The James Franck Institute and Department of Physics, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA.
Proc Natl Acad Sci U S A. 2010 Feb 16;107(7):2797-800. doi: 10.1073/pnas.0910575107. Epub 2010 Jan 29.
The intended use of a magnetic material, from information storage to power conversion, depends crucially on its domain structure, traditionally crafted during materials synthesis. By contrast, we show that an external magnetic field, applied transverse to the preferred magnetization of a model disordered uniaxial ferromagnet, is an isothermal regulator of domain pinning. At elevated temperatures, near the transition into the paramagnet, modest transverse fields increase the pinning, stabilize the domain structure, and harden the magnet, until a point where the field induces quantum tunneling of the domain walls and softens the magnet. At low temperatures, tunneling completely dominates the domain dynamics and provides an interpretation of the quantum phase transition in highly disordered magnets as a localization/delocalization transition for domain walls. While the energy scales of the rare earth ferromagnet studied here restrict the effects to cryogenic temperatures, the principles discovered are general and should be applicable to existing classes of highly anisotropic ferromagnets with ordering at room temperature or above.
磁性材料的预期用途，从信息存储到能量转换，都取决于其畴结构，畴结构通常在材料合成过程中形成。相比之下，我们表明，施加于各向异性无序铁磁体的优选磁化方向横向的外磁场是各向同性的畴钉扎调节剂。在接近顺磁体转变的高温下，适度的横向磁场会增加钉扎，稳定畴结构，并使磁体变硬，直到磁场诱导畴壁的量子隧穿并使磁体软化。在低温下，隧穿完全主导了畴的动力学，并为高度无序磁体中的量子相变提供了一种解释，即畴壁的局域/离域转变。虽然这里研究的稀土铁磁体的能量尺度将这些影响限制在低温范围内，但所发现的原理是普遍的，应该适用于室温或以上有序的现有各向异性铁磁体类别。
