Fabrication and study of magnetic competing systems in artificial superlattices

在本研究中，利用人工超晶格制造了磁竞争，关于磁反各向异性或交换耦合，系统。研究了它们的磁性能，以发现由于磁竞争而产生的新磁相。在平行于hcp结构c轴生长的Er/Tb单晶超晶格中实现了磁各向异性竞争的磁体系。中子衍射研究表明，平行于c轴的自旋组分与体Er的Neel和Curie温度序列相同，而基面上的自旋组分在更高温度下保持螺旋有序，最高温度为体Er相应温度的两倍以上，达到130K。我们认为相邻Tb层的基面铁磁有序增强了Er层基面有序的发展。为了研究具有交换偶联竞争的磁性体系，在单晶基底上制备了FeF_2/ZnF_2氟化超晶格。除了密切的结构表征外，还研究了Neel温度与FeF_2（001）和（110）超薄层厚度的关系。从J_2和J_3相互竞争交换耦合引起的界面形貌挫折的角度讨论了观察到的Neel温度在1原子单层周期内的周期性变化。与Fe_xZn_<1-x>F_2的体稀释体系相比，这些超晶格可以看作是“受控竞争体系”。

In this study, fabrication of the magnetic competing, with respect to magnetic antisotropy or exchange-coupling, systems was performed using artificial superlattices. Their magnetic properties were investigated in order to find out novel magnetic phases due to the magnetic competition. The magnetic systems with the competition in magnetic anisotropy were realized in the single-crystal Er/Tb superlattices grown parallel to the c-axis of hcp structure. Neutron diffraction study revealed that, as a function of temperature, the spin component parallel to the c-axis undergoes the same sequence including the Neel and Curie temperatures as bulk Er, while the component in the basal plane retains a helical ordering at higher temperatures up to 130K, which is more than twice the corresponding temperature of bulk Er. We argued that the basal-plane ferromagnetic ordering of the adjacent Tb layers enhanced the development of the basal-plane ordering in the Er layers. In order to study the magnetic systems with the competition in exchange-coupling, fluoride superlattices of FeF_2/ZnF_2 were prepared on single-crystal substrates. In addition to close structural characterization, dependence of the Neel temperature on the thickness of the FeF_2(001) and (110) ultra-thin layers was investigated. The observed periodic variations of the Neel temperature with a period of 1 atomic monolayer were discussed in terms of an interface-topographical frustration due to the competing exchange-coupling of J_2 and J_3. These superlattices can be regarded as "controlled competing systems" in contrast to the bulk dilute system of Fe_xZn_<1-x>F_2.