Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 7610001, Israel.
NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 117456, Singapore.
Nat Commun. 2016 Aug 25;7:12566. doi: 10.1038/ncomms12566.
Atomically sharp oxide heterostructures exhibit a range of novel physical phenomena that are absent in the parent compounds. A prominent example is the appearance of highly conducting and superconducting states at the interface between LaAlO3 and SrTiO3. Here we report an emergent phenomenon at the LaMnO3/SrTiO3 interface where an antiferromagnetic Mott insulator abruptly transforms into a nanoscale inhomogeneous magnetic state. Upon increasing the thickness of LaMnO3, our scanning nanoSQUID-on-tip microscopy shows spontaneous formation of isolated magnetic nanoislands, which display thermally activated moment reversals in response to an in-plane magnetic field. The observed superparamagnetic state manifests the emergence of thermodynamic electronic phase separation in which metallic ferromagnetic islands nucleate in an insulating antiferromagnetic matrix. We derive a model that captures the sharp onset and the thickness dependence of the magnetization. Our model suggests that a nearby superparamagnetic-ferromagnetic transition can be gate tuned, holding potential for applications in magnetic storage and spintronics.
原子级锐利的氧化物异质结构表现出一系列在母体化合物中不存在的新奇物理现象。一个突出的例子是 LaAlO3 和 SrTiO3 之间界面上出现的高导电性和超导状态。在这里，我们报告了在 LaMnO3/SrTiO3 界面上出现的一种新现象，其中反铁磁莫特绝缘体突然转变为纳米级的非均匀磁态。随着 LaMnO3 厚度的增加，我们的扫描纳米 SQUID 尖端显微镜显示出孤立的磁性纳米岛的自发形成，这些纳米岛在面内磁场下表现出热激活的磁矩反转。观察到的超顺磁状态表明热力学电子相分离的出现，其中金属铁磁岛在绝缘反铁磁基体中形核。我们提出了一个模型，该模型捕获了磁化的急剧起始和厚度依赖性。我们的模型表明，附近的超顺磁-铁磁转变可以通过栅极调谐，这为磁存储和自旋电子学的应用提供了潜力。
