Okinawa Institute of Science and Technology, Kunigami, Okinawa 904-0411, Japan.
Nat Nanotechnol. 2010 Jan;5(1):37-41. doi: 10.1038/nnano.2009.342. Epub 2009 Nov 29.
Colossal magnetoresistance is a dramatic decrease in resistivity caused by applied magnetic fields, and has been the focus of much research because of its potential for magnetic data storage using materials such as manganites. Although extensive microscopy and theoretical studies have shown that colossal magnetoresistance involves competing insulating and ferromagnetic conductive phases, the mechanism underlying the effect remains unclear. Here, by directly observing magnetic domain walls and flux distributions using cryogenic Lorentz microscopy and electron holography, we demonstrate that an applied magnetic field assists nucleation and growth of an ordered ferromagnetic phase. These results provide new insights into the evolution dynamics of complex domain structures at the nanoscale, and help to explain anomalous phase separation phenomena that are relevant for applications. Our approach can also be used to determine magnetic parameters of nanoscale regions, such as magnetocrystalline anisotropy and exchange stiffness, without bulk magnetization results or neutron scattering data.
巨磁电阻是一种由外加磁场引起的电阻率急剧下降的现象，由于其在使用锰氧化物等材料进行磁数据存储方面的潜力，因此一直是研究的焦点。尽管广泛的显微镜和理论研究表明，巨磁电阻涉及竞争的绝缘和铁磁导电相，但该效应的机制仍不清楚。在这里，我们通过使用低温洛伦兹显微镜和电子全息术直接观察磁畴壁和磁通分布，证明了外加磁场有助于有序铁磁相的成核和生长。这些结果为纳米尺度上复杂畴结构的演化动力学提供了新的见解，并有助于解释与应用相关的异常相分离现象。我们的方法还可以用于确定纳米区域的磁参数，例如磁各向异性和交换弹性，而无需块状磁化结果或中子散射数据。
