The measurement of magnetostriction in ferromagnetic thin films

The application of a magnetic field parallel to a ferromagnetic film deposited on one side of a cantilevered substrate causes a small deflection of the free end. This deflection can be measured and the magnetostriction determined since the magnetostriction is proportional to the deflection. An instrument has been devised which can measure the deflection as a function of the applied field. This is accomplished as follows: the cantilevered substrate with the film on the upper side forms one plate of a capacitor which is part of the tuning capacitance of an oscillator operating at l0 MHz. The deflection of the free end causes a change in frequency of about 10 to 100 Hz. which is easily measured. The sign of the magnetostriction is immediately discernible from the increase or decrease in oscillator frequency. The instrument is calibrated by hanging a known weight from the free end of the substrate. Magnetostriction constants as small as3 \times 10^{-7}and as large as40 \times 10^{-6}have been measured.