铁磁薄膜中的多极相互作用和复杂相
Multipolar interactions and complex phases in ferromagnetic ultrathin films
摘要：
我们提出了一个模型来描述在介观尺度下观察到的复杂相的磁性薄膜。该模型是基于偶极以及四极磁矩之间的相互作用。在强垂直晶体各向异性的特殊情况下，我们表明，四极自由度与畴壁的取向是必不可少的，以正确地描述所观察到的畴形成的现象。预测了以畴壁（条纹状）的取向顺序为特征但没有平移顺序的取向相。在热力学极限下，这种各向同性-相变属于Kosterlitz-无相变类型。然而，我们发现，在实际的实验尺度下，序参量的波动是正则化的样本大小，和取向的长程序，预测的平均场，应该是可观察的。该过渡可以完全通过测量磁结构因子以及非线性面内磁化率来实验表征。
英文摘要：
We present a model to describe complex phases observed at mesoscopic scales in ultrathin magnetic films. The model is based on the interaction between dipolar as well as quadrupolar magnetic moments. In the special case of strong perpendicular crystal anisotropy, we show that quadrupolar degrees of freedom associated with orientation of domain walls are essential in order to correctly describe the observed phenomenology of domain formation. A nematic phase characterized by orientational order of domain walls (stripe-like) but without translational order is predicted. This isotropic-nematic transition belongs to the Kosterlitz-Thouless type in the thermodynamic limit. However, we found that in actual experimental scales, the fluctuations of the nematic order parameter are regularized by the sample size, and orientational long range order, as predicted by mean field, should be observable. The transition may be completely characterized experimentally from measurements of the magnetic structure factor as well as from the non-linear in-plane magnetic susceptibility.
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