Spin Resolution and Evidence for Superexchange on NiO(001) Observed by Force Microscopy
Spin Resolution and Evidence for Superexchange on NiO(001) Observed by Force Microscopy
复制标题
DOI：
10.1103/physrevlett.110.266101
复制
发表时间：
2013-06-24
影响因子：
8.6
通讯作者：
Giessibl, Franz J.
中科院分区：
文献类型：
--
作者：
Pielmeier, Florian;Giessibl, Franz J.
采用非接触式原子力显微镜，在4.4 K下，利用安装在qPlus传感器上的块铁和SmCo尖端，在低于50 pm的振幅下振荡，解决了氧化镍（001）表面的自旋顺序。依赖自旋的信号很难被铁尖探测到。相比之下，SmCo尖端对具有相反自旋的Ni离子产生1.35 pm的高度对比。SmCo尖端甚至在2 x 1自旋单元胞内0.5 pm的O原子上显示出很小的高度对比，表明观察到了超交换。我们将信噪比的增加归因于SmCo的磁晶各向异性能量的增加，这使得磁矩在顶点处稳定。在Ni向上箭头，Ni向下箭头和O晶格位置上的原子力谱显示，在最近的可达距离上，交换能的大小仅为1 meV，指数衰减长度为λ (exe) = 18 pm。
The spin order of the nickel oxide (001) surface is resolved, employing noncontact atomic force microscopy at 4.4 K using bulk Fe and SmCo tips mounted on a qPlus sensor that oscillates at sub-50 pm amplitudes. The spin-dependent signal is hardly detectable with Fe tips. In contrast, SmCo tips yield a height contrast of 1.35 pm for Ni ions with opposite spins. SmCo tips even show a small height contrast on the O atoms of 0.5 pm within the 2 x 1 spin unit cell, pointing to the observation of superexchange. We attribute the increased signal-to-noise ratio to the increased magnetocrystalline anisotropy energy of SmCo, which stabilizes the magnetic moment at the apex. Atomic force spectroscopy on the Ni up arrow, Ni down arrow, and O lattice site reveals a magnitude of the exchange energy of merely 1 meV at the closest accessible distance with an exponential decay length of lambda(exe) = 18 pm.