The correlation between mechanical stress and magnetic anisotropy in ultrathin films

Abstract

The impact of stress-driven structural transitions and of film strain on the magnetic properties of nm ferromagnetic films is discussed. The stress-induced bending of film-substrate composites is analysed to derive information on film stress due to lattice mismatch or due to surfacestress effects. The magneto-elastic coupling in epitaxial films is determined directly from the magnetostrictive bending of the substrate. The combination of stress measurements with magnetic investigations by the magneto-optical Kerr effect (MOKE) reveals the modification of the magnetic anisotropy by film stress. Stress-strain relations are derived for various epitaxial orientations to facilitate the analysis of the substrate curvature. Biaxial film stress and magnetoelastic coupling coefficients are measured in epitaxial Fe films in situ on W single-crystal substrates. Tremendous film stress of more than 10 GPa is measured in pseudomorphic Fe layers, and the important role of film stress as a driving force for the formation of misfit distortions and for inducing changes of the growth mode in monolayer thin films is presented. The direct measurement of the magneto-elastic coupling in epitaxial films proves that the magnitude and sign of the magneto-elastic coupling deviate from the respective bulk value. Even a small film strain of order 0.1% is found to induce a significant change of the effective magneto-elastic coupling coefficient. This peculiar behaviour is ascribed to a second-order strain dependence of the magneto-elastic energy density, in contrast to the linear strain dependence that is valid for bulk samples. †

Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit

“…We find that for trilayers and thin bulk samples, Tc is consistent with the bulk value of 61 K. The relatively small decrease of Tc from bulk to few-layer and monolayer samples suggests that interlayer interactions do not dominate the ferromagnetic ordering in CrI3. Compared with metallic magnetic thin films whose 4 magnetic properties strongly depend on the underlying substrate 33,34 , the weak layer-dependent Tc also implies a negligible substrate effect on the ferromagnetic phenomena in atomically-thin CrI3. As such, exfoliated CrI3 of all thicknesses can be regarded as isolated single crystals.…”

Magnetization dynamics triggered by surface acoustic waves

“…depends on the mode of reversal, the method͑s͒ used to initiate the reversal, as well as the size, shape, and material properties of the ferromagnet, and has been investigated using short pulsed magnetic fields, 1 light pulses, 2 and thermal excitations 3 in pump-probe type experiments, with the fastest magnetization reversal occurring at a time scale of 30 ps. 3 The interplay between magnetization and strain, arising from the spin-orbit interaction, 4 is governed by the magnitude of the magnetostrictive coefficient. 5 In a recent experiment, 6 short light pulses excite picosecond acoustic waves, resulting in fast magnetization changes in a thin film of ͑Ga,Mn͒As.…”

Preparation of Existing and Novel Superconductors using a Spatial Composition Spread Approach

“…Therefore, SrLaAlO 4 (3.756 Å, -10%), SrTiO3 (3.905 Å, -6%), LaAlO 3 (3.821 Å, -8%) and SrLaGaO 4 (3.843 Å, -8%) substrates should all produce compressive strain, while MgO (a = 4.212 Å, +1%) should produce tensile strain in epitaxial films. It must be noted that film stresses of more than 10 GPa have been achieved in pseudomorphic Fe layers (Sander, 1999). Epitaxial films of the cuprate superconductors sometimes show enhanced T c perhaps because of the increase in J.…”