We present the results of investigation of spin-tunnel magnetoresistive FeNi-SiC-FeNi nanogeterostructures with various combinations of composition and layer thickness. The samples were grown on glassceramic substrates by magnetron sputtering with alternative sputtering of polycrystalline FeNi and SiC targets. Magnetic and magnetooptical (MO) properties of nanostructures possessing symmetric and asymmetric arrangement of semiconductor layers relative to the ferromagnetic metal ones were studied by induction method and by transversal Kerr effect (TKE).

An unusual dependence of reversal magnetic field on the AC magnetic field amplitude was found in symmetrical structures: it has a N-like character with minima of at some values of . The asymmetrical FeNi-SiC-FeNi nanostructures with various revealed existence of a shift of hysteresis loops that depends on the SiC layer thickness. Existence of such shift testifies that there exists an interaction between the semiconductor layer and the ferromagnetic films. In symmetrical nanostructures such shifts were not observed.

The MO studies have demonstrated that in the samples with thin ferromagnetic and semiconductor layers the TKE magnitude in maximums of the effect (in the energy range and eV) is, as a rule, greater than in nanostructures with thicker ferromagnetic layers and greater than in the bulk permalloy samples. In magnetic fields above 1 kOe the TKE orientation dependence reveal extremums at two perpendicular directions of magnetization, so the existence of a uniaxial anisotropy could be assumed. However, in the field range below 150 Oe there were observed deformations of curves and even inversions of maximum and minimum values of the TKE corresponding to the hard and easy magnetization axes. In the range below 150 Oe the curves of the TKE magnetic field dependence demonstrate a number of anomalies, which deform the usual smooth shape of magnetization curves in such a way that there appear multiple crossings of curves corresponding to these directions.

We propose a number of possible explanations of the observed behavior of magnetic and magnetooptical properties. The most probable seems to be the idea that magnetization vectors within ferromagnetic layers are antiparallel (or oriented at some angle to each other). In this case there appears an opportunity to use small external magnetic field to control the magnitude of ferromagnetic layers interaction through semiconductor barrier separating them.

The work was supported by the Russian Foundation for Basic Research (grants 01-02-16788, 01-02-16403) and National Program Physics of Solid State Nanostructures (grant 97-1050).