Magnetostrictive hysteresis of TbCo∕CoFe multilayers and magnetic domains

Abstract

Magnetic and magnetostrictive hysteresis loops of TbCo∕CoFe multilayers under field applied along the hard magnetization axis are studied using vectorial magnetization measurements, optical deflectometry, and magneto-optical Kerr microscopy. Even a very small angle misalignment between hard axis and magnetic field direction is shown to drastically change the shape of magnetization and magnetostrictive torsion hysteresis loops. Two kinds of magnetic domains are revealed during the magnetization: big regions with opposite rotation of spontaneous magnetization vector and spontaneous magnetic domains which appear in a narrow field interval and provide an inversion of this rotation. We show that the details of the hysteresis loops of our exchange-coupled films can be described using the classical model of homogeneous magnetization rotation of single uniaxial films and the configuration of observed domains. The understanding of these features is crucial for applications (for microelectromechanical systems or microactuators) which benefit from the greatly enhanced sensitivity near the point of magnetic saturation at the transverse applied field.