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 MEMS or microactuators) which benefit from the greatly enhanced sensitivity near the point of magnetic saturation at the transverse applied field.

Direct and inverse measurement of thin films magnetostriction

“…As observed with VSM similarly to our previous study 23 the unstressed sample has a uniaxial anisotropy: rectangular magnetization along the sample length shows the easy axis and slanted magnetization along the sample width (hard axis magnetization) provides the initial anisotropy value (see Fig. 3(a)) For positive curvatures (left column), the large axis hysteresis loop shape does not vary, keeping the rectangular shape characteristic for the easy axis magnetization, whereas the short axis hysteresis loop is getting more and more slanted when curvature increases.…”

“…The direct measurements were realized using cantilever deflectometry technique. Details of the sample preparation and of the cantilever measurements can be found in 23 . For the inverse measurement we have studied local magnetization curves of bent sample using the magnetooptical Kerr effect (MOKE) as shown in figure 2.…”

Model for magnetostrictive performance in soft/hard coupled bilayers

“…Numerical modeling of micromachined flexible magnetostrictive thin film actuator has been developed based on the finite-element method [11]. Classical model of homogeneous magnetization rotation of single uniaxial films was established in order to understand the features of magnetic and magnetostrictive hysteresis loops of TbCo/CoFe multilayers under magnetic field along hard magnetization axis [12]. The key issues in the soft/hard exchange coupled bilayers are the nature of the coupling and the spin structures in the hard layer for its huge magnetic anisotropy [13][14][15].…”

Magnetostrictive properties of amorphous SmCo thin films with imprinted anisotropy

“…The parameter used to describe the size of the magnetostriction in thin films is the magnetoelastic coupling coefficient, which is defined as the difference of the magnetic field induced stress for the field applied parallel and perpendicular to the easy axis, or [24,25] …”

“…where Y s , ν s , and t s are the Young modulus, Poisson ratio, and thickness of the substrate and t f is the film thickness [24][25][26]. Young's modulus and Poisson's ratio in silicon are dependent on the orientation of the stress relative to the crystal axes of the sample.…”