Effect of Au cap layer on the magnetic properties and the microstructure for FePt thin films

Abstract

We have investigated the effect of interfacial diffusion on the magnetic properties of Au∕Fe51Pt49 bilayer thin films. The samples were prepared in two stages. First, an ordered Fe51Pt49 continuous thin film was sputtered on a quartz substrate. Then an aurum cap layer was deposited onto the Fe51Pt49 film at room temperature, followed by a postannealing at 300–800°C to promote the interfacial diffusion. A high coercivity of 23.5kOe was achieved in the isotropic polycrystalline FePt-based film. Transmission electron micrographs indicate that the bilayer sample exhibits Ll0 ordered FePt grains with a diameter of about 20nm, which were partially isolated by Au phase. We consider that the isolation of FePtLl0 grains and the grain refining effect can be two contributory factors for the enhanced coercivity.

Microstructural Studies of L10-FePt Thin Films with High Coercivity Fabricated at Low Deposition Temperatures

“…With one layer of Ag layer inserted between FePt magnetic layers (structure II), the out-of-plane coercivity doubled with respect to that of FePt thin film without intermediate layer (structure I). With two ultrathin Ag layers inserted between FePt layers, the out-of-plane coercivity of the film with structure III dramatically increases to 32.5 kOe, which is much higher than the 24 kOe with Au [12] and 6 kOe with Cu additive layers. [13] The extrapolated anisotropy fields from hysteresis loops are estimated to be about 70 and 85 kOe for films with structures I and III, respectively.…”

“…However, there are some inevitable drawbacks: the magnetization of the FePt alloy is inevitably reduced, and the easy axis cannot be controlled in the direction normal to the film. Additional layers, such as Ag, [6] Au, [12] and Cu, [13] were reported to be effective in reducing the ordering temperature of L1 0 FePt alloys. A nonmagnetic top layer could enhance the coercivity of FePt films by promoting the disorder/order transformation of FePt thin films.…”

Microstructure and magnetic properties of Ag/FePt double layer films with different cooling processes

“…However, the formation of L1 0 -FePt film requires a heat treatment at a high temperature around 600 • C, which results in the grain growth [5,6]. Some investigations in lowering the ordering temperature and enhancing the coercivity of FePt film have been reported, such as doping a third element [7,8,9] and introducing an underlayer [10,11,12] and a capped layer [13] to the FePt film. Some techniques like applying a Multilayer structure [14,15], a magnetic soft underlayer [16,17] and molecular beam epitaxy [18,19] were used to improve the perpendicular anisotropy in FePt films.…”

Very high coercivities of top-layer diffusion Au/FePt thin films

“…The well-ordered FePt layer was firstly deposited on a quartz substrate at 800 1C to complete the L1 0 ordering transformation. A gold cap layer was then deposited on the FePt layer (Ordering parameter S $0.95) at room temperature, followed by a diffusion annealing at 800 1C for 1 h [5,7]. The Au cap layer has a constant thickness of 60 nm while the thickness of FePt layer is varied from 20 to 60 nm.…”

“…In the above cases, the ceramic matrixes play a role of obstacle for the ordering transformation of FePt, thus are detrimental to the magnetic properties of the film. To resolve the problem, a top-layer diffusion process was investigated [5][6][7]. A wellordered FePt continuous film was firstly deposited on a quartz substrate, and then annealed to form decoupled FePt grains.…”