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The crystal structure and magnetic properties of hexagonal YMn0.9Cu0.1O3 single crystal are systematically investigated. The refinement results of XRD show the lattice constant decreases, which is unusually due to the doped Cu2+ ion has a larger ionic radius than the Mn3+ ions. The XPS results show that the coexistence of Mn2+, Mn3+ and Mn4+ ions in YMn0.9Cu0.1O3 single crystal. Magnetization measurements show that Cu doped YMn0.9Cu0.1O3 and parent YMnO3 have almost the same antiferromagnetic transition temperature TN, which indicates the AFM interaction is robust in the geometry frustrated system. Because doping directly destroy some of the Mn3+ ions nets, the relaxation of frustration of Mn in-plane 2D triangular geometry network leads to the significantly decrease of Mn3+ ions AFM interaction. In addition, the coexistence and competition between the ferromagnetic and antiferromagnetic interactions among the Mn2+, Mn3+ and Mn4+ ions lead to a complicated and irreversible magnetization behavior in YMn0.9Cu0.1O3 single crystal.

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 polycrystalline ceramics of Y 1− x Ho x Fe 0.5 Cr 0.5 O 3 (x = 0, 0.05 and 0.1) are synthesized by a sol-gel method. The magnetization reversal and exchange bias effect are investigated in single phase bulk Y 1− x Ho x Fe 0.5 Cr 0.5 O 3 . Magnetic Ho 3+ ion as a dopant is introduced into the system to confirm the influence of A-site ion on the magnetic interactions. The dual reversal of exchange bias field for x = 0.05 is observed, and its characteristic temperatures are corresponding to the compensation temperatures of magnetization reversal. The exchange bias field of x = 0.1 is found to be ∼10.03 kOe at 4 K, revealing a large value compared with that of x = 0. A schematic diagram based on the competition between the single ion anisotropy and Dzyaloshinsky-Moriya interaction, and the antiparallel coupling between the Ho 3+ moments and the canted Cr 3+ /Fe 3+ moments, is used to understand the dual reversal phenomenon of magnetization and exchange bias effect.

The effects of Cr3+ ions doping on the magnetic and magnetocaloric properties of manganites La0.5Sr0.5Mn1−xCrxO3 (x=0.05, 0.1, 0.15, and 0.2) have been investigated. The magnetization measurements show that a ferromagnetic cluster behavior is induced by Cr3+ dopants and the paramagnetic to ferromagnetic transition temperature TC decreases from 319 to 251 K with increasing Cr3+ content from 0.05 to 0.2. The positive slope of the Arrott plots near TC indicates a second order phase transition. The magnetic entropy change (−ΔSM) is estimated from the isothermal magnetization measurements, and the maximum of the magnetic entropy change (−ΔSmaxM) near TC shows a power law dependence of magnetic field: −ΔSmaxM = m ( μ 0 H ) n with n being close to the predicted value ~2/3. The experimental results suggest that the magnetic entropy change and TC can be tuned by changing the Cr3+ ions doping level, which offers an effective method for finding an optimal doping level for magnetic refrigeration near room temperature.

Pulsed high magnetic fields up to 52 T have been used in the systematic investigation of the magnetic properties of manganites Nd 0.5 Sr 0.5 Mn 1− x Cu x O 3 (0≤ x ≤0.15). The Cu-doping dependent first-order metamagnetic transitions are observed below the charge ordering temperature, which is ascribed to both Cu-doping and field-induced collapse of the charge ordering with antiferromagnetic phase. Based on the magnetization and electrical transport measurements, a three-dimensional phase diagram with coordinate axis of temperature, magnetic field, and doping level has been obtained, in which the critical fields of the metamagnetic transitions increase with the increase in Cu content and decrease with increasing temperature. The experimental results confirm that Mn-site substitution with Cu destroys the Mn 3+ –O 2− –Mn 4+ bridges and weakens the double exchange interaction between Mn 3+ and Mn 4+ ions, which shows an obvious tuning effect on the metamagnetic transition under the external magnetic field.

Polycrystalline Sm3Fe5O12 ceramics are synthesized by a sol–gel method. High temperature dielectric properties in the frequency range from 100 Hz to 10 MHz are investigated at different temperatures from 300 to 800 K. This material exhibits high dielectric permittivity and low dielectric loss in a wide range of temperature and frequency. The contribution of electrode polarization to the dielectric permittivity is ruled out by the dc bias voltage measurement at room temperature. Two types of dielectric relaxations are clearly observed, and both of them are thermal activated relaxations following the Arrhenius law. The high frequency relaxation is shown to originate from the carrier hopping between Fe2+ and Fe3+, while the low frequency relaxation most likely arises from the conduction. The concentration of Fe2+ is proved to influence the low frequency dielectric relaxation.

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 zero-field cooled exchange bias (ZEB) and conventional field cooled exchange bias (CEB) effects are investigated in single phase bulk SmCrO 3 ceramics below the spin reorientation transition temperature. The ZEB field is found to be ~5.065 kOe at 20 K, revealing a large value compared with other ZEB systems. Nonmagnetic La 3+ as a dopant is introduced into the system to confirm the influence of Sm 3+ on the ZEB effect. A schematic diagram based on the coupling between the internal magnetic sublattices of Sm 3+ and Cr 3+ is used to understand the ZEB effect.

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.

In this study we report detailed magnetic property of the 4f-3d pseudo-quaternary Tb0.2Pr0.8(Fe0.4Co0.6)1.88C0.05 compound by detailed magnetization measurements. Very sharp magnetization jumps across the antiferromagnetic–ferromagnetic transition are observed below 3.0 K, and the number of jump-like transitions increases with decreasing temperature. The time-dependent magnetic relaxation, field sweep rate and cooling field dependence of magnetization jumps resemble the martensitic scenario. The number and occurrence of magnetization jumps are mainly determined by the competitions between the thermal fluctuation energy, elastic energy and Zeeman energy, and the field-induced antiferromagnetic to ferromagnetic phase transition at low temperatures is of first-order in nature.

Structural, magnetic, and electric properties have been investigated in polycrystalline Bi{sub 2}(Fe{sub 1−x}Al{sub x}){sub 4}O{sub 9} (0≤x≤0.25) ceramics synthesized by a modified Pechini method. Structural analysis reveals that Al{sup 3+} doped Bi{sub 2}Fe{sub 4}O{sub 9} crystallizes in orthorhombic structure with Pbnm space group. Surface morphology of the end products is examined by scanning electron microscopy and the grain size has a tendency to decrease with increase in Al{sup 3+} doping level. Compared with pure Bi{sub 2}Fe{sub 4}O{sub 9}, room temperature coexistent multiferroic-like behavior is observed in Al{sup 3+} doped Bi{sub 2}Fe{sub 4}O{sub 9}. By analyzing magnetic properties, the Neel temperature monotonously shifts to low temperatures from ~260 K (x=0) to ~35 K (x=0.25). Moreover, the spin dynamic measured by the shift in ac magnetic susceptibility as a function of frequency provides a possibility of spin-glass-like behavior, which is further confirmed by fitting the critical slowing down power law and memory effect. - Graphical abstract: Compared with pure Bi{sub 2}Fe{sub 4}O{sub 9}, room temperature weak ferromagnetic property and enhanced ferroelectric-like behavior can be achieved simultaneously with proper Al{sup 3+} doping. - Highlights: • Bi{sub 2}(Fe{sub 1−x}Al{sub x}){sub 4}O{sub 9} (0≤x≤0.25) ceramics are fabricated via a Pechini method. • Weak ferromagnetic andmore » ferroelectric behaviors can be achieved simultaneously. • Spin-glass-like behavior is detected with proper Al{sup 3+} doping. • The memory and aging effects are observed with proper Al{sup 3+} doping.« less

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.

The structure and magnetic properties of non-magnetic Ga 3+ ion doped CuFe 1− x Ga x O 2 ( x =0, 0.03, and 0.05) single crystal samples were investigated. X-ray diffraction patterns analysis confirms that the samples are single-phase crystallizing. Doping effect on the magnetic behavior of the ground state and the field-induced spin flip/flop transitions were detected. The transition temperatures and critical magnetic fields of the spin flip/flop, as well as the magnetic hysteresis directly depend on the Ga 3+ doping level. Such doping effects may associate with the competition between dilution effect (partial release of spin frustration) and the induced local magnetic moment, which is the result of the changed magnetic coupling both inter- and intra-planes of Fe ions. Based on the experimental results, the effects of Ga 3+ doping on the spin flip/flop behavior and a detailed high field magnetic diagram were assumed.

Electrical transport and magnetic properties of La0.5Sr0.5Mn1−xTixO3 (x = 0, 0.1, 0.15 and 0.2) have been investigated. Experimental results show that the different Ti4+ doping level has obviously different effect on electrical transport and magnetization properties. Especially, a martensitic transition was observed in higher Ti4+ doping levels (x = 0.15, 0.2). In which a doped Ti4+ ion substitutes a Mn4+ ion, with increasing in Ti4+ doping level from x = 0 to 0.2, the ratio of Mn3+/Mn4+ increases from 1 to 5/3, that is the coupling via Mn3+–O2−–Mn4+ double exchange increases leading to a localized ferromagnetic domain in the charge ordering of matrix of La0.5Sr0.5MnO3. With the increasing of magnetic field to a critical field, the localized magnetic moment was delocalized and rotated to parallel to an applied field showing a martensitic transition.

Magnetizations of the Fe doped Sr 3 Cr 2 O 8 single crystals Sr 3 Cr 2− x Fe x O 8 ( x =0, 0.05 and 0.1) were investigated in the temperature ranging from 2 to 300 K and the magnetic field ranging from 0 to 16 T. Based on the Curie–Weiss law and the Bleaney–Bowers model, the low field magnetization behaviors were analyzed. Experimental results show that the Fe 5+ dopant has influence on the intradimer interaction J 0 , the interdimer interaction J' , and the average change rate Δ χ / Δ T of spin-dimer susceptibility χ d i m e r of Sr 3 Cr 2− x Fe x O 8 . Especially, in this spin-dimer system, the Fe 5+ dopant can obviously enhance the magnetic sensitivity of singlet to triplet transition in Sr 3 Cr 2 O 8 .

A drought-induced gene, DIP3, encoding a chitinase III protein was isolated from the roots of upland rice by reverse transcription-polymerase chain reaction (RT-PCR). Sequence analysis demonstrated that the cDNA and deduced protein showed high identity to Oryza sativa class III chitinase. The deduced protein contained a signal peptide sequence in the N-terminal region of 21aa and a conserved glycosyl hydrolase (GH) 18 domain. The secondary and 3D structures were analyzed and showed that it contained α-helix, β-sheets, extended strand and random coil structures and that it was approximately spheroidal. Real-time quantitative PCR analysis revealed that expression levels accumulated rapidly under different forms of abiotic stress (drought, salt and low temperature), peaked at different times and then decreased. These results implied that as a member of class III chitinases, DIP3 may function as a stress-induced protein involved in the regulation of plant stress response.

The exchange bias (EB) effect is observed in Bi2Fe3AlO9 polycrystalline ceramics. The EB field (HEB), vertical magnetization shift, and coercive field show a strong dependence on the cooling fields. When a larger applied field is used to measure the hysteresis loop, the EB effect is suppressed. The induced spin-glass-like phase via Al3+ doping is responsible for the EB effect below the spin-glass temperature (TSG) of ∼25 K. Moreover, the HEB varies nonmonotonically with temperature above TSG, which is interpreted using a random field model with the exchange coupling between ferromagnetic clusters and an antiferromagnetic phase.