Study On Magnetic Properties Of Zn_1-xCr_xO Film By Co-sputtering Method

Nowadays, information is developing rapidly, people have more demands on the transmission, processing and storage of information. Spintronics makes the best use of both spin and charge of electrons to process and store information simultaneity, Diluted magnetic semiconductors have both magnetism and semiconductor performance, and they are the prospect materials in Spintronic devices. ZnO based semiconductor is the hotspot studying. Transition metal doped ZnO has already obtained room temperature ferromagnetism, but the origin and the nature of the ferromagnetism have confused and controversial. This text prepared Cr doped ZnO films by co-sputtering method, and tested the sample's structure, morphology, element composition and valence state, ferromagnetism etc. The text mainly studies the origin of the ferromagnetism of Cr doped ZnO films, and the influence of oxygen defects on the magnetization. Main research contents and results are as follows:(1) Studied the technology of Cr doped ZnO diluted magnetic semiconductor films prepared by magnetron co-sputtering method. All the Zn_1-xCr_xO samples showed room temperature ferromagnetism measured by PPMS, XRD,XPS and other testing methods show that Cr incorporates the ZnO crystal lattice as Cr³⁺, and forms Zn_1-xCr_xO diluted magnetic semiconductor, there is no second phase. The analysis indicates that the sample's magnetism is induced by ferromagnetic exchange between Cr ions.(2) Studied the sample's magnetization at external magnetic filed perpendicular and parallel to the film surface, respectively. The results show that parallel to the film surface is the easy magnetization axis,the sample shows anisotropic magnetization, this is another evidence for intrinsic nature of the ferromagnetism in Zn_1-xCr_xO films.(3) Studied the magnetism changes of the sample at different temperature. The sample shows both paramagnetism and ferromagnetism at 5K, and appears ferromagnetism at 100K, 340K. The saturated magnetization at 100K is bigger than the one at 340K.(4) Studied the influence of Cr doping concentration on the magnetism of the samples. The results show that the saturated magnetic moment per Cr is decrease with increasing Cr concentration, owing to the enhancement of antiferromagnetic coupling between Cr ions.(5) Studied the influence of O concentration on the magnetism of the samples. The Ms of the sample reaches at 0.503μB/Cr with Ar/O2 ratio at 9/1, and decreases at 0.409μB/Cr with Ar/O2 ratio at 9/6. This indicates that oxygen vacancy has significant influence on magnetism. The more oxygen vacancy quantity exists, the weaker the ferromagnetism is.(6) Studied the influence of annealing atmosphere on the magnetism of the samples. Vacuum annealing enhances the ferromagnetism of the films, but O2 annealing weakens it, because more oxygen vacancy exists in vacuum, but lack in oxygen, oxygen vacancy induced the ferromagnetism.