Generation of micro/nano-scaled magnetic structures on AISI 304L austenitic stainless steel by ion beam nitriding

Nitriding of austenitic stainless steel at moderate temperatures (~400ºC) leads to the formation of the supersaturated nitrogen solid solution often called in the literature “expanded austenite” or γN phase [1]. This causes an enhancement of the microhardness and the wear resistance without loss of the corrosion resistance. Moreover, this phase shows ferromagnetic behavior, whose origin is linked to the expansion of the austenite (γ) lattice due to the incorporation of nitrogen atoms into interstitial positions [2].

The influence of the processing temperature and time on the structural and magnetic properties of AISI 304L austenitic stainless steel, after ion beam nitriding, has been investigated by x-ray diffraction (XRD), nuclear reaction analysis (NRA), magneto-optical Kerr effect (MOKE) magnetometry and atomic/magnetic force microscopy (AFM/MFM). Furthermore, periodic arrays of ferromagnetic structures in the micrometer and sub-micrometer range have been prepared after nitriding through either 2000 mesh Cu transmission electron microscopy grids (mesh size of 7.5 x 7.5 µm2, 12.5 µm pitch, 20 µm thickness and 3.05 mm diameter) or self-assembled porous alumina membranes (5 µm thickness), both acting as shadow masks. The local character of the induced ferromagnetism is confirmed by magneto-optical Kerr effect measurements together with magnetic force microscopy imaging.

[1] G. Abrasonis, et al., J. Appl. Phys. 97, 083531 (2005)
[2] O. Öztürk and D.L. Williamson, J. Appl. Phys. 77, 3839 (1995)