Structure and magnetic properties of MnBiDy(Sm) permanent magnetic films

We have studied crystal texturing and magnetic properties of MnBiDy(Sm) permanent magnetic films, with thicknesses varying from 60 to 1200 nm, fabricated by the thermal coevaporation method and subsequently annealed in a vacuum oven at temperatures ranging from 350–425 °C. X-ray diffraction analysis has shown that the samples exhibit low-temperature phase MnBi with a NiAs-type structure when the thicknesses of the samples are less than 250 nm. When the thicknesses are larger than 250 nm, however, the Bi3Mn2 phase also appears. Magnetic measurements have revealed that saturation magnetization σs=46–78 emu/g, residual magnetic induction Br=3.2–7.3 kGs, remnant magnetization ratio r=0.64–0.98, intrinsic coercive force Hc=2.2–7.3 kOe, and magnetic energy product (BH)m=3.33–14.3 MGOe. We have also found that Hc depends on the thickness of the sample, and reaches a maximum when the thickness d=400 nm. The origin of the coercive force may be understood by the nucleation and growth of reverse magnetic domains when d