Onset of ferromagnetism in Fe epitaxially grown on GaAs(001) (4×2) and (2×6)
Onset of ferromagnetism in Fe epitaxially grown on GaAs(001) (4×2) and (2×6)
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DOI：
10.1063/1.1361258
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发表时间：
2001-06
影响因子：
3.2
通讯作者：
F. Bensch;G. Garreau;R. Moosbühler;G. Bayreuther;E. Beaurepaire
中科院分区：
文献类型：
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作者：
F. Bensch;G. Garreau;R. Moosbühler;G. Bayreuther;E. Beaurepaire
在室温下，在GaAs（001）上外延生长超薄Fe薄膜，其表面重构为显性（4×2）或显性（2×6）。在tFe小于2.8单层（ML）的标称铁覆盖率下，在特定临界温度TC下观察到铁磁状态。令人惊讶的是，TC的磁相变比金属单晶衬底上的铁薄膜更明显，这被认为是二维（2D）铁磁体的优秀代表。这可能是由于薄膜不均匀性的横向长度尺度极短。临界指数β=0.26接近有限尺寸的二维XY系统的期望值。当tFe=3.6 ML时，TC接近室温。随着铁覆盖率的降低，TC急剧下降，平均斜率为270 K/ML。从幂律推断，在tFe=2.5 ML时，TC似乎消失了。在tFe=2.5 ML时，铁磁性的开始被解释为铁岛聚并过程中的渗透现象。
Ultrathin Fe films were epitaxially grown at room temperature on GaAs(001) with either predominant (4×2) or (2×6) surface reconstruction. At nominal Fe coverages of tFe⩾2.8 monolayers (ML), a ferromagnetic state is observed below a certain critical temperature, TC. Surprisingly, the magnetic phase transition at TC appears even sharper than for Fe films on metallic single-crystal substrates, which were believed to be an excellent representation of two-dimensional (2D) ferromagnets. This may be due to the extremely short lateral length scale of film inhomogeneities. The critical exponent β=0.26 is close to the value expected for 2D XY systems of finite size. For tFe=3.6 ML, TC is close to room temperature. TC decreases steeply with decreasing Fe coverage, with an average slope of 270 K/ML. From a power law extrapolation, TC seems to vanish at tFe=2.5 ML. The onset of ferromagnetism at tFe=2.5 ML is interpreted as a percolation phenomenon during the coalescence process of Fe islands.