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Ion implantation followed by thermal processing has been used to synthesize nanoparticles of cobalt–platinum (Co–Pt) alloys in single-crystal Al2O3. Several phases, including CoPt in the L10 structure, Co3Pt, and CoPt3 that has the L12 structure, are selectively formed by varying the atomic ratio of implanted Co and Pt. These alloys are crystallographically oriented with respect to the host Al2O3 matrix, exhibiting multiple distinct orientations. Rutherford backscattering and X-ray diffraction have been used to study the influence of the processing conditions, including temperature and dose, on the formation of the alloys. The degree of chemical ordering in the L10 and L12 phases is not high and it is not improved significantly with long annealing times. Magnetization studies have been conducted using a SQUID magnetometer. Coercivities as high as 14.2 kOe (9.7 kOe) at 5 K with the field normal (parallel) to the surface have been measured, and they remain significant at room temperature and above. The coercivity is a function of the Pt fraction in the alloy. |
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