Papers by Keyword: Exchange Bias

Abstract: Ferromagnetic (FM) FeCo is investigated in exchange bias systems. The ferromagnetic layer is grown on a FeMn antiferromagnetic (AFM) layer. Partial superficial oxidation of FeCo is observed. The standard field cooling procedure results in a large room temperature exchange bias effect. However, the training effect observed when the hysteresis loops are repeated does not have a saturating trend. This behavior is related to the evolution of pinned moments at the FM/AFM interface. X-ray circular magnetic dichroism technique is used to clarify this mechanism.

Abstract: This paper presents an investigation of the exchange bias of the Fe/Fe₃O₄ layer deposited on the Ag/hollow glass microspheres. The results show that exchange bias is affected by different thickness of Fe₃O₄ layer which is caused by different reaction time. The exchange bias field (H_E) increases gradually with increasing reaction time, and achieves maximum value when the reaction time reaches 30min; after that, it decreases. It is also found that the changes of exchange bias field (H_E) are proposed to the frozen interfacial spins and the structural lattice disorder

Abstract: Samples of Ca_yFe_12-yO₁₉ (0 ≤ y ≤ 1.0) were prepared by a proteic sol–gel process with hematite phase and clusters of M-type calcium hexaferrite. Impedance analysis showed that the resistivity increased with calcium concentration in the 0.0 < y ≤ 0.2 range, but decreased for y > 0.2. The saturation of the electrical resistivity occurred at 7.5 × 10⁶ Ω·cm for Ca_0.9Fe_11.1O₁₉. The plot of magnetization as a function of the magnetic field showed high values of saturation magnetization (40 emu/g) with low remanence (6.7 emu/g) and coercive field (320 Oe).

Abstract: Novel methods of switching magnetism with electric fields and vice versa, and aiming at magnetoelectric (ME) data processing are reported. First, the patented MERAM^@ uses the electric field control of exchange bias via an epitaxial Cr₂O₃ layer and exchange coupling to a Pt/Co/Pt trilayer. It promises to crucially reduce Joule energy losses in RAM devices. Second, magnetic switching of the electric polarization by a transverse magnetic field in a 3-1 composite of a vertically poled BaTiO₃ thick film embedding CoFe₂O₄ nanopillars produces a regular surface polarization pattern with rectangular symmetry. Its possible use for data processing is discussed.

Abstract: Magnetic spin valve structures have a great practical interest as sensors of magnetic fields, hard disk read heads and elements of magnetic random access memories (MRAM). Despite the large number of experimental and theoretical work on spin valve structures, the effects of interlayer interactions occurring in these structures, at present time are not fully understood. Introduction

Abstract: We report the exchange bias properties in the bulk Ni₄₅Co₅Mn₃₈Sn₁₂ quaternary Heusler alloy. The ferromagnetic (FM) –antiferromagnetic (AFM) interactions get reinforced after the Co substitution for Ni in the Ni-Mn-Sn alloy, which increase the exchange bias field (HE). A maximum shift in hysteresis loops of 306 Oe was observed in the 10 kOe field cooled sample. The origin of this large exchange bias field has been discussed. Magnetic hysteresis loop obtained in the zero field cooled (ZFC) mode shows double-shifted loop, and the reason of this phenomenon has been explained in detail.

Abstract: The (Co₂MnSi)_1-x-(NiO)_x (x = 0.0, 0.1, 0.2, 0.3) nanocomposites were fabricated by mechanical alloying using Co₂MnSi Heusler alloy and NiO nanoparticles. It is revealed that antiferromagnetic NiO nanocrystallines dramatically enhances the magnetoresistance of the nanocomposites more than 20 times larger than that of the NiO-free Co₂MnSi alloys at 300 K. The Exchange bias effect of the nanocomposites suggests that the spin-dependent tunneling and scattering at the interfaces of ferromagnetic/antiferromagnetic are responsible for the enhancement of the magnetoresistance.

Abstract: The influnence of the amplitude (H0) and frequency of sweeped magnetic field on the exchange bias He and coercivity Hc for ferromagnetic/ antiferromagnetic films has been simulated with Monte Carlo method. In a cycle, the sweeped frequency is inversely proportional to Monte Carlo steps (MCSs). It is observed that, for smaller MCSs, the values of He and the blocking tempreture Tb reduce evidently with increasing MCSs; for larger MCSs, the values of He and Tb decrease gently with increasing MCSs. It is also found the values of He and Tb decrease obviously with increasing values of H0 (HN0). However, on the contrary, the value of Hc increases with increasing values of H0 (HN0). At low temperature and little HN0, the asymmetric loop may appear, which is attributed to the competition between the relaxation time and the period of the external magnetic field. Moreover, the symmetry of the loops influences evidently the values of He and Hc.

Abstract: We have used ferromagnet/antiferromagnet/ferromagnet sandwich structure to probe the antiferromagnetic layer thickness dependence of exchange bias in sputter-deposited Co/CoO/Co trilayer. The exchange coupling occurring at the upper ferromagnetic/antiferromagnetic interface is always found to be stronger than the one at the lower antiferromagnetic/ferromagnetic interface. The grain growth with increasing antiferromagnetic layer thickness can lead to a gradient of grain size distribution through the whole antiferromagnetic layer. Consequently, the relatively large grains at the upper interface would results in a rougher interface which we treat as structural defects and can significantly enhance exchange bias through domain state model. The slightly decrease of exchange coupling with increasing antiferromgnetic layer thickness indicates that the exchange bias is only governed by the grains that are thermally stable but whose anisotropy energy is low enough to be set.

Abstract: We have investigated the relationships between the electric field-induced resistance change and the strength of the exchange interaction of the Cr2O3/ La0.7Sr0.3MnO3 (LSMO) magnetic hetero system. The hetero system subjected to field cooling (FC) showed a positive shift in the magnetization curves due to an exchange bias. The exchange bias field changed depending on the FC field. Resulting from the exchange behaviors, the resistance of LSMO film was changed by the application of an electric field to the Cr2O3 gate. This resistance change is more likely due to the interface interaction strength between the Cr2O3 and LSMO film