetic phase transition occurs in the double perovskite Y2CoMnO6 which has been recently identified as a multiferroic.
Abstract: Antisite disorder is observed to have significant impact on the magnetic properties of the double perovskite Y2CoMnO6 which has been recently identified as a multiferroic. A paramagnetic-ferromagnetic phase transition occurs in this material at Tc ≈ 75 K. At 2 K, it displays a strong ferromagnetic hysteresis with a significant coercive field of Hc ≈ 15 kOe. Sharp steps are observed in the hysteresis curves recorded below 8 K. In the temperature range 2 K ≤ T ≤ 5 K, the hysteresis loops are anomalous as the virgin curve lies outside the main loop. The field-cooling conditions as well as the rate of field-sweep are found to influence the steps. Quantitative analysis of the neutron diffraction data shows that at room temperature, Y2CoMnO6 consists of 62% of monoclinic P21/n with nearly 70% antisite disorder and 38% Pnma. The bond valence sums indicate the presence of other valence states for Co and Mn which arise from disorder. We explain the origin of steps by using a model for pinning of magnetization at the antiphase boundaries created by antisite disorder. The steps in magnetization closely resemble the martensitic transformations found in intermetallics and display first-order characteristics as revealed in the Arrott's plots.
62 citations