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中国物理学会期刊

SrRuO3超薄膜制备条件和拓扑霍尔效应的关联

CSTR: 32037.14.aps.72.20221854

Correlation of preparation conditions of SrRuO3 ultrathin films with topological Hall effect

CSTR: 32037.14.aps.72.20221854
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  • 使用激光分子束外延在SrTiO3(001)衬底上生长SrRuO3薄膜, 并研究激光能量密度、生长温度和靶材表面烧蚀度等生长参数对于SrRuO3表面形貌、基本磁电性质以及拓扑霍尔效应的影响. 当在最优条件下生长SrRuO3薄膜时, 样品表面平整、台阶清晰, 具有最低的金属-绝缘体转变温度, 电阻率最低, 且具有最显著的拓扑霍尔效应; 而改变生长参数生长的SrRuO3薄膜由于存在更多的缺陷, 其表面较粗糙, 金属-绝缘体转变温度增大, 或表现出绝缘体行为, 而拓扑霍尔效应会变弱甚至消失.

     

    As one of the magnetic transition metal oxides, SrRuO3 (SRO) has received much attention in recent years, which is mainly due to its unique itinerate ferromagnetism and the unusual electrical transport properties–behaving as Fermi liquid at low temperature and bad metal at high temperature. In the growth of SRO thin films, there are many factors that can affect the quality of thin films. In this work, we study various factors affecting the growth and quality of SRO thin films by using laser molecular beam epitaxy (laser MBE), including laser energy density, substrate temperature and target surface conditions, and explore their influences on the topological Hall effect (THE) in SRO. For thin films grown at high laser energy density and high temperature, we found that there are large trenches at the edge of steps, which deteriorate the transport properties of the thin films. When using low laser energy density, extra SrO may exist in the films, which also suppresses the conductivity. Films grown at low temperature tend to have poor crystallinity while films grown at high temperature exhibit island structures. The ablation degree of the target surface increases the decomposition of SRO to SrO, Ru and volatile RuO4, resulting in Ru defects in the grown thin film. The SRO thin film grown under the optimal conditions (1.75 J·cm–2, 670 ℃, fresh target surface) exhibits the optimal conductivity and the strongest THE. For non-optimal growth conditions that favors thickness inhomogeneity or Ru defects in the film, THE becomes weaker or even disappears. Therefore, we believe that the THE is due to the Dzyaloshinskii-Moriya interaction (DMI) resulting from the interfacial inversion asymmetry and the associated chiral spin structures.

     

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