Magnetic properties of thin film and granular Dy50Fe50 as a function of size

Thin amorphous Dy50Fe50/A layers are prepared by sputtering to understand t he influence of the spacer layer A on magnetic properties in the DyFe thick ness regime where size effects are also important. The spacer layer A in th is work is either Ti or Ca and we compare to our earlier work involving a s pacer layer of Mo. The Dy50Fe50 layer is amorphous and Mossbauer spectrosco py indicates that two types of Fe site are present. Finite size effects man ifest themselves below a size of 10 nm in a reduction of magnetic ordering temperature T-C and coercivity H-C. For equal values of d, the reduction of T-C and H-C is larger for the system with a Ti or Mo spacer layer as compa red to the Ca spacer layer. We argue that both size and the structure of th e interface are important in lowering H-C and T-C. The temperature dependen ce of coercivity is also studied and suggests that magnetic reversal via do main wall movement occurs in our thinnest films. (C) 2000 American Institut e of Physics. [S0021-8979(00)52108-2].