Exchange bias in a nanogranular system with competing ferromagnetic and antiferromagnetic exchange interactions
Exchange bias in a nanogranular system with competing ferromagnetic and antiferromagnetic exchange interactions
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DOI：
10.1002/pssb.201046430
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发表时间：
2011-12-01
影响因子：
1.6
通讯作者：
Du, An
中科院分区：
文献类型：
--
作者：
Hu, Yong;Du, An
采用改进的Monte Carlo大都会方法研究了具有反铁磁（FM）反铁磁（AFM）核基质形貌的纳米颗粒体系.的AFM和FM组件的比例上的交换偏置场（HE）和矫顽力（HC）的影响，分别在场冷却后，在低温。弱冷场（HFC）时HE符号为负，强冷场时HE符号为正。对于弱HFC和强HFC，随着AFM核半径（RAF）的增加，HE值单调增加，但FM矩阵的增加会使HE值减小;当HFC等于某一临界值时，HE值是非单调的，正好克服了AFM界面耦合能的影响。随着FM维数的增加，在弱或强HFC中冷却后，HE值均先减小，最后在低温处趋于稳定。然而，对于相同的临界HFC，HE约为零，并略微向正值偏移。HC的行为与HFC无关。在本系统中，HC随着RAF的增加而单调减小，而随着FM维数的增加而呈相反的趋势。通过对磁化反转和能量竞争机制的分析，对这一现象进行了解释。RAF的增加稳定了AFM纳米颗粒的磁自旋构型，有助于HE，而大量的FM自旋可能会削弱AFM钉扎效应，导致抑制HE。
A nanogranular system with inverted ferromagnetic (FM)antiferromagnetic (AFM) corematrix morphology is investigated by conducting a modified Monte Carlo Metropolis method. Effects of the AFM- and FM-component ratios on exchange bias field (HE) and coercivity (HC) are presented at low temperature after field cooling, respectively. The sign of HE is negative for weak cooling fields (HFC) but positive for strong ones. The value of HE increases monotonically with the increasing radius of the AFM core (RAF) at the expense of the FM matrix for weak and strong HFC, while it is non-monotonic when HFC is equal to a critical value, which just overcomes the AFM interfacial coupling energy. With the pure increase of the FM dimension, the value of HE decreases firstly and finally levels off at low temperature after cooling in weak or strong HFC. However, HE is around zero and shifts slightly to a positive value for the same critical HFC. The behaviors of HC are independent of HFC. A monotonic decrease of HC with increasing RAF and the opposite trend with increasing FM dimension are both detected in the present system. The phenomena have been interpreted well by analyzing the magnetization reversal and energy competition mechanisms. The increase of RAF stabilizes the magnetic spin configuration of the AFM nanoparticles to contribute to HE, while large numbers of the FM spins may weaken the AFM pinning effect, resulting in the suppression of HE.