Out-of-plane magnetic patterning on austenitic stainless steels using plasma nitriding

Abstract

A correlation between the grain orientation and the out-of-plane magnetic properties of nitrogen-enriched polycrystalline austenitic stainless steel surface is performed. Due to the competition between the magnetocrystalline anisotropy, the exchange and dipolar interactions, and the residual stresses induced by nitriding, the resulting effective magnetic easy-axis can lay along unusual directions. It is also demonstrated that, by choosing an appropriate stainless steel texturing, arrays of ferromagnetic structures with out-of-plane magnetization, embedded in a paramagnetic matrix, can be produced by local plasma nitriding through shadow masks.

Magnetic layer formation on plasma nitrided CoCrMo alloy

“…This variation was explained by the non-uniform N contents and different amounts of lattice expansion in the differently oriented grains. A more recent plasma nitriding study of 316L polycrystalline austenitic stainless steel (via MFM and MOKE analyses) verified that the magnetic response of nitrogen-enriched grains is correlated to their crystallographic orientation [12].…”

“…More recently, the magnetic character of the γ N phase has been studied by magnetic force microscopy (MFM) [9][10][11][12]. According to these MFM analyses, the ferromagnetism in the γ N layers on austenitic stainless steels is revealed via the observation of stripe domain structures.…”

“…defects, and local deformation. Another plasma nitriding study of 316L SS via MOKE and MFM [12], at a more fundamental level, attributes different domain morphologies (variation in the size and form) mainly to the balance between exchange, anisotropy, and dipolar energies. The magnetic behavior of the γ N layers on the CoCrMo substrate material was also investigated by magneto-optic Kerr effect (MOKE).…”

“…The ferromagnetic γ N is attributed to an fcc structure with N in octahedral interstitial sites but with larger N contents than the paramagnetic γ N phase [4]. Recent research [9][10][11][12] involving MFM imaging of the N ion beam modified austenitic SS surfaces show that the ferromagnetism in the γ N phase is also revealed through the appearance of the striped domain structures with out-of-plane magnetization. Magnetic domains with in-plane magnetization have also been observed by MFM in nitrided austenitic stainless steels [12,13].…”

“…Recent research [9][10][11][12] involving MFM imaging of the N ion beam modified austenitic SS surfaces show that the ferromagnetism in the γ N phase is also revealed through the appearance of the striped domain structures with out-of-plane magnetization. Magnetic domains with in-plane magnetization have also been observed by MFM in nitrided austenitic stainless steels [12,13]. Having a magnetic γ N layer on a non-magnetic substrate (underlying fcc γ phase of austenitic SS has paramagnetic characteristics) in addition to its enhanced corrosion resistance and high strength may have industrial applications similar to those of iron nitrides which are potential candidates in high density magnetic recording applications.…”