金属离子掺杂对CuO基纳米复合材料的交换偏置调控

为了研究反铁磁基体中掺杂的金属离子对交换偏置效应的影响, 本文采用非均相沉淀法制备了纳米复合材料. X射线衍射图(XRD)和场发射扫描电子显微镜(SEM) 照片清晰表明CuO纳米复合样品具有统一的颗粒尺寸, 约为80 nm. 通过体系中掺杂磁性金属离子Ni和Fe, 实现了亚铁磁MFe₂O₄ (M=Cu, Ni)晶粒镶嵌在反铁磁(AFM) CuO 基体中. 在CuO基体中加入少量的Ni能改变两相交界面的磁无序从而生成类自旋玻璃相, 相应提高对铁磁相磁矩的钉扎作用. 同时, 场冷过程中反铁磁相内形成磁畴, 冻结在原始状态或磁场方向上, 畴壁也起到钉扎铁磁自旋的作用, 进而提高交换偏置效应. 随后加入的Ni 会生成各向异性能较大的NiO, 也能够提高交换偏置场. 在带场冷却下, 所有样品均发生垂直交换偏置, 也证明了样品在场冷过程中形成了自旋玻璃相, 正是由于亚铁磁与自旋玻璃相界面上的磁交换耦合, 才导致回线在整个测量范围内发生了向上偏移. 零场冷却和场冷却(ZFC/FC)情况下磁化强度与温度变化曲线(M-T)说明在这些复合材料中的交换偏置效应是由于存在亚铁磁颗粒和类自旋玻璃相界面处的交换耦合作用. 研究发现随着持续掺杂Ni离子, 交换偏置场先缓慢增加后又急剧增加, 生成各向异性能高的反铁磁相NiO 和反铁磁相内的畴态组织是这一结果的原因.

Exchange bias tuning of metal ions doped in CuO nanocomposites

In this paper, the nanocomposites are synthesized by the non-equal precipitation method to study the effect of the metal ions doped in antiferromagnetic matrix on the exchange bias. XRD patterns and SEM images reveal that the as-synthesized CuO nanocomposites have uniform size (～80 nm), and the ferrimagnetic particles MFe₂O₄ (M=Cu, Ni) are embedded in the antiferromagnetic (AFM) CuO matrix by doping of magnetic metal ions Ni and Fe. And the ferrimagnetic phase MFe₂O₄ (M=Cu, Ni) is formed through the addition of a small amount of Fe that reacts with Cu and Ni ions. Effects of different doping amount of Ni on exchange bias are different. A small doping amount of Ni can induce magnetic disorder at the interface of both phases, then the spin-glass-like phase may be formed. The spin-glass-like phases enhance the pinning effect on the magnetic moments of ferrimagnetic phase. Meanwhile, during field cooling process the antiferromagnetic phase splits into domains, which are aligned either with cooling field or in the original antiferromagnetic configuration. The domain wall serves as pinning sites for the magnetic moments of ferromagnetic phase, and the exchange bias effect is increased. The AFM NiO grains with high anisotropic energy are generated, this also increases the exchange bias effect when continuous doping of Ni ions. In the process of field cooling (FC), upward shift occurs in all hysteresis loops, which is perpendicular to the exchange bias. As x=0.08 (x is the concentration of Ni) the perpendicular displacement is 3.6%, this behavior also proves that under FC measurements, the spin-glass-like phase can be formed between the antiferromagnetic nanopaticles. It is the magnetic exchange coupling at the interface between the ferrimagnetic phase and the spin-glass-like phase that result in an upward shift in the entire measurement range. The plot of M versus T under zero field cooling (ZFC) and field cooling (FC) indicates that the exchange bias effect in these composites is ascribed to the exchange coupling at the interface between the ferrimagnetic particles and the spin-glass-like phase. With continuous introduction of magnetic Ni ions, the exchange bias field first increases slowly, then at x=0.08 it increases sharply. The existence of AFM NiO with high anisotropic energy and the domain structure in AFM matrix are the causes of the result.