Hydrothermal synthesis and magnetic properties of multiferroic rare-earth orthoferrites

We present an overview of the current interest in non-collinear magnetism in multiferroic perovskite crystals. We first describe the different microscopic mechanisms giving rise to the non-collinearity of spins in this class of materials. We discuss, in particular, the interplay between non-collinear magnetism and ferroelectric and antiferrodistortive distortions of the perovskite structure, and how this can promote magnetoelectric responses. We then provide a literature survey on non-collinear multiferroic perovskites. We discuss numerous examples of spin cantings driving weak ferromagnetism in transition metal perovskites, and of spin-induced ferroelectricity as observed in the rare-earth based perovskites. These examples are chosen to best illustrate the fundamental role of non-collinear magnetism in the design of multiferroicity.

https://iopscience.iop.org/article/10.1088/0953-8984/28/12/123001/pdf

Non-collinear magnetism in multiferroic perovskites.

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.

Multiferroicity and magnetoelectric coupling enhanced large magnetocaloric effect in DyFe0.5Cr0.5O3

In this work, a polycrystalline bulk DyCrO3 sample was prepared by a solution route and the structural and magnetic properties were investigated. The phase purity and ionic valence state of the DyCrO3 sample were determined by x-ray diffraction/Raman spectroscopy and x-ray photoelectron spectroscopy, respectively. The AC and DC magnetization measurements revealed the onset of antiferromagnetic order at 146 K with an effective moment of 8.88 μB. Isothermal magnetization measurements of this material are presented for the first time, showing a peak in the coercive field at 80 K that is explained by the competition between the paramagnetic Dy3+ and Cr3+ sublattices. DyCrO3 was found to display a large magnetocaloric effect (8.4 J/kg K) and relative cooling power (217 J/kg) at 4 T applied field, which renders DyCrO3 useful for magnetic refrigeration between 5 K and 30 K.

Magnetic and magnetocaloric properties of bulk dysprosium chromite

The spin reorientation of ErFeO3 that spontaneously occurs at low temperature has been previously determined to be a process involving the continuous rotation of Fe3+ spins. In this work, the dynamic process of spin reorientation in ErFeO3 single crystal has been investigated by AC susceptibility measurements at various frequencies and static magnetic fields. Interestingly, two completely discontinuous steps are induced by a relatively large static magnetic field due to the variation in the magnetic anisotropy during this process. It provides deeper insights into the intriguing magnetic exchange interactions which dominate the sophisticated magnetic phase transitions in the orthoferrite systems.

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Magnetic field induced discontinuous spin reorientation in ErFeO3 single crystal

High quality NdFeO3 single crystal has been grown by the four-mirror image floating zone technique. The magnetic properties and specific heat of NdFeO3 single crystal were systematically studied in the temperature range from 2 to 300 K. A clear spin reorientation behavior is observed in a wide temperature range from 100 to 170 K, with the gradual transition of the Fe3+ magnetic moment ordering from {Gz, Mx}-type ordering at low temperatures to {Gx, Mz}-type ordering at high temperatures. In the temperature range from 170 to 300 K, the value of Mx is not equal to zero. It is assumed a single {Gx, Mz}-type ordering mixed with {Gxz, Mxz}-type orderings. During the spin orientation transition process, the hysteresis loops become narrow with very small coercivity. Based on the specific heat measurement, the Schottky anomaly at very low temperature and the thermal anomalies induced by the spin reorientation were also discussed.

Magnetic properties of NdFeO3 single crystal in the spin reorientation region

We report the magnetic and magnetocaloric properties of Dy1−xHoxMnO3 (0 ≤ x ≤ 1). Large entropy change of 12.5 J/kg K and refrigeration capacity of 312 J/kg at 7 T for HoMnO3 is calculated based on isothermal magnetization measurements. The peak temperature of magnetic entropy change for all samples keeps the same 10.5 K, indicating that Ho3+ doping only affects the value of magnetic entropy. An unambiguous intrinsic structural transition near 7 K is first observed by strain measurement, which is believed as the origin of magnetic symmetry transition of Dy1−xHoxMnO3 and induces the magnetocaloric effect with the cooperation interaction between Dy3+/Ho3+and Mn3+ spins.

Mingjie Shao

Papers

Magnetic properties of NdFeO3 single crystal in the spin reorientation region

Large magnetocaloric effect induced by intrinsic structural transition in Dy1−x HoxMnO3

Single crystal growth, magnetic properties and Schottky anomaly of HoFeO3 orthoferrite

Large magnetocaloric effect in HoFeO3 single crystal

Growth rate dependence of the NdFeO3 single crystal grown by float-zone technique