Jincang Zhang

Observation of exchange bias in the martensitic state of Ni50Mn36Sn14 Heusler alloy

Exchange bias was observed in the Ni50Mn36Sn14 Heusler alloy after field cooling by means of hysteresis loop measurement. The hysteresis loops shift along the axis of an applied field and its magnitude significantly increased with decreasing temperature below 70K. This effect could be understood as a result of exchange anisotropy created at the interface between an antiferromagnet and a ferromagnet in the phase separated of martensitic state. Above 70K, however, the exchange bias field disappeared and the coercivity significantly reduced owing to the fact that the pinning between an antiferromagnet and a ferromagnet becomes weaker with increasing temperature.

Magnetization reversal and Yb3+/Cr3+ spin ordering at low temperature for perovskite YbCrO3 chromites

The temperature dependence of the dc magnetization and the specific heat capacity are systematically investigated for the perovskite YbCrO3 chromites. The results show that there exist two complex sequences of magnetic transitions with the characteristics of magnetization reversal and Yb3+/Cr3+ spin ordering at different temperature, respectively. The antiferromagneticlike transition around TN=118 K is attributed to the antiferromagnetic ordering of the Cr3+ spins and a negative magnetization, accompanied with a tendency to the plateau below 10 K caused by the Yb3+ ordering. We obtain the Weiss constant of −197.0 K and an effective moment of 5.99μB for the sum of the free ion values of 4.53μB for Yb3+ and 3.87μB for high-spin Cr3+ from the experiments, which shows an antiferromagnetic interaction and the existence of weak canted antiferromagnetic (CAFM) characteristics. Corresponding to the magnetic phase transition in the Cr sublattice, the specific heat capacity under zero fields exhibits a sharp λ-shap...

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.

Weak exchange effect and large refrigerant capacity in a bulk metallic glass Gd0.32Tb0.26Co0.20Al0.22

The magnetic behavior and refrigeration capacity of Gd0.32Tb0.26Co0.20Al0.22, a bulk metallic glass (BMG) fabricated by a copper-mold suck-casting method, are investigated. The Curie temperature increases from 79 K at 200 Oe to 95 K at 50 000 Oe. A weak exchange field of 25 T in the BMG system, caused by the strong disorder, is derived by the mean-field approximation. The maximum magnetic entropy change (8.02 J kg−1 K−1) and the refrigerant capacity (642 J kg−1) for 5 T indicate the BMG has the better refrigerant efficiency compared to known magnetic refrigerants.

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.

Experimental study on impact-initiated characters of multifunctional energetic structural materials

Multifunctional energetic structural materials (MESMs) are a new class of energetic materials, which release energy due to exothermic chemical reactions initiated under shock loading conditions. In order to analyze the impact-initiated process of MESMs, a quasi-sealed test chamber, which was originally developed by Ames [“Vented chamber calorimetry for impact-initiated energetic materials,” in AIAA (American Institute of Aeronautics and Astronautics, 2005), p. 279], is used to study on shock-induced chemical reaction characters at various impact velocities. The impact initiated experiments are involving two typical MESMs, Al/PTFE (polytetrafluoroethylene), W/Zr and inert 2024 Al fragment. The video frames recorded from reactive and inert material impact events have shown the process of late-time after burn phenomena. The total pressure and shock wave reflection at the wall of the test chamber are measured using high frequency gauges. The quasi-pressures inside the test chamber, which is fitting from the t...

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.

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.

The role of 4f-electron on spin reorientation transition of NdFeO3: A first principle study

Magnetic properties and electronic structures of NdFeO3 have been studied by performing accurate first principle calculation based on density functional theory. The 4f-electrons of Nd are explicitly treated as valence electrons. The simulation results of crystal structure and magnetic structure of this compound agree well with the experimental observations. Importantly, our study indicates that the spin reorientation transition of Fe3+ spin sublattice can be ascribed to the exchange interaction between Nd-4f and Fe-3d electrons, which are mediated by O2-2p state in Fe-O plane. As the temperature decreases, the Fe-O and Nd-O bonds become more covalent, and the exchange interactions become stronger.