Liang Xie

Reversal of spontaneous magnetization and spontaneous exchange bias for Sm1−xYxCrO3: The effect of Y doping

We report the crystal and electronic structures and magnetic properties of non-magnetic Y3+ ion doped SmCrO3 crystals. Structural distortion and electronic structure variation are caused by cation disorder due to Y doping. Although the spin moment of Sm3+ is diluted by nonmagnetic Y ions, spin reorientation continues to exist, and the temperature-dependent magnetization reversal effect and the spontaneous exchange bias effect under zero field cooling are simultaneously induced below Neel temperature. Significantly, the method of doping promotes the achievement of temperature dependent tunable switching of magnetization and sign of a spontaneous exchange bias from positive to negative. Our work provides more tunable ways to the sign reversal of magnetization and exchange bias, which have potential application in designing magnetic random access memory devices, thermomagnetic switches and spin-valve devices.

The tunable spin reorientation, temperature induced magnetization reversal, and spontaneous exchange bias effect of Sm0.7Y0.3Cr1−xGaxO3

In this work, we investigated the temperature dependent magnetic properties of SmCrO3 by codoping nonmagnetic ions at Sm- and Cr-sites. The spin reorientation from Γ4 to Γ2 is tuned and the transition temperature TSR is improved dramatically to near the liquid nitrogen temperature by Ga ion doping, which would be helpful to achieve its application in temperature sensitive spintronic devices and magnetic switching devices. An intrinsic temperature induced magnetization reversal effect from positive to negative under zero-field-cooling conditions is induced as well and its reversal evolution is strongly dependent upon doping. Moreover, the zero-field-cooling exchange bias effect still exists and shows a positive exchange bias field although it is suppressed with increase of doping concentration. Under the influence of doping nonmagnetic ions, lattice distortion is induced to some extent and the magnetic interactions of Cr–Cr and Sm–Cr are predominantly diluted, realizing control of the above phenomena. Those phenomena are discussed and successfully explained by considering the magnetic exchange interaction competitions including the isotropic, antisymmetric (or Dzyaloshinskii–Moriya interaction), and anisotropic superexchange interactions.

Lattice Structure and Magnetic Behavior of Ga Ion Doped Multiferroics CaMn7O12

The lattice structure and magnetism of polycrystalline CaMn7-xGaxO12 (x = 0, 0.1, 0.2, 0.3, 0.4) synthesized by solid state method have been investigated. The refined x-ray diffraction patterns show that a well single phase Ga doped CaMn7O12 crystals can be obtained by solid state method and their lattice structure is rhombohedral with R-3. The lattice parameter a linearly decreases while parameter c linearly increases with increasing doping concentration, leading to a lattice distortion. Magnetic susceptibility and inverse susceptibility as a function of temperature show that CaMn7-xGaxO12 and undoped CaMn7O12 behave the basically identical magnetic characterization, that is, there are two magnetic phase transitions at 90 K and 40 K. And the antiferromagnetic transitional temperature is not obviously influenced by non-magnetic Ga ions doping. However, the magnetization at temperature lower than 40 K is enhanced and there is a new transitional temperature point observed at temperature range between 40 and 90 K, which indicates that Ga ions participate into the magnetic interaction.

The structural and magnetic investigation of (x) BiFe0.95Co0.05O3: (1-x) La0.7Ca0.3MnO3 composites

The structural and magnetic behaviors are studied in the composites (x) BiFe0.95Co0.05O3: (1-x) La0.7Ca0.3MnO3. An influence on the lattice parameters and magnetic states of BiFe0.95Co0.05O3 (BFCO) to the La0.7Ca0.3MnO3 (LCMO) are investigated. Although the variation of the relative X-ray intensity of LCMO to BFCO with composition (x) in XRD patterns and the randomly distributed small nanoparticle of LCMO (~200xa0nm) mixed in the large nanoparticle of BFCO (~900xa0nm) given by SEM images indicate an almost immiscibility of BFCO and LCMO in composites obtained by solid solution method, an obvious change of lattice parameters indicates their mutual influence on lattice structure. A detail magnetic investigation of the composites shows that the Griffiths phase is increased with increase of composition x due to the incorporation of ferromagnetism of BFCO to the paramagnetic phase of LCMO. An approximate magnetic phase diagram for the composites is established, which would be helpful for understanding the magnetic singularity of the composites with colossal magnetoresistance and multiferroics.

Pb- and Sm-doping effects on the vortex dynamics in Bi4O4S3 superconductor

Polycrystalline samples of Bi4O4S3, Bi3.94Pb0.06O4S3, and Bi3.94Sm0.06O4S3 were synthesized using a conventional solid-state reaction method. The vortex dynamics of these samples are studied and compared through measuring the critical current density (Jc) and magnetic relaxation. The estimated Jc value of three samples at temperature 2u2009K decreases with doping Pb and Sm elements due to the depression of the superconductivity. The normalized pinning force response with reduced field follows the Kramer scaling law f(h)∝u200ahp(1−h)q, and the maximum of the reduced field (hmax) is observed at 0.31, 0.24, and 0.18 for Bi4O4S3, Bi3.94Pb0.06O4S3, and Bi3.94Sm0.06O4S3, respectively, indicating the presence of both surface and point pinning centers in these samples. The barrier energy estimated by the magnetic relaxation data depends on the field as a negative power law U0∝Hn and the magnetic relaxation rate S exhibits a considerable monotonic increase with magnetic field, which corroborates a plastic nature of the cr...

Effect of Annealing on Room Temperature Multiferroics of BiFe1-xCoxO3

We studied the effect of annealing and Co ion doping on the structure, leakage current, ferroelectric polarization and magnetism of BiFeO3 samples. X-ray diffraction patterns demonstrate that an appropriate Co doping concentration is favor of suppressing the secondary phase but annealing treatment is apt to the growth of both the main and the secondary phases. The current density as a function of an electric field indicates that Co doping increases the leakage current density as samples before annealing but suppresses it after annealing. Annealing treatment improves the leakage for Co-doped sample and reduces it for the undoped sample. Ferroelectric hysteresis loops reflect that Co ions doping is liable to increase the ferroelectric polarization, while the sample is annealed it will do opposite effect. However the annealing treatment do improve the ferroelectricity for pure BiFeO3 sample. The magnetic hysteresis at room temperature shows the obvious enhancement of ferromagnetic properties with the sample after annealing.

Annealing temperature dependence of local atomic and electronic structure of polycrystalline La0.5Sr0.5MnO3

The local atomic and electronic structure of La0.5Sr0.5MnO3 was investigated at different annealing temperatures (TA) by X-ray absorption spectroscopy (XAS) and photoemission spectroscopy (XPS). The extended X-ray absorption fine structure indicates that the MnO6 octahedral distortion is reduced by increasing TA. The chemical shift for the sample with TA = 1350°C measured by XPS of Mn 2p core level demonstrates the increasing of Mn3+ ions content. From the deconvolution of valence band photoemission spectra, the number of eg electron is also proved to increase with increasing TA. It is also demonstrated that there is a strongest hybridization between O 2p and surrounding atomic orbital states in sample with TA = 1350°C, which is consistent with valence band photoemission.