Preparation and stability of NdDyFeCoTi magneto-optical amorphous films

Abstract

Because the light rare-earth element Nd makes a significant contribution to the Kerr effect and the heavy rare-earth element Dy can improve the coercivity and perpendicular anisotropy, NdDyFeCoTi magneto-optical material was studied. The alloy targets were prepared by a vacuumm melting method with compositions (NdxDy1−x)25(Fe0.65Co0.30Ti0.05)75 with x=0.2–0.3. Because of the addition of Ti, the mechanical strength of the target was improved. Amorphous NdDyFeCoTi films were prepared by rf magnetron sputtering onto glass substrates at zero bias, a low Ar pressure of 3–7 mTorr, and a low-input sputtering power of 100–300 W. The magnetic and magneto-optical properties of these films were studied by VSM, Kerr hysteresis tracer, and Auger electron spectroscopy. The Kerr angle θk of 0.3° and the coercive force Hc of 3–5 kOe have been found. The stability of the films was examined by exposure in air for one month and annealing at 100–250 °C. The magneto-optical properties of the films exhibit no obvious change after exposure in air, but after annealing at 200–250 °C the properties of NdDyFeCoTi with a SiO2 protective layer became poor. As a result, it is necessary to improve the stability of NdDyFeCoTi magneto-optical films by a protective layer without oxygen such as AlN.