Uniaxial magnetic anisotropy of tetragonal FeCoV and FeCoVC films

Abstract

The tetragonal crystalline structure and magnetic properties of MgO/Rh/(Fe1−xCox)0.9V0.1 and MgO/Rh/(Fe1−xCox)0.9V0.05C0.05 films (0.4 x 0.7, thickness t = 2–50 nm) were studied. For both the systems, the films with t = 5 nm showed a tetragonal distortion (c/a) of ~1.15 at x = 0.6. Furthermore, in the case of (Fe1−xCox)0.9V0.05C0.05, the films showed a c/a value of ~1.06 even at t = 50 nm. The magnetic anisotropy induced by the tetragonal distortion of films became 1.4 × 107 erg cm−3 for (Fe1−xCox)0.9V0.1 (t = 5 nm) and (Fe1−xCox)0.9V0.05C0.05 (t = 5 nm) films. We also investigated the tetragonal distortion stability of the films using their enthalpy of formation (ΔH) values obtained from density functional theory calculations.

Stabilisation of tetragonal FeCo structure with high magnetic anisotropy by the addition of V and N elements

“…Rh was selected as the buffer layer material because it exhibited the lattice mismatch ( a FeCo − a Rh /)/ a FeCo ≈ 0.05–0.07 across the bcc–fcc FeCo structures, which was considered suitable for epitaxial growth. According to the results of our previous studies 27 , the addition of 10 at.% V to FeCo films produced the maximum value of K u .…”

“…In our previous study 27 , we focused on the use of vanadium as the third additive element because of its ability to form a bcc solid solution around Fe 50 Co 50 clusters, which was subsequently transformed into the fcc phase with an increase in the V content. A stabilisation of the bct phase was expected to occur at the boundary between the bcc and fcc phases.…”

“…Five possible factors can be considered: (1) pinning the domain walls at non-magnetic precipitates or at the B 2 anti-phase boundaries, (2) shape anisotropy of the bcc phase, (3) stress-induced anisotropy, (4) magnetic anisotropy of martensitic needles, and (5) magnetic anisotropy of B 2 ordered bct precipitates. Previously 27 , it was reported that the semi-hard magnetic properties of vicalloys could be mainly attributed to the fifth factor (the presence of tetragonally distorted precipitates or clusters during the bcc−bct−fcc transformation) and that they could be potentially improved by the formation of the bct phase. Although V addition was expected to stabilise the bct phase, the examined FeCoV and FeCoVC films were unable to achieve c/a = 1.2 27 .…”

“…Previously 27 , it was reported that the semi-hard magnetic properties of vicalloys could be mainly attributed to the fifth factor (the presence of tetragonally distorted precipitates or clusters during the bcc−bct−fcc transformation) and that they could be potentially improved by the formation of the bct phase. Although V addition was expected to stabilise the bct phase, the examined FeCoV and FeCoVC films were unable to achieve c/a = 1.2 27 . In this study, the effect of the VN addition to FeCo films on their tetragonal deformation and magnetic properties was investigated.…”

Investigation of the body-centred tetragonal structure of Fe–Co–V–N Bulk foils using the rolling and ammonia-gas-nitriding method

“…Before bulk-forming (using method (ii)), FeCo films with added α (such as Al, Ti, and V) and β (such as C and N) elements were epitaxially grown on a Rh buffer layer. In previous studies, this resulted in the successful formation of a bct structure 7,[9][10][11][12][13] . Further, a combination of α = V and β = N proved to be the most effective in forming a bct structure with c/a ≈ 1.2 in thin (t ≤ 5 nm) and thick (t = 100 nm) films, and a large K u of 1 MJ/m 3 was obtained 9,[12][13][14] .…”