Zhenjie Feng

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...

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.

Novel Magnetization Induced by Phase Coexistence in Multiferroic HoCrO3 Chromites

Single-phase HoCrO3 samples were prepared using the conventional solid-state reaction. The temperature dependence of dc magnetic properties show that the ZFC and FC magnetization curves are irreversible strongly and nearly symmetrical below 141.0 K under 100 Oe. Moreover, there appears a novel magnetization behavior with negative magnetization (diamagnetism-like) characteristics. This behavior exhibits the coexistence of canted antiferromagnetic and weak ferromagnetic phase and the existence of competition mechanism below Tc1 = 141.0 K. In addition, it is also proved that Ho ion ordered weak CAFM below 7.5 K. The current novel magnetization can be interpreted from the interaction between paramagnetic Ho3+ moments and canted Cr3+ moments.

Magnetic properties of rare earth HoCrO3 chromites

Abstract The temperature dependence of the magnetic properties was systemically studied by dc/ac magnetization and specific heat measurement for heavy rare earth HoCrO 3 chromites. The results revealed the existence of complex phase coexistence and competitive magnetic behavior in HoCrO 3 chromites. It was found that, in the region of higher temperature above 141.0 K, HoCrO 3 behaved as a typical Curie-Weiss paramagnetic (PM). And in the region of low temperature, a novel magnetization behavior was observed with negative magnetization (diamagnetism-like) characteristics under an external field of 100 Oe and M-T curves exhibited two symmetrical branches for field cooling (FC) and zero field cooling (ZFC) modes. This behavior indicated the coexistence of canted antiferromagnetic (CAFM) and weak ferromagnetic (FM) phase. These also exhibited the existence of competition mechanism below characteristic temperature T N1 =141.0 K and the magnetic order of Ho ion below 7.5 K. The current complex magnetization might be attributed to the interaction between paramagnetic Ho 3+ moments and canted Cr 3+ moments.

Cooling field tuned magnetic phase transition and exchange bias-like effect in Y0.9Pr0.1CrO3

Cooling magnetic field dependence of magnetic phase transition has been observed in Y0.9Pr0.1CrO3. GzFx order (spin structure of PrCrO3) is dominant after zero field cooling (ZFC), whereas GxFz order (spin structure of YCrO3) is dominant after cooling under a field higher than 100 Oe. Positive/negative exchange bias-like effect, with large vertical shift and small horizontal shift, has been observed after FC/ZFC process. The vertical shift can be attributed to the frozen ordered Pr3+ and Cr3+ spins in magnetic domains, because of the strong coupling between Pr3+ and Cr3+ sublattices; while the horizontal shift is a result of the pinning of spins at the interfaces. The frozen structure is generated by the field used for the measurement of the initial magnetization curve of M(H) for the ZFC cooled sample, while it is generated by the cooling field for the sample cooled under a cooling field higher than 100 Oe.

Magnetic phase transition and giant anisotropic magnetic entropy change in TbFeO3 single crystal

The magnetocaloric effect (MCE) is an intrinsic property of magnetic materials that enable magnetic refrigeration devices without using the traditional vapour-compression. Temperature sensitive and anisotropic magnetic solids might give rise to a large rotating MCE for building compact and efficient magnetic cooling systems by simply rotating the sample. Here, we report an unprecedented maximal refrigeration capacity of 497.36 J/kg (at 70 kOe) in perovskite TbFeO3 single crystal, resulting from its giant anisotropic magnetic entropy change along a axis. Our paper reveals that interaction between Fe-3d and Tb-4f electrons drives extremely interesting spin reorientation transition, which is highly sensitive to magnetic field and temperature. These findings highlight potential applications of an emerging material for high efficient low temperature magnetic refrigeration, which is compact and quiet, and does not use ozone-depleting coolant gases.

AutoFP: a GUI for highly automated Rietveld refinement using an expert system algorithm based on FullProf

AutoFP, a highly automated software toolkit, has been developed to improve the extent of automation of the widely used Rietveld refinement program FullProf [Rodriguez-Carvajal (1993). Physica B, 192, 55-69]. An expert system algorithm is used as the control layer to simulate the manual process when FullProf is used to perform Rietveld refinement. This enables the program to complete the Rietveld refinement highly automatically. It is shown that the expert system algorithm is a good choice for automating Rietveld refinement. The programming interface is available for advanced users to implement their own acquired experience of refinement or add new Rietveld refinement engines to AutoFP. AutoFP can be also used as an automated Rietveld refinement engine by other programs. AutoFP is an open-source software package developed in Python, and it is user friendly, easy to learn and easy to use.

Magnetic field controllable electric polarization in Y-type hexaferrite Ba0.5Sr1.5Co2Fe12O22

We report the magnetic properties and the magnetoelectric effect in Y-type hexaferrite polycrystalline sample of Ba0.5Sr1.5Co2Fe12O22 (BSCFO). The magnetic critical temperature of BSCFO is 620 K, and the low-temperature helical magnetic order can hold up to 255 K. The isothermal magnetization curves sustain ferromagnetic hysteresis from 10 K to 300 K. Under external magnetic fields, the magnetic field induced electric polarization is observed up to 150 K. The magnitude and the sign of the electric polarization can be controlled by the applied magnetic field. These magnetic and magnetoelectric results provide the promise of the studied new hexaferrite as a potential multiferroic material.

Remarkable magnetic relaxation and metamagnetic transition in phase-separated La0.7Ca0.3Mn0.9Cu0.1O3 perovskite

The magnetic and electrical properties in phase-separated La0.7Ca0.3Mn0.9Cu0.1O3 perovskite were studied in detail. Experimental results show that the substitution of Cu at Mn-site suppresses the ferromagnetic (FM) phase of La0.7Ca0.3MnO3 matrix and induces a charge ordering transition at ∼146 K. At ∼256 K, a Griffiths-like behaviour is observed. At low temperatures, the occurrence of an irreversible metamagnetic transition associated with a large relaxation rate is analyzed, clearly indicating the dynamic phase coexistence and evolution of FM islands. A magnetic phase diagram is finally constructed based on the magnetic measurements, summarizing the dynamic evolution process of phase separation.

Single crystal growth of Mn4Nb2O9 and its structure-magnetic coupling

A single crystal of Mn4Nb2O9 of about 8 mm in diameter and 30 mm in length was successfully grown by a newly designed one-step method based on the optical floating zone technique. Clear Laue spots and sharp XRD Bragg reflections attest the good crystal quality. The antiferromagnetic phase transition at TN = 108.4 K of the Mn4Nb2O9 single crystal was observed along the c axis, which contrasts with Co4Nb2O9 belonging to the same structural family. Structural changes with a-axis shrinkage and c-axis expansion at TN demonstrate a significant and anisotropic magnetostriction effect.