Toshiyuki Matsui1

1, Osaka Prefecture University, Sakai, , Japan

Iron-rhodium ordered alloy with B2 (CsCl-type) crystal structure has a first-order phase transition from the low-temperature antiferromagnetic (AF) phase to the high-temperature ferromagnetic (FM) phase near room temperature. It is also found that this transition is accompanied by a volume increase of 1–2%, and a reduction in resistivity. Much interest has been recently paid to this material mainly owing to its potential technological applications, such as data storage media using thermally controlled AF–FM coupling phenomena, micro-electromechanical systems and spin valve-based devices.
We have ever reported that the ion beam irradiation at various energies ranging from GeV to keV orders can induce the FM state in FeRh bulk and film samples without any structural changes below room temperature at which they are originally in the AF state. In addition, further ion beam irradiation causes the change from the FM state to the paramagnetic (PM) state accompanied by a structural change from the B2-type to A1 (disordered fcc)-type structures. During the course of these studies, the change in the magnetization of the ion-irradiated FeRh is considered to be mainly dominated by elastic collisions between the ions and the samples, which generate lattice defects in B2-type FeRh. On the basis of such knowledge, we have attempted to fabricate micro scale magnetic patterns using the ion microbeam technique. If such magnetic patterns can be easily fabricated in samples by ion microbeam irradiation, novel applications for patterned media may be feasible.
In addition, we also realized that ferromagnetic layered structure has been made at sub-surface of the antiferromagnetic FeRh bulk samples by high energy He ion beam irradiation, because the beam energy solely determines the regions where the elastic energy deposited. The possibility three dimensional magnetic patterning for the FeRh thin films and bulks by high and low energy ion beam irradiation, such as 1 keV Ar, 30 keV Ga, 2-6MeV H and He ion beam will be discussed based on the experimental results of SQUID, MFM, XMCD and XMCD-PEEM. We will also discuss the depth directional magnetic modification at ultra-surface region of the samples by using the energetic cluster ion beam irradiation such as C2, C3 and C60. The results of the depth-directional XMCD analysis techniques was used for such communication.