Exchange bias in Co/CoO core-shell nanowires: Role of antiferromagnetic superparamagnetic fluctuations
Exchange bias in Co/CoO core-shell nanowires: Role of antiferromagnetic superparamagnetic fluctuations
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DOI：
10.1103/physrevb.80.064427
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发表时间：
2009-05
影响因子：
3.7
通讯作者：
T. Maurer;F. Zighem;F. Ott;G. Chaboussant;G. André;Y. Soumare;J. Piquemal;G. Viau;C. Gatel-C.-Gate
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文献类型：
--
作者：
T. Maurer;F. Zighem;F. Ott;G. Chaboussant;G. André;Y. Soumare;J. Piquemal;G. Viau;C. Gatel-C.-Gate
报道了Co(=15 nm，=130 nm)纳米线的磁性。在氧化丝中，我们测量了T~100K以下0.1T量级的大交换偏置场。铁磁磁芯和反铁磁性CoO壳层之间的交换偏置开始时，伴随着0.2T的矫顽力下降，导致在100$K处的矫顽力最小。磁化驰豫测量表明，S的磁粘性与温度有关，这与CoO表面CoO颗粒的体积分布一致。我们认为反铁磁性CoO壳层的超顺磁性涨落在纳米线磁化反转中起着关键作用，并解释了矫顽力下降的原因。这一点得到了微磁模拟的支持。这一行为是一维系统特有的，它具有很大的形状各向异性，并且以前在具有高度对称性和低矫顽力的0D(球)或2D(薄膜)系统中没有观察到。这项研究强调了原子力显微镜超顺磁涨落在交换偏置机制中的重要性。
The magnetic properties of Co ( =15 nm, =130nm) nanowires are reported. In oxidized wires, we measure large exchange bias fields of the order of 0.1 T below T ~ 100 K. The onset of the exchange bias, between the ferromagnetic core and the anti-ferromagnetic CoO shell, is accompanied by a coercivity drop of 0.2 T which leads to a minimum in coercivity at $\sim100$ K. Magnetization relaxation measurements show a temperature dependence of the magnetic viscosity S which is consistent with a volume distribution of the CoO grains at the surface. We propose that the superparamagnetic fluctuations of the anti-ferromagnetic CoO shell play a key role in the flipping of the nanowire magnetization and explain the coercivity drop. This is supported by micromagnetic simulations. This behavior is specific to the geometry of a 1D system which possesses a large shape anisotropy and was not previously observed in 0D (spheres) or 2D (thin films) systems which have a high degree of symmetry and low coercivities. This study underlines the importance of the AFM super-paramagnetic fluctuations in the exchange bias mechanism.