Heat Treatment for the Stabilization of Hydrogen and Vacancies in Electrodeposited Ni-Fe Alloy Films

In an effort to realize the long term stability of the magnetostrictive property of electrodeposited Ni-Fe alloy films, heat treatments needed for eliminating the possible effect of hydrogen and hydrogen induced vacancies have been investigated, mainly by use of thermal desorption spectroscopy. While metal atom vacancies begin to move only above similar to 500 K, hydrogen atoms can undergo slow motion and concomitant changes of state at room temperature, and are therefore believed to be a major cause of the long-term drift of the magnetism. Hydrogen atoms dissolved on regular interstitial sites can be completely removed by high-frequency pulse heating to 668 K, and those trapped by vacancies with relatively low binding energies by additional heat treatments to 453 K for over 1 h. This combination of heat treatments was found to reduce substantially the change of state of hydrogen during subsequent aging tests (383 K for 400 h), and proved to be effective for ensuring the long-term stability of magnetostrictive Ni-Fe film sensors. [doi: 10.2320/matertrans.MRA2008199]