Ultrahigh coercivity of granular CoCrPt-SiO2 thin films

Magnetic properties and microstructure of granular CoCrPt-SiO2 thin films with Cr underlayers have been investigated for potential applications in magnetic recording media. The coercivities exceeding 2500 Oe have been obtained in the as-deposited films with SiO2 varied from 8 to 16 vol %. Remarkable improvement in magnetic properties was achieved by postdeposition annealing in vacuum. The ultrahigh coercivity up to 5640 Oe was obtained in the lower SiO2 content film (CoCrPt)(96)(SiO2)(4) which was annealed at 580 degrees C for 10 min. The annealing did not induce significant grain growth. The average grain size varied from 10 to 20 nm, depending on SiO2 concentration. Grain isolation in magnetic layer was achieved by the segregated SiO2 and further enhanced by annealing. The ac demagnetized magnetic clusters, observed by magnetic force microscopy, became very fine after annealing. The peak value of delta M curves changed from positive to negative value, indicating a great reduction of intergrain magnetic exchange coupling after annealing. (C) 2000 American Institute of Physics. [S0021-8979(00)47108-2].