Papers by Keyword: Antiferromagnetic

Abstract: The study of the perovskite manganites La_0.47Ca_0.53Mn_1-xCu_xO₃ with x = 0, 0.06, 0.09, and 0.13 has been done. The magnetic structure was determined using high-resolution neutron scattering at room temperature and low temperature. All samples were paramagnetic at room temperature and antiferromagnetic at low temperature. Using the SQUID Quantum Design, the samples showed that the doping of the insulating antiferromagnetic phase La_0.47Ca_0.53MnO₃ with Cu doping resulted in the temperature transition from an insulator to metal state, and an antiferromagnetic to paramagnetic phase. The temperature transition from an insulator to metal state ranged from 23 to 100 K and from 200 to 230 K for the transition from an antiferromagnetic to paramagnetic phase.

Abstract: The giant magnetoresistance (GMR) effect in FeMn/NiCoFe/Cu/NiCoFe spin valve prepared by dc opposed target magnetron sputtering is reported. The spin valve thin films are characterized by Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometer (VSM) and magnetoresistance ratio measurements. All measurements are performed in room temperature. The inserted 45 mm thickness FeMn layer to the NiCoFe/Cu/NiCoFe system can increase the GMR ratio up to 32.5%. The coercive field to be increased is compared with different FeMn layer thickness. Furthermore, the coercive field (Hc) decreases with increasing FeMn layer thickness. Magnitude of coercive field is 0.1 T, 0.09 T and 0.08 T for FeMn layer thickness is 30 nm, 45 nm and 60 nm, respectively. The FeMn layer is used to lock the magnetization in the ferromagnetic layer through the exchange anisotropy. This paper will describe the development of a GMR spin valve and its magnetic properties.

Abstract: Within the frame of average spin model the calculation of dependence of critical phase transition temperature in antiferromagnetic ultrathin films of different crystalline structure on their thickness has been carried out. I has been shown, that relative change of Neel temperature is subject to power law with exponent close to the experimental values.

Abstract: We report on possible types of spatially modulated antiferromagnetic structures in the biaxial multiferroic and their stability depending on the ratio of the magnetic anisotropy and flexomagnetoelectric interaction parameters.

Abstract: We have performed detailed structural, electronic and magnetic properties of high - TC multiferroic CuO using first principles density functional theory. The total energy results revealed that AFM is the most stable magnetic ground state of CuO. The DOS and electronic band structure calculations show that in the absence of on-site Coulomb interaction (U), AFM structure of CuO heads to a metallic state. However, upon incorporating U in the calculations, a band gap of 1.2 eV is recovered. Furthermore, the Born effective charges calculated on Cu does not show any anomalous character.This suggests that the polarization seen in CuO could be attributed to the spin induced AFM ordering effect.

Abstract: Sr-doped LaTiO₃ (SLTO) thin epitaxial films on LaAlO₃ (100) have been fabricated by the off-axis rf magnetron co-sputtering system. The dopant Sr²⁺ ions were expected substituting La³⁺ ions in the films to introduce the hole carriers. The X-ray diffraction shows that the [001] direction of the SLTO films is perpendicular to the substrate surface. The in-situ grown specimens were measured the temperature dependence of resistivity and the Hall coefficients to study the transport properties. The Hall measurements show that the carrier is electron for Sr-doping over 16%. The temperature dependence of the resistance shows that the n-type films are metallic and deviate from free electron gas model obviously. We found the behaviour could be well described by the small-polaron coherent motion model.

Abstract: The solid solutions of NdFeO₃-Bi₂SrNb₂O9 (1:1ratio) of the Aurivillius-type compounds was prepared by solid-state reaction. The room structural data were obtained from X-ray diffraction (XRD) and confirmed a Three-layered Aurivillius phase. The dielectric measurement showed no anomalies due to the high conductivity of these samples at elevated temperature. From the magnetic measurement the compounds were found to be of canted antiferromagnetic at room temperature. It is revealed that the formation of Fe²⁺ can be suppressed by the pre-oxidation of Fe₂O₃，This result may have implications for further studies on leakage current control of these materials. In all, we’ve synthesized a new material that is ferroelectromagnetic in nature.

Abstract: Specially picked up web-chamber is used for visualization of domain structure in hematite. An analysis of domain configuration shows, that domain structure of hematite in a basal plane represents multilayered structure which contains domains both in paralleled thickness and in the parallel basal planes. The temperature features of magnetic permeability and domain structures in Fe2O3:Ga crystals near the Morin transition are investigated. Observable changes of magnetic permeability and changes in domain structure confirm that transition from АFM to WFM occurs in the hematite with Ga impurity as transition of the first sort. Results of research of antiferromagnetic and weakly ferromagnetic resonances (AFMR and WFMR) in these compounds are presented.

Abstract: Ordered perovskite-type oxides, Ca2MTeO6 (M = Mn, Co, Mg), were synthesized by a solid-state reaction method. All of samples belonged to space group P21/n and were insulators at room temperature. However, their electronic conductivities tended large gradually with a rise of temperature. Ca2MnTeO6 and Ca2CoTeO6 showed anti-ferromagnetism, and their Neel temperatures were 10 K and 7 K, respectively. The effective magnetic moment of manganese ion was 5.8 μB while its valence was bivalence in Ca2MnTeO6.