X-ray absorption and magnetic circular dichroism of LaCoO3, La0.7Ce0.3CoO3, and La0.7Sr0.3CoO3 films: Evidence for cobalt-valence-dependent magnetism
X-ray absorption and magnetic circular dichroism of LaCoO3, La0.7Ce0.3CoO3, and La0.7Sr0.3CoO3 films: Evidence for cobalt-valence-dependent magnetism
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DOI：
10.1103/physrevb.82.174416
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发表时间：
2010-11-11
影响因子：
3.7
通讯作者：
Schuppler, S.
中科院分区：
文献类型：
--
作者：
Merz, M.;Nagel, P.;Schuppler, S.
未掺杂LaCoO_3、电子掺杂La_(0.7)Ce_(0.3)CoO_3和空穴掺杂La_(0.7)Sr_(0.3)CoO_3外延薄膜具有铁磁性，其转变温度T-C分别接近84K、23K和194K。用软X射线磁性圆二色谱和近边X射线吸收精细结构研究了这些化合物的自旋态结构，包括Co、L-2、L-3和O K边。结果表明，Co3+高自旋态和Co3+低自旋态之间的超交换导致了LaCoO_3的铁磁性。对于La0.7Ce0.3CoO_3，Co3+离子处于低自旋态，自旋和轨道矩主要由Co2+的高自旋组态决定。自旋阻塞自然解释了La0.7Ce0.3CoO_3的低转变温度和绝缘特性。另一方面，对于La0.7Sr0.3CoO_3，外延薄膜中的磁矩来源于高自旋Co3+和高自旋Co4+态。铁磁性是由两个高自旋组态之间的t(2g)双交换引起的。对于所有的系统，都观察到了很强的磁各向异性，磁矩基本上取向在薄膜平面内。
Epitaxial thin films of undoped LaCoO3, of electron-doped La0.7Ce0.3CoO3, and of hole-doped La0.7Sr0.3CoO3 exhibit ferromagnetic order with a transition temperature T-C approximate to 84 K, 23 K, and 194 K, respectively. The spin-state structure for these compounds was studied by soft x-ray magnetic circular dichroism and by near-edge x-ray absorption fine structure at the Co L-2,L-3 and O K edges. It turns out that superexchange between Co3+ high-spin and Co3+ low-spin states is responsible for the ferromagnetism in LaCoO3. For La0.7Ce0.3CoO3 the Co3+ ions are in a low-spin state and the spin and orbital moments are predominantly determined by a Co2+ high-spin configuration. A spin blockade naturally explains the low transition temperature and the insulating characteristics of La0.7Ce0.3CoO3. For La0.7Sr0.3CoO3, on the other hand, the magnetic moments in the epitaxial films originate from high-spin Co3+ and high-spin Co4+ states. Ferromagnetism is induced by t(2g) double exchange between the two high-spin configurations. For all systems, a strong magnetic anisotropy is observed, with the magnetic moments essentially oriented within the film plane.