Baojuan Kang

Temperature induced spin switching in SmFeO3 single crystal.

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.

Magnetization switching of rare earth orthochromite CeCrO3

We report the synthesis of single phase rare earth orthochromite CeCrO3 and its magnetic properties. A canted antiferromagnetic transition with thermal hysteresis at T = 260 K is observed, and a magnetic compensation (zero magnetization) near 133 K is attributed to the antiparallel coupling between Ce3+ and Cr3+ moments. At low temperature, field induced magnetization reversal starting from 43 K for H = 1.2 kOe reveals the spin flip driven by Zeeman energy between the net moments and the applied field. These findings may find potential uses in magnetic switching devices such as nonvolatile magnetic memory which facilitates two distinct states of magnetization.

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

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.

Large rotating field entropy change in ErFeO3 single crystal with angular distribution contribution

We report the rotating field entropy of ErFeO3 single-crystal in a temperature range of 3–40 K. The giant magnetic entropy change, ΔSM = −20.7 J/(kg K), and the refrigerant capacity, RC = 273.5 J/kg, are observed near T=6 K. The anisotropic constants at 6 K, K1 = 1.24× 103 J/kg, K2 = 0.74 × 103 J/kg, in the bc plane are obtained. By considering the magnetocrystalline anisotropy and Fermi-Dirac angular distribution along the orientation of spontaneous magnetization, the experimental results can be well simulated. Our present work demonstrates that ErFeO3 crystal may find practical use for low temperature anisotropic magnetic refrigeration.

Magnetic properties of NdFeO3 single crystal in the spin reorientation region

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.

Strongly enhanced antiferromagnetism and giant spontaneous exchange bias in Ni50Mn36Co4Sn10 Heusler alloy

An enormous spontaneous exchange bias (EB) was obtained after zero-field cooling in Ni50Mn36Co4Sn10 Heusler alloy. It can be attributed to the enhancement of antiferromagnetism, which induces a strong interaction with superferromagnetism, superspin glass, and superparamagnetism. In addition, the EB with an abrupt drop below the lower temperature of 5 K was observed, which can be interpreted as the fact that the rotation of the antiferromagnetic spins from a disordered state to a more ordered state is hindered by domain wall pinning.

Martensitic phase transition, inverse magnetocaloric effect, and magnetostrain in Ni50Mn37-xFexIn13 Heusler alloys

In this paper, we have performed the martensitic phase transition, inverse magnetocaloric effect, and magnetostrain in Ni50Mn37-xFexIn13 (x = 1–4) Heusler alloys. Experimental results indicate that the martensitic phase transition temperature in these materials decreases dramatically with increasing Fe substitution for Mn, which can be explained by the hybridization between Ni and Mn atoms. Large magnetic entropy for Ni50Mn35Fe2In13 could be achieved above room temperature under the applied magnetic field up to 80 kOe. In addition, an enhanced magnetostrain (0.28%) at 110 K associated with the phase transition in Ni50Mn33Fe4In13 was observed after the martensitic phase transformation induced by demagnetization at 100 K. The reason for the enhanced strain has been discussed in detail.

Enhanced 4f-3d interaction by Ti-doping on the magnetic properties of perovskite SmFe1−xTixO3

We report the Ti-doping effects on the total magnetization of perovskite SmFe1−xTixO3 samples with x = 0, 0.1, 0.2, and 0.3. X-ray diffraction and Raman spectroscopy studies indicate that with the increase of Ti doping concentration, the lattice parameter b decreases and the oxygen octahedron is compressed along b axis. Such lattice distortion is also reflected by the changes of antisymmetric stretching mode and symmetric stretching mode of the oxygen octahedron through Raman spectra measurement. An enhancement of the interaction between Sm-4f and Fe-3d electrons is observed due to Ti-doping. This strong interplay between Sm-4f and Fe-3d electrons weakens the total magnetization and considerably suppresses the weak ferromagnetism of Fe sublattice starting from 260 K.

Increased ferromagnetic resonance linewidth and exchange anisotropy in NiFe/FeMn bilayers

In the past investigations, the exchange-biased bilayers show much larger ferromagnetic resonance (FMR) linewidth than that of single ferromagnetic layer films. However, the mechanism of the large linewidth remains controversial. In this paper, the FMR linewidths of NiFe/FeMn bilayers prepared by dc magnetron sputtering system are systematically studied. Besides the intrinsic damping and magnetic inhomogeneity, the extrinsic relaxation based on two-magnon scattering process should be also considered to explain the strong in-plane angular dependence of the linewidths. The fitting of the out-of-plane angular dependence of the linewidths shows that the intrinsic Gilbert damping effect plays a major role in the increased linewidth in the bilayers. The value of the g factor increases due to the effect of the exchange coupling at the NiFe/FeMn interface, resulting in an enhancement in the Gilbert damping factor G. The fitting results indicate that the line broadening of the exchange-biased films is related to t...

A large and reproducible metamagnetic shape memory effect in polycrystalline Ni45Co5Mn37In13 Heusler alloy

We present a detailed study of strain behavior associated with martensitic transition in polycrystalline Ni45Co5Mn37In13 Heusler alloy. A spontaneous phase transition strain with the value of about 0.4% in this alloy can be acquired by applying and removing magnetic field, exhibiting a large two-way metamagnetic shape memory effect (MSME) with nonprestrain. This effect is originated from magnetoelastic coupling due to a large difference in Zeeman energy between austenitic and martensitic phases. In addition, it was also found that even after three magnetic field cycles at 320 K, the two-way MSME is still reproducible. Such characteristic could be ascribed to a random orientation of martensite variants in present alloy.