Mohammed Wael M, Yanilkin Igor V, Gumarov Amir I, Kiiamov Airat G, Yusupov Roman V, Tagirov Lenar R
Kazan Federal University, Kremlyovskaya str. 18, 420008 Kazan, Russia.
E. K. Zavoisky Physical-Technical Institute, FRC Kazan Scientific Centre of RAS, 420029 Kazan, Russia.
Beilstein J Nanotechnol. 2020 May 15;11:807-813. doi: 10.3762/bjnano.11.65. eCollection 2020.
Single-layer vanadium nitride (VN) and bilayer PdFe/VN and VN/PdFe thin-film heterostructures for possible spintronics applications were synthesized on (001)-oriented single-crystalline magnesium oxide (MgO) substrates utilizing a four-chamber ultrahigh vacuum deposition and analysis system. The VN layers were reactively magnetron sputtered from a metallic vanadium target in Ar/N plasma, while the Pd Fe layers were deposited by co-evaporation of metallic Pd and Fe pellets from calibrated effusion cells in a molecular beam epitaxy chamber. The VN stoichiometry and Pd Fe composition were controlled by X-ray photoelectron spectroscopy. In situ low-energy electron diffraction and ex situ X-ray diffraction show that the 30 nm thick single-layer VN as well as the double-layer VN(30 nm)/PdFe(12 nm) and PdFe(20 nm)/VN(30 nm) structures have grown cube-on-cube epitaxially. Electric resistance measurements demonstrate a metallic-type temperature dependence for the VN film with a small residual resistivity of 9 μΩ·cm at 10 K, indicating high purity and structural quality of the film. The transition to the superconducting state was observed at 7.7 K for the VN film, at 7.2 K for the PdFe/VN structure and at 6.1 K for the VN/PdFe structure with the critical temperature decreasing due to the proximity effect. Contrary to expectations, all transitions were very sharp with the width ranging from 25 mK for the VN film to 50 mK for the VN/PdFe structure. We propose epitaxial single-crystalline thin films of VN and heteroepitaxial Pd Fe /VN and VN/Pd Fe ( ≤ 0.08) structures grown on MgO(001) as the materials of a choice for the improvement of superconducting magnetic random access memory characteristics.
利用四腔超高真空沉积与分析系统，在（001）取向的单晶氧化镁（MgO）衬底上合成了用于可能的自旋电子学应用的单层氮化钒（VN）以及双层PdFe/VN和VN/PdFe薄膜异质结构。VN层是在Ar/N等离子体中从金属钒靶进行反应磁控溅射沉积的，而PdFe层是在分子束外延腔室中通过校准的蒸发源从金属Pd和Fe颗粒共蒸发沉积的。VN的化学计量比和PdFe的成分通过X射线光电子能谱进行控制。原位低能电子衍射和非原位X射线衍射表明，30nm厚的单层VN以及双层VN(30nm)/PdFe(12nm)和PdFe(20nm)/VN(30nm)结构均以立方对立方的方式外延生长。电阻测量表明，VN薄膜具有金属型温度依赖性，在10K时残余电阻率小，为9μΩ·cm，表明该薄膜具有高纯度和良好的结构质量。在7.7K时观察到VN薄膜转变为超导态，在7.2K时PdFe/VN结构转变为超导态，在6.1K时VN/PdFe结构转变为超导态，由于邻近效应，临界温度降低。与预期相反，所有转变都非常尖锐，宽度范围从VN薄膜的25mK到VN/PdFe结构的50mK。我们提出，在MgO(001)上生长的VN外延单晶薄膜以及异质外延PdFe/VN和VN/PdFe（≤0.08）结构是改善超导磁随机存取存储器特性的首选材料。
