Lucas Irene, Marcano Noelia, Prokscha Thomas, Magén César, Corcuera Rubén, Morellón Luis, De Teresa José M, Ibarra M Ricardo, Algarabel Pedro A
Instituto de Nanociencia y Materiales de Aragón (INMA), CSIC-Universidad de Zaragoza, 50009 Zaragoza, Spain.
Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50009 Zaragoza, Spain.
Nanomaterials (Basel). 2022 Oct 18;12(20):3646. doi: 10.3390/nano12203646.
Epitaxial strain modifies the physical properties of thin films deposited on single-crystal substrates. In a previous work, we demonstrated that in the case of LaCaMnO thin films the strain induced by the substrate can produce the segregation of a non-ferromagnetic layer (NFL) at the top surface of ferromagnetic epitaxial LaCaMnO for a critical value of the tetragonality τ, defined as = | - |, of τ ≈ 0.024. Although preliminary analysis suggested its antiferromagnetic nature, to date a complete characterization of the magnetic state of such an NFL has not been performed. Here, we present a comprehensive magnetic characterization of the strain-induced segregated NFL. The field-cooled magnetic hysteresis loops exhibit an exchange bias mechanism below T ≈ 80 K, which is well below the Curie temperature of the ferromagnetic LaCaMnO layer. The exchange bias and coercive fields decay exponentially with temperature, which is commonly accepted to describe spin-glass (SG) behavior. The signatures of slow dynamics were confirmed by slow spin relaxation over a wide temperature regime. Low-energy muon spectroscopy experiments directly evidence the slowing down of the magnetic moments below ~100 K in the NFL. The experimental results indicate the SG nature of the NFL. This SG state can be understood within the context of the competing ferromagnetic and antiferromagnetic interactions of similar energies.
外延应变会改变沉积在单晶衬底上的薄膜的物理性质。在之前的一项工作中，我们证明了对于LaCaMnO薄膜，在衬底诱导的应变作用下，当四方度τ（定义为τ = |a - c| / a，其中a和c分别为晶格常数）的临界值约为0.024时，铁磁外延LaCaMnO薄膜的顶表面会产生一个非铁磁层（NFL）的偏析。尽管初步分析表明其具有反铁磁性质，但迄今为止尚未对这种NFL的磁态进行完整表征。在此，我们给出了应变诱导偏析NFL的全面磁学表征。场冷磁滞回线在T ≈ 80 K以下呈现出交换偏置机制，该温度远低于铁磁LaCaMnO层的居里温度。交换偏置场和矫顽场随温度呈指数衰减，这通常被认为是描述自旋玻璃（SG）行为的特征。在很宽的温度范围内，慢自旋弛豫证实了慢动力学的特征。低能μ子谱实验直接证明了NFL中磁矩在~100 K以下的减慢。实验结果表明NFL具有SG性质。这种SG态可以在具有相似能量的竞争铁磁和反铁磁相互作用的背景下得到理解。
