Discovery of Giant Magnetostriction in Amorphous RFe₂B (R=Sm, Tb) Alloys

Compared with the conventional magnetostriction in Ni alloys which are in the order of several tens ppm (Parts Per Million =10^(-6)), RFe₂(R = rare earth element) Laves Phase intermetallic compounds show large saturation magnetostriction in the range of a few thousands ppm. However, the large external magnetic field necessary to obtain saturation magnetostriction has due to large magnetocrystalline anisotropy energy restrained the application of magnetostriction materials in RFe₂ intermetallic compounds. As a result of its solution, the largest published value of effective giant magnetostriction in a low external magnetic field (less than a few hundred Oe) is reported in this paper by means of amorphisation of RFe₂ intermetallic compounds with the addition of boron, as a half metal. For the amorphous (SmFe₂)_(0.97) B_(0.03) alloys, the effective magnetostriction of -545 and -610×10^(-6) is obtained at 400 and 1,000 Oe, respectively. Moreover, the effective magnetostriction of 590 and 630×10^(-6) in the amorphous (TbFe₂)_(0.98) B_(0.02) alloys is also found at 400 and 1,000 Oe, respectively. This result will provide a clue to understanding the effect of half metal on anomalous increase of the effective giant magnetostriction and attract the great attention for magnetostriction applications.