Magnetostrictive strains in polycrystalline FePdRh alloy

Abstract

The conventional magnetostrictive property was studied in the polycrystalline Fe–30Pd–4Rh alloy. The alloy was solution treated at 950°C for 1.5h and then water quenched. At room temperature, the alloy has a mixed adaptive (or intermediate) martensite structure with ao=3.784Å and co=3.514Å. At a lower temperature (e.g., T=150K), the full martensitic transformation is finally completed, and an expansion of the c axis with Δc∕co≃6.8% was observed. The thermal expansion coefficient, (1∕T)(Δa∕ao), is +3.84×10−6K−1 between 300 and 150K. From the electrical resistance (R) measurement between 300 and 4K, we confirm that the second, or final, martensitic transformation temperature (TIM) is approximately 170K. In addition, at room temperature, the saturation magnetization Ms(300)=655G, while at T=5K, Ms(5)=808G. Because an external field (H) may rotate Ms in the sample plane of Fe–Pd–Rh alloy, we find that, at T=300K, its saturation magnetostriction λs=62ppm, and at T=77K, λs=115ppm. There are at least two advantages on using the Fe–Pd–Rh alloy as the material for a magnetic-type microactuator or spring: (1) the alloy is ductile, and (2) at room temperature, the magnetostrictive susceptibility (Δλ)∥s∕(ΔH) is high, about 0.8ppm∕Oe at low field (H=50Oe).