In-plane uniaxial magnetic anisotropy induced by anisotropic strain relaxation in high lattice-mismatched Dy/Sc superlattices

Abstract

We report on the magnetic and structural characterization of high lattice-mismatched [Dy 2nm /Sc t Sc ] superlattices, with variable Sc thickness t Sc = 2-6 nm. We find that the characteristic in-plane effective hexagonal magnetic anisotropy K 6,ef 6 reverses sign and undergoes a dramatic reduction, attaining values of ≈13-24 kJm −3 , when compared to K 6 6 = −0.76 MJm −3 in bulk Dy. As a result, the basal plane magnetic anisotropy is dominated by a uniaxial magnetic anisotropy (UMA) unfound in bulk Dy, which amounts to ≈175-142 kJm −3 . We attribute the large downsizing in K 6,ef 6 to the compression epitaxial strain, which generates a competing sixfold magnetoelastic (MEL) contribution to the magnetocrystalline (strain-free) magnetic anisotropy. Our study proves that the in-plane UMA is caused by the coupling between a giant symmetry-breaking MEL constant M 2 γ,2 ≈ 1 GPa and a morphic orthorhombiclike strain ε γ,1 ≈ 10 −4 , whose origin resides on the arising of an in-plane anisotropic strain relaxation process of the pseudoepitaxial registry between the nonmagnetic bottom layers in the superstructure. This investigation shows a broader perspective on the crucial role played by epitaxial strains at engineering the magnetic anisotropy in multilayers.

Spin-flop transition driven by competing magnetoelastic anisotropy terms in a spin-spiral antiferromagnet

“…The existence of a fully symmetric sixfold MEL coefficient λ 66 , which gives rise to the sixfold modulation of the α strains ε α1 (isotropic volume expansion) and ε α2 (tetragonal distortion of the hexagonal cell), originates a 12-fold MEL-induced magnetic anisotropy energy (MAE) constant K 12 12 as experimentally confirmed in bulk holmium [22]. The existence of λ 66 is associated with the appearance of six-fold MEL constants, which may not be solely restricted to the Ho metal [23]. More importantly, λ 66 , and by extent K 12 12 , exhibits a visible nonmonotonic dependence on temperature [22].…”

“…(11), replicates a change of sign in K 6,eff 6 as H is swept in the [Ho 85 /Lu 15 ] 50 superlattice (SL), in which the SFT was first observed [21], the first aspect we must consider is the influence that the finite size [50] of the Ho layers has upon the MEL constants. Thus, as an earlier study [47] has shown, the development of typical epitaxial strains in multilayered rare earth based systems originated a negligible alteration, if any at all, in the γ -MEL constants, however, the α-MEL ones experienced an appreciable strain-induced modification, which is in a general case modelled as follows [23]:…”

Universal scaling of the magnetic anisotropy in two-dimensional rare-earth layers

“…Both SLs were grown by a molecular beam epitaxy technique in a Balzers UMS630 facility, with a base pressure of better than 2 × 10 −10 mbar and deposited onto epi-polished (1120)-oriented Al 2 O 3 substrates, following well-established growth techniques [35,36]. This procedure ensures that the Dy, Sc, Ho, and Lu metallic species, which all crystallize in the hexagonal-closed-packed (hcp) structure [30], grow with the c direction of the hcp lattice structure normal to the deposition plane [35,36], forming high-quality single crystals [37,38].Magnetic torque measurements were carried out in a vector vibrating sample magnetometer [39]. Data recorded by this apparatus have significantly contributed to a better understanding of the influence that strain-induced magnetoelastic (MEL) terms [29,38,40] have upon the MAE in nanosystems and to demonstrate the anisotropy of the magnetization…”

“…This procedure ensures that the Dy, Sc, Ho, and Lu metallic species, which all crystallize in the hexagonal-closed-packed (hcp) structure [30], grow with the c direction of the hcp lattice structure normal to the deposition plane [35,36], forming high-quality single crystals [37,38].…”

“…Both SLs were grown by a molecular beam epitaxy technique in a Balzers UMS630 facility, with a base pressure of better than 2 × 10 −10 mbar and deposited onto epi-polished (1120)-oriented Al 2 O 3 substrates, following well-established growth techniques [35,36]. This procedure ensures that the Dy, Sc, Ho, and Lu metallic species, which all crystallize in the hexagonal-closed-packed (hcp) structure [30], grow with the c direction of the hcp lattice structure normal to the deposition plane [35,36], forming high-quality single crystals [37,38].…”