Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA.
Phys Rev Lett. 2012 Nov 9;109(19):197202. doi: 10.1103/PhysRevLett.109.197202. Epub 2012 Nov 7.
We have found ferromagnetism in epitaxially grown superlattices of CaRuO(3)/CaMnO(3) that arises in one unit cell at the interface. Scanning transmission electron microscopy and electron energy loss spectroscopy indicate that the difference in magnitude of the Mn valence states between the center of the CaMnO(3) layer and the interface region is consistent with double exchange interaction among the Mn ions at the interface. Polarized neutron reflectivity and the CaMnO(3) thickness dependence of the exchange bias field together indicate that the interfacial ferromagnetism is only limited to one unit cell of CaMnO(3) at each interface. The interfacial moment alternates between the 1 μ(B)/interface Mn ion for even CaMnO(3) layers and the 0.5 μ(B)/interface Mn ion for odd CaMnO(3) layers. This modulation, combined with the exchange bias, suggests the presence of a modulating interlayer coupling between neighboring ferromagnetic interfaces via the antiferromagnetic CaMnO(3) layers.
我们在外延生长的 CaRuO(3)/CaMnO(3)超晶格中发现了铁磁性，这种铁磁性出现在界面的一个单元胞中。扫描透射电子显微镜和电子能量损失谱表明，CaMnO(3)层中心和界面区域之间 Mn 价态的大小差异与界面处 Mn 离子的双交换相互作用一致。极化中子反射率和交换偏置场随 CaMnO(3)厚度的变化共同表明，界面铁磁性仅局限于每个界面的 CaMnO(3)的一个单元胞。界面磁矩在偶数 CaMnO(3)层的每个界面 Mn 离子为 1 μ(B)/界面 Mn 离子和奇数 CaMnO(3)层的每个界面 Mn 离子为 0.5 μ(B)/界面 Mn 离子之间交替。这种调制，结合交换偏置，表明通过反铁磁 CaMnO(3)层，相邻铁磁界面之间存在调制的层间耦合。
