Study of ferro-antiferromagnetic transition in [001]-oriented L1 FePt1−xRhx film

Magnetic properties of [001]-oriented L10 FePt1−xRhx films (tFePtRh=6.12 nm) with Rh composition (x) of 0≤x≤0.40 were studied, and the magnetic phase in a composition-temperature plane was investigated. At room temperature, the films with 0≤x≤0.32 were in a ferromagnetic (FM) phase with a coercivity of several kilo-oersteds, and the films with 0.34≤x≤0.40 were in an antiferromagnetic (AF) phase. At x=0.32, which is close to the critical composition of the FM-AF transition at room temperature, the uniaxial magnetocrystalline anisotropy (Ku) was about 1.7×107 erg/cm3. A bit patterning process using the discontinuous FM-AF transition was studied. First, microfabricated FePt square films (1.7 nm thick) were prepared on the AF FePt0.64Rh0.36 film (6.7 nm thick). Second, those square films and the FePt0.64Rh0.36 film were mixed by annealing. The Fe and Pt atoms were thermally diffused into the FePt0.64Rh0.36 film locally, and the composition of the diffused areas changed to FM FePt0.72Rh0.28. A magnetic force microscopy study suggested that only the diffused areas changed from AF to FM phase. A minimum FM dot size of 300×300 nm2 was realized, and the FM dots were multidomain structures.