Krüger F, Pedder C J, Green A G
London Centre for Nanotechnology, University College London, Gordon Street, London WC1H 0AH, United Kingdom and ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom.
London Centre for Nanotechnology, University College London, Gordon Street, London WC1H 0AH, United Kingdom.
Phys Rev Lett. 2014 Oct 3;113(14):147001. doi: 10.1103/PhysRevLett.113.147001.
We demonstrate that the interplay between soft electronic particle-hole fluctuations and magnetic anisotropies can drive ferromagnetic moments to point along a magnetic hard axis. As a proof of concept, we show this behavior explicitly for a generic two-band model with local Coulomb and Hund's interactions and a spin-orbit-induced easy plane anisotropy. The phase diagram is calculated within the fermionic quantum order-by-disorder approach, which is based on a self-consistent free-energy expansion around a magnetically ordered state with unspecified orientation. Quantum fluctuations render the transition of the easy-plane ferromagnet first order below a tricritical point. At even lower temperatures, directionally dependent transverse fluctuations dominate the magnetic anisotropy, and the moments flip to lie along the magnetic hard axis. We discuss our findings in the context of recent experiments that show this unusual ordering along the magnetic hard direction.
我们证明，软电子粒子-空穴涨落与磁各向异性之间的相互作用可驱使铁磁矩沿磁硬轴方向排列。作为概念验证，我们针对具有局域库仑相互作用和洪德相互作用以及自旋轨道诱导易平面各向异性的一般两能带模型，明确展示了这种行为。相图是在费米子量子无序致序方法内计算得出的，该方法基于围绕具有未指定取向的磁有序态的自洽自由能展开。量子涨落在三临界点以下使易平面铁磁体的转变成为一级相变。在更低温度下，方向依赖的横向涨落主导磁各向异性，并且磁矩翻转至沿磁硬轴排列。我们在近期实验的背景下讨论我们的发现，这些实验展示了沿磁硬方向的这种不寻常的有序排列。
