Directly sputter synthesized high-energy product Sm-Co based ferromagnetic films

Abstract

Different target configurations have been used to directly synthesize Sm-Co based films by selectively thermalized rf sputtering onto heated substrates in an in-plane magnetic field. Samples have been sputtered so that in certain cases a systematic gradient in Sm-to-Co concentration was created along the length of the substrates and in other cases so that films of a fixed uniform composition were deposited. Small subregions of a single substrate then serve as samples of a specific composition. For the Sm-to-Co composition range from 70 to 95 at. % Co gradient synthesized samples exhibit high magnetization and moderate intrinsic coercive forces. The maximum energy product of 20 MG Oe was obtained for a sample with 90.6 at. % Co containing mostly the Sm2Co17 phase. In addition, samples were synthesized from uniform composition targets at certain fixed compositions. Films sputtered from uniform composition Sm2(Co, Fe, Zr)17 targets exhibited square in-plane hysteresis loops and static energy products up to 21.2 MG Oe. It was observed that uniform composition SmCo5 films could be grown which exhibited either the (200) or the (110) texture as a function of the sputtering rate. Relatively higher sputtering rates of approximately 5 Å/sec resulted in the (200) texture growth pattern while lower rates resulted in (110) textured films. These differently textured SmCo5 films differ in both their microstructure and magnetic properties. The (110) textured film are finer in microstructure and magnetically harder than the (200) films. The uniform composition SmCo5 films of either texture in general were of smaller grain size and higher coercive forces than the SmCo5 subregions from films sputtered with a composition gradient spanning the 1–5 phase. A uniform composition SmCo5 film sputtered at 1.5 Å/sec which was (110) textured exhibited an intrinsic coercive force of 23 kOe and an energy product of 18 MG Oe at −63 °C. The high-energy products reported here are due to both the high induction and to the squareness of the in-plane hysteresis loops when measured in the direction parallel to the field applied during the sputter synthesis.