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arXiv 1312.3136cond-mat.str-elcond-mat.mes-hallcond-mat.mtrl-scicond-mat.stat-mech
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反铁磁体表面的明显磁相变

Distinct magnetic phase transition at the surface of an antiferromagnet

Sean Langridge, Gavin M. Watson, Doon Gibbs, Joseph J. Betouras, Nikitas I. Gidopoulos, Frank Pollmann, Martin W. Long, Christian Vettier, Gerry H. Lander

摘要:

在大多数磁系统中,表面需要在与主体相同的温度下有序。在本研究中,我们报告了一个独特的和意想不到的表面磁相变,唯一的温度低于内尔温度。利用掠入射X射线共振磁散射技术,我们观察了二氧化铀的近表面行为。UO $_2$是一种非共线的三重q反铁磁体,其U离子位于面心立方晶格上。理论研究表明,在表面处,由于失去键,当表面附近的自旋旋转时,能量增加减少,逐渐失去其与表面分量的法线。在表面,最低能量的自旋组态具有双q(平面)结构。随着温度的升高,热波动使表面处的面内晶体场各向异性饱和,导致具有铁磁$XY$特性并且与体相解耦的软激发。有限的二维$XY$模型的结构因子,适合的散射强度的几个数量级的实验数据。我们的研究结果支持一个明显的磁过渡在表面的Kosterlitz无磁普适性类。

英文摘要:

In the majority of magnetic systems the surface is required to order at the same temperature as the bulk. In the present study, we report a distinct and unexpected surface magnetic phase transition, uniquely at a lower temperature than the Néel temperature. Employing grazing incidence X-ray resonant magnetic scattering we have observed the near surface behavior of uranium dioxide. UO$_2$ is a non-collinear, triple-q, antiferromagnet with the U ions on an face-centered-cubic lattice. Theoretical investigations establish that at the surface the energy increase, due to the lost bonds, reduces when the spins near the surface rotate, gradually losing their normal to the surface component. At the surface the lowest-energy spin configuration has a double-q (planar) structure. With increasing temperature, thermal fluctuations saturate the in-plane crystal field anisotropy at the surface, leading to soft excitations that have ferromagnetic $XY$ character and are decoupled from the bulk. The structure factor of a finite two-dimensional $XY$ model, fits the experimental data well for several orders of magnitude of the scattered intensity. Our results support a distinct magnetic transition at the surface in the Kosterlitz-Thouless universality class.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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