Magnetic field control of insulator-metal crossover in cobaltite films via thermally activated percolation
Magnetic field control of insulator-metal crossover in cobaltite films via thermally activated percolation
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DOI：
10.1103/physrevb.106.155135
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发表时间：
2022-10
影响因子：
3.7
通讯作者：
Meng Wang;K. Matsuura;M. Nakamura;M. Sawada;M. Kawasaki;F. Kagawa
中科院分区：
文献类型：
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作者：
Meng Wang;K. Matsuura;M. Nakamura;M. Sawada;M. Kawasaki;F. Kagawa
双交换跳跃和库仑排斥之间的竞争是混合价锰氧化物中肥沃现象的基础，例如与磁场驱动的绝缘体-金属转变（IMT）相关的巨磁阻。相比之下，类似的双交换系统，钙钛矿钴酸盐，然而，表现出小得多的磁阻，和绝缘体到金属相的演变与场刺激仍然难以捉摸。在这里，我们揭示了一个亚微米级的相分离和磁场控制的交叉类IMT在拉伸应变膜。我们的运输，磁化和磁力显微镜测量表明，虽然IMT几乎没有诱导下的等温场扫描，它出现在通过热激活的铁磁畴渗流场冷却。这种依赖于相变历史的性质意味着与微观相分离相关的非遍历特征。通过进一步比较从Ca、Sr到Ba的具有AE的薄膜的输运性质，我们揭示了在这些薄膜中普遍存在非遍历行为，并且混合自旋态是在畴渗透期间增强畴壁运动的能垒的关键因素。锰氧化物中不存在这种自旋态自由度，这可能导致钴氧化物和锰氧化物在磁场诱导IMT中的相演化动力学存在很大差异。
Competition between the double-exchange hopping and Coulomb repulsion underlies fertile phenomena in mixed-valent manganites, such as colossal magnetoresistance associated with a magnetic-field-driven insulator-metal transition (IMT). In contrast, an analogous double-exchange system, perovskite cobaltites, however, shows much smaller magnetoresistance, and the insulator-to-metal phase evolution with field stimulus remains elusive. Here, we unveil a submicrometer-scale phase separation and magnetic-field-controlled crossoverlike IMT in a tensile-strainedfilm. Our transport, magnetization, and magnetic-force-microscopy measurements reveal that, although the IMT is barely induced under an isothermal field sweep, it emerges under field cooling through a thermally activated ferromagnetic domain percolation. Such thermodynamic-history-dependent properties signify a nonergodic feature associated with the microscopic phase separation. By further comparing the transport properties amongfilms with AE from Ca, Sr, to Ba, we reveal that the nonergodic behavior prevails in these films and that the mixed spin states are a key factor to enhance the energy barrier for domain-wall motions during domain percolation. Such a spin-state degree of freedom is absent in manganites, probably resulting in the large difference of the phase evolution kinetics in the magnetic-field-induced IMT between cobaltites and manganites.