Modelling magnetic exchange springs in 1D, 2D, and 3D

1D models of magnetic multilayers, with alternating hard and soft layers, are extended to 2D and 3D, and presented within a common framework of nearest neighbour interactions. Using 2D calculations, it is shown that the properties of magnetic exchange springs can be changed significantly by patterning the hard pinning layers. But, in certain cases the bending field B B is not significantly altered, even when half the pinning layer is removed. 3D calculations are used to probe the effects of defects on the properties of magnetic exchange springs, using epitaxial DyFe 2 / YFe 2 superlattices as an example. It is shown that point defects such as Fe vacancies have little effect on the bending field transition. This is in marked contrast to the 1D model, where an Fe vacancy cuts the magnetic exchange spring into two. Finally, it is demonstrated that significant changes in the properties of magnetic exchange springs can be engineered, by placing rare-earth ions in the centre of the soft YFe 2 springs. A new phenomenon, exchange spring collapse , is predicted.