As is well known, the processes of magnetization reversal in traditional bulk ferromagnetic materials cannot be described without taking into account the influence of crystal lattice defects. It has been shown that the characterisics of magnetization curves of real crystals are determined by the minimization of both magnetostatic energy and magnetoelastic energy. Significant contributions to the latter energy are the relativistic and exchange interactions between magnetic spins caused by spatially inhomogeneous internal stresses. Dislocations are one of the most important sources of internal stresses, since each of them produces a slowly-decreasing long-range stress field. Consequently, theories are being developed in ferromagnets[1,2] to explain the effect of dislocations on the processes of magnetization rotation and of domain-wall motion. Direct experimental study of the influence of individual dislocations on these processes has shown [3-5] that the dislocation induces an inhomogeneous distribution of the magnetization vectors around it, affects the rotation of these vectors under the action of an external magnetic field, determines the kinetics of spin reorientation phase transformations, and acts as a pinning center for domain wall motion.
Until now, the influence of dislocations (and other crystal defects) on the properties of modern magnetic nanostructured materials has not been studied. In exchange-bias films, for example, most attention in the past has been focussed on interface roughness [6] effects in order to explain the difference between theory and experiment of the exchange anisotropy field, HE. In the present report, we show experimental data that crystal lattice defects and, in particular, dislocations dramatically influence the magnetization reversal processes in thin NiO/NiFe bilayers.