Exchange bias in magnetic nanoparticle capped with amorphous magnetic shell
Exchange bias in magnetic nanoparticle capped with amorphous magnetic shell
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DOI：
10.1063/1.3624751
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发表时间：
2011-08
影响因子：
3.2
通讯作者：
Ha M. Nguyen;Chih‐Hao Lee;P. Hsiao;M. Phan
中科院分区：
文献类型：
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作者：
Ha M. Nguyen;Chih‐Hao Lee;P. Hsiao;M. Phan
采用扩展的蒙特卡罗(MC)模拟方法研究了由铁磁(FM)核和非晶磁(AM)壳组成的纳米颗粒的交换偏置。由随机磁各向异性(RMA)控制的AM壳层的磁性玻璃有序是导致FM磁芯单向各向异性的原因。我们的MC结果表明，虽然偏置场和矫直力与RMA强度有很强的依赖关系，类似于传统FM/AFM双层膜中的反铁磁(AFM)厚度，但它们与AM厚度无关。然而，偏置场和矫直力随着磁芯尺寸的增大而急剧变化，当磁芯尺寸足够大时，偏置磁场和矫顽力会趋于饱和。冷却场和温度依赖关系显示出偏置场的奇特符号反转。我们的研究支持这一观点，即在某些磁性纳米颗粒或纳米晶合金中观察到的交换偏置不一定是由于AFM相的存在。
An extensive Monte Carlo (MC) simulation is performed to investigate exchange bias in a novel model of a nanoparticle consisting of a ferromagnetic (FM) core and an amorphous magnetic (AM) shell. The magnetic glassy ordering of the AM shell governed by random magnetic anisotropy (RMA) is shown to be responsible for the unidirectional anisotropy to the FM core. Our MC results show that, while the bias field and coercivity exhibit a strong dependence on RMA strength, which looks like that on the antiferromagnetic (AFM) thickness in traditional FM/AFM bilayers, they are independent of AM thickness. However, the bias field and coercivity abruptly change with increasing small core size and get saturated for a large enough core size. The cooling field and temperature dependencies show the peculiar sign inversion of the bias field. Our study supports the argument that the exchange bias observed in some magnetic nanoparticles or nanocrystallined alloys is not necessarily due to the presence of an AFM phase.