Mohanty P, Chowdhury S, Choudhary R J, Gome A, Reddy V R, Umapathy G R, Ojha S, Carleschi E, Doyle B P, Prinsloo A R E, Sheppard C J
Cr Research Group, Department of Physics, University of Johannesburg, Johannesburg, PO Box 524, Auckland Park, South Africa.
Nanotechnology. 2020 Jul 10;31(28):285708. doi: 10.1088/1361-6528/ab83b4. Epub 2020 Mar 26.
Cubic spinel CoCrO has recently attained attention due to its multiferroic properties. However, the Co site substitution effect on the structural and magnetic properties has rarely been studied in thin film form. In this work, the structural and magnetic properties of Co Ni CrO (x= 0, 0.5) epitaxial thin films deposited on MgAlO (100) and MgO (100) substrates to manipulate the nature of strain in the films using pulsed laser deposition (PLD) technique are presented. The epitaxial nature of the films was manifested through x-ray diffraction (XRD), reciprocal space mapping (RSM) and Rutherford backscattering spectrometry (RBS) measurements. Raman measurements revealed a disappearance of characteristic A and F modes of the CoCrO with increase in the Ni content. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) studies show a modification of the surface morphology upon Ni substitution. Magnetic measurements disclose that the ferrimagnetic Curie temperature (T ) of the CoCrO in thin film grown on MgAlO (100) and MgO (100) substrates were found to be 100.6 ± 0.5 K and 93.8 ± 0.2 K, respectively. With Ni substitution the T values were found to be enhanced to 104.5 ± 0.4 K for MgAlO (100) and 108.5 ± 0.6 K for MgO (100) substrates. X-ray photoelectron spectroscopy (XPS) suggests Cr oxidation states in the films, while Co ions are present in a mixed Co/Co oxidation state. The substitution of Ni at Co site significantly modifies the line shape of the core level as well as the valence band. Ni ions are also found to be in a mixed 2+/3+ oxidation state. O 1s core level display asymmetry related to possible defects like oxygen vacancies in the films.
立方尖晶石CoCrO最近因其多铁性特性而受到关注。然而，钴位点取代对结构和磁性的影响在薄膜形式下很少被研究。在这项工作中，展示了使用脉冲激光沉积（PLD）技术在MgAlO(100)和MgO(100)衬底上沉积的CoNiCrO（x = 0, 0.5）外延薄膜的结构和磁性，以控制薄膜中的应变性质。通过X射线衍射（XRD）、倒易空间映射（RSM）和卢瑟福背散射光谱（RBS）测量证明了薄膜的外延性质。拉曼测量表明，随着镍含量的增加，CoCrO的特征A和F模式消失。原子力显微镜（AFM）和场发射扫描电子显微镜（FE-SEM）研究表明，镍取代后表面形貌发生了改变。磁性测量表明，在MgAlO(100)和MgO(100)衬底上生长的薄膜中，CoCrO的亚铁磁性居里温度（T）分别为100.6±0.5 K和93.8±0.2 K。随着镍的取代，MgAlO(100)衬底的T值提高到104.5±0.4 K，MgO(100)衬底的T值提高到108.5±0.6 K。X射线光电子能谱（XPS）表明了薄膜中铬的氧化态，而钴离子以Co/Co混合氧化态存在。钴位点处镍取代显著改变了核心能级以及价带的线形。还发现镍离子处于2+/3+混合氧化态。O 1s核心能级显示出与薄膜中可能的缺陷（如氧空位）相关的不对称性。
