Modification of lattice structure and magnetic properties of Fe-Rh alloys by energetic electron irradiation
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Modification of lattice structure and magnetic properties of Fe-Rh alloys by energetic electron irradiation Masafumi FUKUZUMI, Ryoichi TANIGUCHI1, Seiji KOMATSU2, Fumihisa ONO2 and Akihiro IWASE1 Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuencho, Sakai, Osaka 599-8531, Japan 1 Research Institute for Advanced Science and Technology, Osaka Prefecture University, 1-2 Gackuencho, Sakai, Osaka 599-8570, Japan 2 Department of Physics, Okayama University, 2-1-1 Tsushima-Naka, Okayama 700-8530, Japan ABSTRACT In order to modify the lattice structure and magnetic properties, we irradiate Fe-50at.%Rh alloys with 8 MeV electrons at room temperature. Effects of irradiation are investigated by using Superconducting QUantum Interference Device (SQUID) and X-Ray Diffractometer (XRD). Although the crystal structure is not changed by the irradiation and remains the B2 structure, the lattice parameter increases by about 0.1-0.3 % and the antiferromagnetic(AF)-ferromagnetic(FM) transition temperature decreases by 3-18 deg. with increasing the electron fluence. The present result shows that energetic electron irradiation can be used for the precise control of AF-FM transition temperature of Fe-50at.%Rh alloy. INTRODUCTION In the near equiatomic ordered Fe-Rh alloy, magnetic and structural transitions take place at several temperatures. On heating above 320 K, the first order antiferromagnetic(AF)-ferromagnetic(FM) transition occurs without changing the crystal structure but with a 1 % volume expansion. From the neutron diffraction pattern [1], the magnetic moments of Fe and Rh atoms for the ferromagnetic state are 3.1 µB and 1.0 µB at room temperature, respectively. In contrast, for the antiferromagnetic state, the magnetic moment of Fe atom is 3.3 µB and Rh atom has no magnetic moment. It is well known that the magnetic transition is very sensitive to composition, heat treatment, magnetic field and external pressure. It has been reported that when the Fe-Rh alloys are put under the influence of external high pressure, the antiferromagnetic state is stabilized, and the AF-FM transition temperature increases [2]. The transition temperature strongly depends on the change in Fe content； Fe51.5Rh48.5 alloy is still ferromagnetic even at liquid helium temperature [3]. Resent studies have also shown that the lattice structure of Fe-Rh alloys is changed by high speed deformation [4,5]. From these previous results, we expect that the magnetic properties and the lattice structure of Fe-50at.%Rh alloys can be modified by high energy particle irradiations, because such irradiations induce lattice defects (interstitial atoms and vacancies) into materials, causing lattice expansion, realize “thermal spike state” and/or “high pressure state” locally in
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materials, and cause the selective diffusion of the constituent elements, which changes the composition in irradiated region. In this paper, we report the effects of energetic electron irradiation on the lattice parameter and the AF-FM transition temperatur
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