Controlling the structural transition at the Neel point of CrN epitaxial thin films using epitaxial growth
Controlling the structural transition at the Neel point of CrN epitaxial thin films using epitaxial growth
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DOI：
10.1103/physrevb.75.054416
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发表时间：
2007-02-01
影响因子：
3.7
通讯作者：
Yamanaka, Shoji
中科院分区：
文献类型：
--
作者：
Inumaru, Kei;Koyama, Kunihiko;Yamanaka, Shoji
采用脉冲激光沉积法在α-Al 2 O3（0001）和MgO（001）基片上外延生长了氮化铬（CrN）薄膜，并利用控温X射线衍射实验研究了CrN薄膜在Neel温度附近（近似270 K）的结构变化。已知大块立方CrN在低于尼尔温度时显示单斜畸变。在MgO（001）衬底上生长的CrN薄膜，CrN（001）面平行于衬底表面，在260 K左右出现明显的结构变化。另一方面，在α-Al 2 O3（0001）衬底上，CrN相以其（111）面平行于衬底表面生长，并且在Neel温度下没有显示出结构变化。不同取向的外延膜可以解释不同的行为：体CrN的结构转变导致原子间距离和键角在（111）平面上变化很大，但在（001）平面上变化不大。在薄膜的情况下，α-Al_2 O_3（0001）衬底表面可以通过固定膜的CrN（111）界面上的原子位置来防止（111）取向膜的结构畸变。根据薄膜的结构行为，α-Al_2 O_3（0001）上的（111）取向的CrN薄膜在Neel温度附近没有显示出金属导电性的异常。另一方面，MgO上的（001）取向的CrN显示出电导率的急剧增加，伴随着低于Neel点的晶格畸变。这些结果突出了一个例子，外延可以用来控制结构转变的存在，进一步伴随着反铁磁有序，这是密切相关的材料的电子性质。
Chromium nitride (CrN) films were epitaxially grown on alpha-Al2O3(0001) and MgO (001) substrates by pulsed laser deposition at 973 K under nitrogen radical irradiation, and the structural change of the films was investigated at around the Neel temperature of CrN (similar to 270 K) by temperature-controlled x-ray diffraction experiments. Bulk cubic CrN is known to show monoclinic distortion below the Neel temperature. The CrN film grown on MgO(001) with the CrN(001) plane parallel to the substrate surface, exhibited a clear structural change at around 260 K. On the other hand, on alpha-Al2O3(0001) substrates, the CrN phase grew with its (111) planes parallel to the substrate surface, and showed no structural change at the Neel temperature. The different orientation of the epitaxial films can explain the different behavior of the films: The structural transition of bulk-CrN causes large variations in the interatomic distances and bond angles on the (111) plane, but varies little on the (001) plane. In the case of thin films, the alpha-Al2O3(0001) substrate surface could prevent the (111)-oriented film from distorting its structure by fixing atom positions on the CrN(111) interfaces of the film. In accordance with the structural behavior of the films, the (111)-oriented CrN film on alpha-Al2O3(0001) showed no anomaly in its metallic conductivity around the Neel temperature. On the other hand, the (001)-oriented CrN on MgO showed a steep increase in electrical conductivity, accompanied by a lattice distortion below the Neel point. These results highlight an example that epitaxy could be used to control the existence of structural transitions, further accompanied by an antiferromagnetic ordering, which is closely related to the electronic properties of materials.