Coupling of the magnetic layers and electron spin polarization in four-layer structures of amplitude and nonmagnetic semiconductors

Abstract

The electron energy spectrum, the energy Em of the exchange coupling between magnetic layers, and the relative polarization β of the electron spins in semiconductor structures with two ferromagnetic barriers and nonmagnetic layers acting as potential wells for electrons are considered. For the example of EuS/PbS(001) structures it is shown that in the case of Fermi statistics Em is a sign-varying oscillatory function of the width a of the potential well between barriers, and with increasing electron density n0 in the wells and increasing thickness d of the nonmagnetic sublayers between the barrier and substrate, the extrema of Em are shifted to smaller a and their amplitudes rapidly increase. As the temperature is lowered from the Curie point, the energy Em, depending on a, n0, and d, can increase (in modulus) monotonically or nonmonotonically, change sign from positive to negative, or change sign twice. The polarization β decreases with increasing a, n0, and d, undergoing sharp jumps when Em changes sign. For Boltzmann statistics only a ferromagnetic orientation of the barrier magnetizations (Em<0) is possible.