Search

The Dy3+ doped SmCrO3 polycrystalline ceramics are prepared by solid state method. The structure and magnetic properties are investigated. All samples show orthorhombic structure with space group Pnma. Three magnetic transitions are detected in Dy3+ doped SmCrO3 samples, which arise from the Cr3+-Cr3+ interactions and the spin reorientation of Cr3+, respectively. Both field cooled (FC) and zero field cooled (ZFC) exchange bias (EB) effects are observed in the prepared Sm1-xDyxCrO3 (x = 0 − 0.5) samples below the spin reorientation temperature (TSR), and the EB field (HEB) increases dramatically below TSR. With the increase of the doping level, the HEB is depressed. Three anomalous variations of magnetic entropy change (ΔSM) derived from the isothermal magnetization are observed, which are consistent with the magnetic transitions. Compared with the ΔSM after ZFC processes, the anomalous variations of ΔSM at ~25 K almost disappear after FC processes due to the enhanced unidirectional anisotropy, and no obvious influence is observed for the other two anomalous variations after FC processes.

The structural, magnetic, and dielectric properties of the Y1−xHoxFe0.5Cr0.5O3 (x=0, 0.05, 0.1, 0.3, and 0.5) compounds have been investigated. Rietveld refinement of the XRD patterns shows that the compounds possess orthorhombic perovskite structure. The dual magnetization reversal is observed in the samples with x=0.05 and 0.1, and it vanishes when x≥0.3. Ferromagnetic-like behavior with large coercive fields is observed in all Ho3+ doped YFe0.5Cr0.5O3 samples, indicating a doping induced metamagnetic behavior. This abnormal magnetization behavior can be explained by the antiparallel magnetic coupling between the Ho3+ and the canted Cr3+/Fe3+ moments, as well as the Ho–O–Ho magnetic interaction. The dielectric behavior in the frequency range from 100 Hz to 10 MHz is investigated. The low doped samples (x=0, 0.05, and 0.1) exhibit relaxation-like dielectric behavior and colossal dielectric constant in a wide temperature and frequency range. The dual magnetization reversal under low magnetic field makes these materials attractive candidates for the magnetic dual sensor devices.

The crystal structure and magnetic properties of hexagonal Y 0.95 Eu 0.05 MnO 3 single crystal were systematically investigated. The refinement structure analysis of Y 0.95 Eu 0.05 MnO 3 using single crystal XRD shows that Eu doping results in an expansion of the MnO 5 bipyramids along the c axis, and the contraction of the Mn forming trimerization in the ab plane. Magnetization measurements show that Eu dopant leads to the magnetic anisotropy change. Meanwhile, a spin glass behavior and a large zero-field cooled (ZFC) exchange bias (EB) effect of 735 Oe are observed due to the Eu doping. Based on the results, we proposed that (1): the spin glass phase of Y 0.95 Eu 0.05 MnO 3 mainly results from the intrinsic magnetic frustration and the disorder coming from Eu dopant; (2) the coupling between ferromagnetic spin glass phase and the frustrated antiferromagnetic phase leads to the exchange bias effect.

The temperature-induced dual magnetization reversal and field-induced spin reorientation transition are observed in Y 0.95 Ho 0.05 Fe 0.5 Cr 0.5 O 3 . The Ho 3+ dopant improves the sensitivity of the magnetization switching and weak ferromagnetism of YFe 0.5 Cr 0.5 O 3 . Based on the experimental results, we suggest that the ferrimagnetic ground state and the magnetization reversal mainly result from the antiferromagnetic coupling of weak ferromagnetic moments of Fe–O–Fe and Cr–O–Cr with that of Fe–O–Cr and Ho–O–Fe/Cr interactions. The fact that the magnetization reversal of Y 0.95 Ho 0.05 Fe 0.5 Cr 0.5 O 3 under a lower magnetic field makes it attractive candidates for the magnetic dual sensor devices.

The magnetization behavior of Ti 4+ doped perovskite manganites La 0.5 Sr 0.5 Mn 1− x Ti x O 3 ( x =0.15, 0.175 and 0.2) was investigated. Experimental results show that Ti 4+ dopant suppresses the antiferromagnetic charge ordering and leads to a step-like magnetization behavior below 3 K. The step-like transitions and the critical magnetic fields are strongly dependent on the Ti doping level, magnetic field sweep rate and temperature. Above 3 K, the step-like transitions transform to broad ones. In addition, under pulsed high magnetic fields with an ultrafast field sweep rate of ~10 3 T/s, the sharp step-like transitions observed in the static magnetization measurements become smooth metamagnetic transition at low temperatures. This feature is correlated with the collapse of the balance between the magnetic energy and elastic energy in the phase separation system within a martensitic-like scenario.

Polycrystalline RFeO 3 (R=La, Pr, and Sm) ceramics have been synthesized by a modified Pechini method. All the refined X-ray diffraction patterns reveal that the materials crystallized in orthorhombic structure with space group Pbnm . Clear grain and grain boundary are evident in PrFeO 3 and SmFeO 3 ceramics after sintering at 1200 °C for 4 h by scanning electron microscopy. Mixed valence of Fe 2+ /Fe 3+ has been determined using X-ray photoelectron spectroscopy. High-temperature dielectric behavior and impedance spectrum over the frequency range of 100 Hz to 10 MHz are investigated at different temperatures from 300 to 600 K. These materials exhibit relaxation-like dielectric behavior and colossal dielectric constant in a wide temperature and frequency range. Impedance spectrum analysis indicates the ceramics to be electrically heterogeneous consisting of semiconducting grains and insulating grain boundaries (corresponding to high and low frequency electrical response, respectively), which played important roles in the high-temperature dielectric properties of RFeO 3 ceramics.