Ferromagnetic resonance in a magnetic trilayer with biquadratic exchange and unidirectional anisotropy

Stable states in a trilayer with a bilinear and biquadratic exchange interaction between ferromagnetically ordered layers and with strong unidirectional anisotropy are studied theoretically. It is shown that, in spin valves of this type, there may be a number of phase transitions of first or second order, and in the former case the width of the hysteresis loop is determined by biquadratic exchange. In the vicinity of the critical field the magnetic dynamics of the layer is shown to be approximately independent of that of other layers.