The Structure,Magnetic Properties And Intergranular Interaction Of CoPt-C Nanogranular Films And The Structure And Magnetic Properties Of CoPt₃ Alloy Films

I . The granular structure was obtained by depositing CoPt/C in a multilayers form (consisting of 80 repetitions) and subsequently annealed the samples at 700癈 Ih to form the nanoparticles. The films were prepared by magnetron sputtering deposition from three targets Co, Pt and C. The base pressure of the chamber was 5*10"5Pa and high purity Ar (99.9999%) was used for deposition at ambient temperature with a pressure of O.SPa. The substrates used were Si(lOO) and a 300 A C buffer layer was used to ensure similarity of growth conditions between samples sputtered on different kinds of substrates. Three kinds of samples with different stoichiometry were made, which are CoaoPteg /C, Co3oPt37 /C and Co2APtxA /C alloy films. XRD spectra were collected with a SIEMENS D600 power diffractometer using Cu K radiation. Magnetic hysteresis loops were measured with AGM. The microstructure was examined with a Philips CM 20 and a Jeol JEM 2010 FX TEM transmission electron microscope. The composition of the alloy was evaluated using NORNN EDXIn this paper, we have investigated the structure, magnetic properties and intergranular interaction of CoPt/C.1. (Ill) texture of CoiPti and/or CoiPts has been observed in annealed sample I [CosoPtegSA/CxAJgo (x=0-12 A). CoPt particles are segregated by nonmagnetic C. With the increasing of C thickness, the CoPt grains sizes are reduced.2. Magnetic properties:(1) Easy axes of annealed sample I [CosoPtegS A /CxAjgo (x=0-12 A) lie in plane. With the increasing C thickness from 0 A to 4 A, the coercivities are greatly improved from 1540 Oe to 5400 Oe. The coercivities are reduced when C thickness is above 4 A. As a function of C thickness, demagnetization remanence curves firstly show smooth, then the distinct shoulders are observed, finally the curves trend to smooth. The trend of Hs are similar to that of coercivities. Mr/Ms are kept above 0.9 in all samples I .(2) The coercivities in annealed samples II [Co3oPt3v4 A /CxA]80 (x=0-6A) firstly appear to increase, then decrease with the C thickness. But the coercivities improved of samples II are smaller than those of samples I .The demagnetization remanence curves undergo a whole process from smooth to shoulders then smooth again. Mr/Ms remains between 0.8 and 0.9 in samples II .The changing trends of Hs are similar to that of coercivities of samplesII.(3) The coercivity of annealed [Co30Pt698 A /C4 A]go is the largest among annealed samplesIII [PtxACo2 A /C4 A]80,under the fixed C and Co thickness.3. According to demagnetization remanence curves, we investigated the intergranular interactions of annealed [CosoPtegS A /C4 A]8o using 5mand Henkel curves. When Ha(applied field) is smaller than the coercivity, the negative contributions are completely suppressed by positive-exchange-type interactions. However, a small amount of negative magnetostatic part superimposes over positive-exchange-type interactions when Ha is above Hc.II. The CoPts alloy films were sputtered deposited by dc magnetron sputtering on glass. The background Pressure was maintained below 5*10~7Torr and Ar was used as the sputtering gas. The samples were deposited at 2.0Pa , which were the Co chips mounted on a 6 in. Pt target. Heat treatment of the samples was carried out at temperature ranging from 300 ℃ to 600℃ in vacuum of 10"3Pa. The structure of the alloy film was investigated by X-ray diffraction (XRD) analysis and the magnetic properties were measured by a Alternating Gradient Magnetometer (AGM). The surfaces of CoPts alloy films were observed by atomic force microscopy (AFM)and the domain structure of samples has been investigated by magnetic force microscopy(MFM).The structure and magnetic properties were studied in this thesis. The major results obtained are summarized as follows:1. A perfect (111) texture is observed in both the as-deposited and the annealed films. The face-centered cubic (FCC) crystal orientation is improved with Ta.2. The coercivity slightly increases below 500℃ and decreases...