REVERSAL OF MAGNETIZATION OF AGGREGATES OF MAGNETIC PARTICLES BY A VORTICITY FIELD AND USE OF TOROIDNESS FOR RECORDING INFORMATION

Reversal of magnetization of aggregates of fine magnetic particles frozen in a polymer solid matrix is considered. The simple theory is constructed where only two vector parameters are used to describe the magnetic state of the aggregate: its magnetic dipole and toroid moments. The numerical simulation is also used for this purpose which is based on the micromagnetic methods modified for our case. The great number of the small aggregates of different space forms are considered and it is shown, that in the absence of of an external magnetic field in the minimum energy state the distribution of the particles magnetic moments has a vortex configuration which can be described by the toroid vector moments. When the vortex field is applied (with the vortex G = rot H) the toroid hysteresis takes place. The 'coercive force' G(c) is evaluated and its dependence on the additional field H is studied. The application of a toroid hysteresis to a new kind of magnetic recording ('toroid recording') is discussed in detail. In this case the recording of information can be done by the simultaneous action of the vortex and the uniform magnetic fields. The reading of the record can be done by the registration of the electric field which is induced by the oscillating toroid moments.