A novel type of exchange spring media is proposed for magnetic recording systems consisting of a hard/soft bilayer. Finite element micromagnetic simulations show that the reversal modes induced by the external write field are significantly different from the thermally activated switching processes. Thus, the bilayers can be optimized in order to achieve a high thermal stability without increase of coercive field. In grains with identical size and coercivity an optimized bilayer reaches an energy barrier exceeding those of optimized single phase media by more than a factor of two. Additionally the lower angular dependence of coercivity of exchange spring media will improve the signal to noise ratio.

A mechanism for exchange bias and training for antiferromagnet/ferromagnet bilayers with fully compensated interfaces is proposed. In this model, the bias shift and coercivity are controlled by domain wall formation between exchange coupled grains in the antiferromagnet. A finite element micromagnetic calculation is used to show that a weak exchange interaction between randomly oriented antiferromagnetic grains and spin flop coupling at a perfectly compensated interface are sufficient to create shifted hysteresis loops characteristic of exchange bias. Unlike previous partial wall models, the energy associated with the unidirectional anisotropy is stored in lateral domain walls located between antiferromagnetic grains. We also show that the mechanism leads naturally to a training effect during magnetization loop cycling.

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Micromagnetic calculations at nonzero temperatures depend on the computational cell size. This paper shows that the spontaneous magnetization MS of exchange-coupled moments has to be scaled by a Bloch-like law, which is similar to the well-known temperature dependence of MS. Using this scaling law, nonatomistic Metropolis Monte Carlo and stochastic Landau–Lifshitz–Gilbert simulations are performed in an external field of 0.1T. The error of the equilibrium magnetization at a temperature of T∕TC=0.38 and a cell size of 1.5nm is then 0.9% as compared with atomistic calculations. In contrast, a cell size-independent MS leads to an overestimation of the temperature of 3.2%.

Detailed studies of the structure of magnetic nanoclusters are crucial for understanding their magnetic properties. We have investigated the structure of Co x Ag 1−x nanoparticles by means of molecular dynamics simulations utilizing the embedded atom method. Starting from a completely random distribution of Co and Ag atoms, the clusters were heated up to 1300 K and subsequently cooled down. The size of the resulting particles was 2.8 nm ͑864 atoms͒. A clear segregation of the Ag atoms on the surface of the Co core was obtained.