arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1909.02153cond-mat.mtrl-sci
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自旋无隙半导体Mn $_2$ CoAl中的无序研究

Exploring Disorder in the Spin Gapless Semiconductor Mn$_2$CoAl

Robert G. Buckley, Tane Butler, Catherine Pot, Nicholas M. Strickland, Simon Granville

摘要:

自从Heusler化合物Mn $_2$ CoAl中自旋无隙半导体行为的预测以来,薄膜中自旋无隙行为的证据通常从磁输运测量中推断。然而,自旋无隙状态是脆弱的,进一步,能带结构计算表明,即使是少量的原子无序可能会破坏it.To探索的Mn $_2$ CoAl的性质的影响,无序,我们进行了实验研究的结构,磁输运和光学性质从远红外到紫外线,直流磁控溅射Mn $_2$ CoAl薄膜。一个非常短的平均自由程,晶格间距的顺序,从DC传输数据中提取。测量了200 $μ$ $Ω$ cm的室温电阻率以及在4和400 K之间的小且负的电阻温度系数。我们注意到,这种量级的参数经常在无序金属中观察到。我们发现这种行为是很好地描述了一个弱的本地化模型,一个结果,支持由一个大的德鲁德贡献的光学响应,其中一个高的散射率是派生出来的,这是等于从直流电导率和霍尔效应数据派生的值。我们还注意到文献中报道的Mn $_2$ CoAl薄膜的磁输运行为之间的强烈相似性,包括我们的。我们的结论是,基于实验数据之间的比较,和最近的能带结构计算,明确包括无序,作为制备的Mn $_2$ CoAl薄膜最好描述为无序金属,而不是自旋无隙半导体。

英文摘要:

Since the prediction of spin-gapless semiconducting behaviour in the Heusler compound Mn$_2$CoAl, evidence of spin-gapless behaviour in thin films has typically been inferred from magnetotransport measurements. The spin gapless state is however fragile, and further, band structure calculations indicate that even a small amount of atomic disorder may destroy it. To explore the impact of disorder on the properties of Mn$_2$CoAl, we have undertaken an experimental study of the structural, magnetotransport and optical properties from the far infrared to the UV, on DC magnetron sputtered Mn$_2$CoAl thin films. A very short mean free path, of the order of a lattice spacing, is extracted from the DC transport data. A room temperature resistivity of 200 $μ$$Ω$cm along with a small and negative temperature coefficient of resistance between 4 and 400 K was measured. We note that parameters of this magnitude are often observed in disordered metals. We find this behaviour is well described by a weak localisation model, a result that is supported by a large Drude contribution to the optical response, where a high scattering rate is derived, which is equal to the value derived from the DC conductivity and Hall effect data. We also note the strong similarities between the magnetotransport behaviour reported for Mn$_2$CoAl films in the literature, including ours. We conclude that, based on comparisons between the experimental data, and recent band structure calculations that explicitly include disorder, as-prepared Mn$_2$CoAl films are best described as a disordered metal, rather than a spin gapless semiconductor.

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