Engineering the magnetic properties of amorphous (Fe80Co20)80B20 with multilayers of variable anisotropy direction

Abstract

The main goal of this work is to generate a method to control the magnetic properties of magnetostrictive metals (anisotropy and coercive field) without affecting the total magnetostriction. Multilayers of amorphous (Fe80Co20)80B20 are sputtered changing alternatively the anisotropy direction of the successive layers. The hysteresis loops show how the anisotropy field can be controlled by playing with the thickness ratio of the layers. Additionally, a clear decrease of the coercive field when the anisotropy direction rotates 90° from layer to layer is observed. This effect seems to have its origin in the mechanical energy accumulated in each layer.

Origin of in-plane uniaxial magnetic anisotropy in CoFeB amorphous ferromagnetic thin films

“…The change in UMA under macroscopic stress, σ, is ∆K vol U (σ) = λσ: thus under applied macroscopic strain λ = ∆K vol U (ǫ)/Y ǫ. Taking Y = 162 GPa 26 , we find λ ≈ 3.5 × 10 −5 : consistent with what may be anticipated for (CoFe) 80 B 20 alloy films9,13 . Thus, as K vol,SM /2Y ǫ 2 ∼ 3 × 10 4 erg/cm 3 , one would expect solely elastic SM in (CoFe) 80 B 20 may produce UMA with H K ∼ 50 Oe.…”

“…Thus, despite the absence of an applied magnetic field during film deposition, we find a significantly enhanced UMA, with H K ∼ 150 Oe (K eff U ∼ 8 × 10 4 erg/cm 3 ) in amorphous CoFeB on GaAs(001). UMA of such strength has previously been observed in amorphous CoFeB films deposited at obliqueincidence 13 , confirming that the UMA should be related in some way to anisotropy in the film microstructure 18 . However, our films were deposited at normal incidence.…”

“…Finally, we comment on why the volume UMA due to oblique deposition or interface interaction dominates over that due to applied magnetic field during deposition 8,13,17 . During the initial stages of growth, a magnetic field alone may induce BOA by aligning the magnetic moments µ, and hence microstructure, of isolated superparamagnetic coordination clusters, typically with ∼ 10 atoms 21 and hence µ ∼ 20 µ B .…”

“…Details of the fabrication of such devices using (Ga,Mn)As epilayers may be found in refer- First we present the experimental evidence to establish that the UMA is a volume contribution and that it is seeded by the interface. Inducing in-plane volume UMA during film deposition requires azimuthal symmetry to be broken: typically achieved by applying an in-plane magnetic field 12 , or using a deposition geometry whereby the atomic flux impinges at an angle to the substrate normal 13 . In the absence of such symmetry breaking, random local magnetic anisotropy results, due to short-range ordering in the amorphous FM.…”

Assessment of Layer Thickness and Interface Quality in CoP Electrodeposited Multilayers

“…However, considering the close relationship between magnetostriction and magnetization processes, it can be also used as a tool to have a deep insight into the magnetic properties of magnetic materials. In this sense, we have carried out magnetostriction measurements in a homemade experimental setup based on the optical method presented by Tam and Schroeder. , This system has been previously used for measuring magnetostriction in crystalline and amorphous materials as well as in amorphous CoP multilayers, similar to the one reported in this work. For measuring, the magnetic material is deposited on a nonmagnetic substrate, which is clamped by one end forming a cantilever.…”