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: In this paper, the exchange bias and memory effect in double perovskite Sr2FeCoO6 was observed and the spin glass transition temperature, Tg, versus Hdc2/3, followed the Almeida-Thouless line yielding a freezing temperature of Tf=73K.
Abstract: We report on the observation of exchange bias (EB) and memory effect in double perovskite Sr2FeCoO6. Antiphase boundaries between the ferromagnetic and the antiferromagnetic regions in the disordered glassy phase are assumed as responsible for the observed effect, which reflects in the cooling field dependence and temperature evolution of exchange bias field and in training effect. The spin glass (SG) phase itself is characterized through memory, ageing, and magnetic relaxation experiments. The spin glass transition temperature, Tg, versus Hdc2/3 follows the Almeida-Thouless line yielding a freezing temperature, Tf=73K. Time-dependent magnetic relaxation studies reveal the magnetization dynamics of the underlying glassy phase in this double perovskite.
59 citations
TL;DR: In this paper, the magnetic relaxation properties of phase-separated manganite compounds were studied and a series of polycrystalline samples was prepared with different sintering temperatures, resulting in a continuous variation of phase fraction between metallic (ferromagnetic) and charge-ordered phases at low temperatures.
Abstract: We have studied the magnetic relaxation properties of the phase-separated manganite compound ${\mathrm{La}}_{0.250}{\mathrm{Pr}}_{0.375}{\mathrm{Ca}}_{0.375}{\mathrm{MnO}}_{3}.$ A series of polycrystalline samples was prepared with different sintering temperatures, resulting in a continuous variation of phase fraction between metallic (ferromagnetic) and charge-ordered phases at low temperatures. Measurements of the magnetic viscosity show a temperature and field dependence which can be correlated to the static properties. Common to all the samples, there appears to be two types of relaxation processes: at low fields associated with the reorientation of ferromagnetic domains and at higher fields associated with the transformation between ferromagnetic and nonferromagnetic phases.
56 citations
TL;DR: In this paper, the exchange bias and memory effect in double perovskite was observed and the spin glass transition temperature was characterized through memory, ageing and magnetic relaxation experiments, which reflected in the cooling field dependence and temperature evolution of exchange bias field and in training effect.
Abstract: We report on the observation of exchange bias and memory effect in double perovskite Sr$_2$FeCoO$_6$. Antiphase boundaries between the ferromagnetic and antiferromagnetic regions in the disordered glassy phase is assumed as responsible for the observed effect which reflects in the cooling field dependence and temperature evolution of exchange bias field and in training effect. The spin glass phase itself is characterized through memory, ageing and magnetic relaxation experiments. The spin glass transition temperature, $T_g$, versus $H_{dc}^{2/3}$ follows the Almeida-Thouless line yielding a freezing temperature, $T_f$ = 73 K. Time-dependent magnetic relaxation studies reveal the magnetization dynamics of the underlying glassy phase in this double perovskite.
51 citations
TL;DR: In this paper, a spin glass state is observed in the double perovskite oxide Sr2FeCoO6 prepared through sol-gel technique, which shows that the compound crystallizes in tetragonal I4/m structure with lattice parameters.
Abstract: A spin glass state is observed in the double perovskite oxide Sr2FeCoO6 prepared through sol-gel technique. Initial structural studies using x rays reveal that the compound crystallizes in tetragonal I4/m structure with lattice parameters, a = 5.4609(2) A and c = 7.7113(7) A. The temperature dependent powder x ray diffraction data reveal no structural phase transition in the temperature range 10-300 K. However, the unit cell volume shows an anomaly coinciding with the magnetic transition temperature thereby suggesting a close connection between lattice and magnetism. Neutron diffraction studies and subsequent bond valence sums analysis show that in Sr2FeCoO6, the B site is randomly occupied by Fe and Co in the mixed valence states of Fe3 + /Fe4+ and Co3+/Co4+. The random occupancy and mixed valence sets the stage for inhomogeneous magnetic exchange interactions and in turn, for the spin glass state in this double perovskite, which is observed as an irreversibility in temperature dependent dc magnetization at Tf ∼ 75 K. Dynamical scaling analysis of χ′(T) yields a critical temperature Tct = 75.14(8) K and an exponent zν = 6.2(2) typical for spin glasses. The signature of presence of mixed magnetic interactions is obtained from the thermal hysteresis in magnetization of Sr2FeCoO6. Combining the neutron and magnetization results of Sr2FeCoO6, we deduce that Fe is in low spin state while Co is in both low spin and intermediate spin states.
49 citations
TL;DR: In this paper, the spin glass state in the double perovskite oxide Sr$2}$FeCoO$6}$ was observed through sol-gel technique and the properties of the compound were investigated.
Abstract: We report the observation of spin glass state in the double perovskite oxide Sr$_{2}$FeCoO$_{6}$ prepared through sol-gel technique. Initial structural studies using x rays reveal that the compound crystallizes in tetragonal $I 4/m$ structure with lattice parameters, $a$ = 5.4609(2) \AA and $c$ = 7.7113(7) \AA. The temperature dependent powder x ray studies reveal no structural phase transition in the temperature range 10 -- 300 K. However, the unit cell volume shows an anomaly coinciding with the magnetic transition temperature thereby suggesting a close connection between lattice and magnetism. Neutron diffraction studies and subsequent bond valence sums analysis show that in Sr$_{2}$FeCoO$_{6}$, the $B$ site is randomly occupied by Fe and Co in the mixed valence states of Fe$^{3+}$/Fe$^{4+}$ and Co$^{3+}$/Co$^{4+}$. The random occupancy and mixed valence sets the stage for inhomogeneous magnetic exchange interactions and in turn, for the spin glass like state in this double perovskite which is observed as an irreversibility in temperature dependent dc magnetization at $T_f\sim$ 75 K. Thermal hysteresis observed in the magnetization profile of Sr$_{2}$FeCoO$_{6}$ is indicative of the mixed magnetic phases present. The dynamic magnetic susceptibility displays characteristic frequency dependence and confirms the spin glass nature of this material. Dynamical scaling analysis of $\chi'(T)$ yields a critical temperature $T_{ct}$ = 75.14(8) K and an exponent $z
u$ = 6.2(2) typical for spin glasses. The signature of presence of mixed magnetic interactions is obtained from the thermal hysteresis in magnetization of Sr$_{2}$FeCoO$_{6}$. Combining the neutron and magnetization results of Sr$_2$FeCoO$_6$, we deduce the spin states of Fe to be in low spin while that of Co to be in low spin and intermediate spin.
48 citations