M. Fukuzumi

Positron Annihilation Study on Defects and Phase Transition of FeRh Alloys Subjected to High-Speed Deformation

The relations between vacancy-type defects in Fe-40, 45, and 50 at%Rh alloys and stress-induced phase transitions from a B2 phase have been examined by XRD, TEM, and positron annihilation experiments. The specimens were deformed at room temperature by a high-speed compression machine, and the natures of related vacancies and vacancy clusters were examined. The results reveal that structural Rh vacancies exist in non-stoichiometric FeRh alloys, and that lifetimes of the long-lifetime components of the introduced defects change in various manners, depending upon the deformation conditions.

Positron Annihilation Study on Point Defects in Fe-Rh Alloys

In order to investigate the production and diffusion mechanisms of defects in Fe-Rh intermetallic compounds, the positron annihilation lifetime and coincidence Doppler broadening (CDB) measurements are carried out for Fe-50at.%Rh alloys irradiated with 6 MeV and 28 MeV electrons at 100 K. A long lifetime component of about 250 psec is observed in the specimen irradiated with 6 MeV electrons. The result shows that vacancy clusters including 3 or 4 vacancies are formed during electron irradiation. Furthermore, the vacancy clusters remain stable up to about 360 K. The CDB results indicate that the atomic configuration around irradiation-induced vacancies strongly depends upon the electron energy and/or total electron fluence.

Modification of lattice structure and magnetic properties of Fe-Rh alloys by energetic electron irradiation

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.