Preparation And Magnetic Properties Of Ca_1-xLa_xB₆ Thin Films Deposited By Magnetron Sputtering

CaB₆ has excellent comprehensive properties, also has an important role in industry and scientific research. Report of high temperature weak ferromagnetism of La doped CaB6 lead to a broad prospect in the field of electron spin components. Films usually have special physical and chemical properties. Properties of the film closely related to the film morphology, structure and composition. The aim of this paper was to build correlations between different sputtering parameters, different La doping concentrations and microstructures, surface morphology, chemical compositions, molecular structures and physical properties. The growth mechanism of Ca1-xLaxB6 films was established. In addition, particular attentions have been given to the origin of special magnetism and the variation tendency in this paper.Effects of different sputtering parameters on CaB6 films growth were studied by XRD, FESEM, AFM and RAMAN. When the argon pressure was 1.5 Pa, sputtering power was 90 W, bias voltage was-100 V, high crystallization and （100） texture appeared in the films. Surface of the film was formed by the （100） orientated columnar crystalline which tipped by fourfold symmetric （110） pyramid-shaped facets. The crystallization degree, grain size and surface roughness increased with the sputtering time. They increased at first and then decreased with the increasing of argon pressure, sputtering power and bias voltage. The structure and surface morphology were co-determined by shadowing effects, different surface mobilities of adatoms on different crystal planes and kinetic factors.Effects of La doping concentrations on Ca1-xLaxB6 （x=0/0.01/0.02/0.03） films morphology, chemical compositions, molecular structures and physical properties were investigated through changing La doping concentrations. Grain growth was much enhanced by La doping. The growth rate and grain size of La doped Ca1-xLaxB6 films were clearly higher than that in undoped films. The chemical composition of Ca1-xLaxB6（x=0/0.01/0.02/0.03） films was detected by XPS. La concentrations were closed to the stoichiometric values, and B atoms were insufficient in the films. Both EDS and XPS studies confirmed that no other ferromagnetic impurities （eg. Fe） existed in Ca1-xLaxB6 films. Doped La atoms lead to the decrease of the bonding energy between inter-octahedral B-B bonds and the tilting or rotating of the B6 octahedron.The saturation magnetization of Ca1-xLaxB6 films increased in the order of CaB6, Ca0.97La0.03B6, Ca0.99La0.01B6, Ca0.98La0.02B6. The largest moment was 84.54 emu/cm3 appeared in Ca0.98La0.02B6 films. There was a clear decrease of the saturation magnetization （Ms） with the increase of sputtering time. The values of Ms sharply decreased with the sputtering time increasing from 1 min to 30 min. The magnetism is an intrinsic feature of the Ca1-xLaxB6 films, while not originate from other elements.