Journal ArticleDOI

# Temperature dependent structural studies on the spin correlated system A2FeCoO6 (A= Sm, Eu, Dy and Ho) using synchrotron radiation

23 Feb 2017-AIP Advances (AIP Publishing LLCAIP Publishing)-Vol. 7, Iss: 5, pp 055826

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.

AbstractThe 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.

12 citations

Journal ArticleDOI
G. R. Haripriya
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$_6$.

7 citations

Journal ArticleDOI
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.
Abstract: We report the results of our investigation of the physical properties of mixed metal oxides RFe0.5Cr0.5O3 (R = Er and Yb). ErFe0.5Cr0.5O3 undergoes an antiferromagnetic ordering around 270 K followed by spin reorientation (SR) transitions around 150 and 8 K respectively. In contrast, in YbFe0.5Cr0.5O3 a single SR transition is noted at 36 K, below the AFM ordering temperature of 280 K. In ErFe0.5Cr0.5O3, a significant value of magnetic entropy change ( Δ S M ) ∼ -12.4 J/kg-K is noted near the 2nd SR transition, however, this value is suppressed in YbFe0.5Cr0.5O3. Temperature dependent dielectric permittivity of ErFe0.5Cr0.5O3 and YbFe0.5Cr0.5O3 at different frequencies, reveal the presence of Debye-like relaxation behaviour in both compounds, which can be due to the effect of charge carrier hopping between localized states of Fe and Cr ions. Temperature dependent Raman scattering studies divulge that spin-phonon coupling plays a crucial role in defining the physical properties of these compounds.

4 citations

Journal ArticleDOI
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.

3 citations

Proceedings ArticleDOI
10 Apr 2018
TL;DR: In this article, the authors presented the dielectric response of the magnetic perovskite Eu2FeCoO6 from impedance spectroscopy measurements and inferred the two-step relaxation process from Arrhenius fit.
Abstract: The rare earth based transition metal perovskites are well known for their tunable physical properties. Here we present the dielectric response of the magnetic perovskite Eu2FeCoO6 from impedance spectroscopy measurements. The compound having a weak ferromagnetic ground state, is subjected to impedance spectroscopy measurements through the frequency range 100 Hz to 10 MHz for the temperature range 123 K-473 K. The dielectric permittivity shows huge values at high temperatures with low frequency. The two step relaxation process is inferred from Arrhenius fit.The rare earth based transition metal perovskites are well known for their tunable physical properties. Here we present the dielectric response of the magnetic perovskite Eu2FeCoO6 from impedance spectroscopy measurements. The compound having a weak ferromagnetic ground state, is subjected to impedance spectroscopy measurements through the frequency range 100 Hz to 10 MHz for the temperature range 123 K-473 K. The dielectric permittivity shows huge values at high temperatures with low frequency. The two step relaxation process is inferred from Arrhenius fit.

2 citations

##### References
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TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
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Journal ArticleDOI
Hideki Kuwahara
10 Nov 1995-Science
TL;DR: In this article, an electronic phase transition of the first order, which can be caused by an external magnetic field, was discovered in Nd 1/2 Sr 1 /2 MnO 3, where the hysteretic field region was observed to depend critically on temperature and to drastically expand with a decrease of temperature.
Abstract: An electronic (metal-to-insulator) phase transition of the first order, which can be caused by an external magnetic field, was discovered in Nd 1/2 Sr 1/2 MnO 3 . A clear hysteresis was observed during the increase and decrease of an external magnetic field at a fixed temperature. The hysteretic field region was observed to depend critically on temperature and to drastically expand with a decrease of temperature, perhaps as a result of suppression of the effect of thermal fluctuations on the first-order phase transition. Although it has seldom been observed, this is thought to be a generic feature of the first-order phase transition at low temperatures near 0 kelvin.

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Abstract: Electron doping in the ferromagnetic and metallic double perovskites ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ is achieved via the partial substitution of ${\mathrm{Sr}}^{2+}$ by ${\mathrm{La}}^{3+}.$ We show that this doping promotes an extraordinary rising of the Curie temperature of about 70 K above that of the pristine compound. This finding reveals that the ferromagnetic coupling is mediated by itinerant carriers, thus providing solid experimental support to the double-exchange picture for the magnetic interactions. The observation that ${T}_{C}$ can be substantially enhanced may be of relevance for technological applications of these materials in advanced spin devices.

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Abstract: Rare-earth orthoferrites RFeO3 are gifted with fantastic magnetic properties. They have become a research focus for developing multiferroics in recent years. However, it is difficult to obtain pure-phase RFeO3 from the high-temperature synthesis methods. In this work, we report hydrothermal synthesis of well-crystallized pure-phase orthoferrites RFeO3 (R = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) in low temperatures. Structures, morphologies and magnetic properties of the products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), magnetic property measurement system (MPMS), vibrating sample magnetometer (VSM), etc. The expected products were determined to be orthorhombic crystals of perovskite structure. The influences of alkalinity, reaction temperature and time on the formation and growth of RFeO3 crystals were investigated in details, and a dissolution–precipitation mechanism was proposed for describing the formation and growth. Optimum hydrothermal conditions for synthesizing orthoferrites RFeO3 were concluded. The magnetic properties were systematically characterized and studied, including antiferromagnetic transition of Fe (TN1), spin reorientation (TSR), compensation effect (Tcomp), ordering of R (TN2), etc. The relation between the magnetic properties of RFeO3 and the ionic radii of R was investigated and discussed. The experimental results in this work may provide fundamental support to the research and development of multiferroic materials.

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