Structure and magnetic properties of epitaxial terbium-iron thin films

TbFe{dollar}sb2{dollar} is a giant magnetostrictive material which has the largest known room temperature magnetostriction constant. The large magnetostriction constant suggests that we can manipulate the magnetic anisotropy of the material using small strains. Other research groups have grown amorphous and polycrystalline TbFe{dollar}sb2{dollar} films; however, these films lose giant mangetostriction because of diordered atomic structure in the amorphous films and random grain orientation in the polycrystalline films. Single-crystal structure is needed to achieve the large magnetostriction, so epitaxial growth of TbFe{dollar}sb2{dollar} thin films is necessary. The goal of this research is to grow epitaxial TbFe{dollar}sb2{dollar} films and study the effect of film strain on magnetic anisotropy.; A technique was developed to grow epitaxial TbFe{dollar}sb2{dollar}films using DC magnetron sputtering. The films were grown in a UHV system using elemental Tb and Fe sputtering targets and single-crystal {dollar}rm Alsb2Osb3{dollar}, MgO, and CaF{dollar}sb2{dollar} substrates. (110) -oriented Mo, W, and Nb were used as buffer layers to provide the base for epitaxial growth and to prevent chemical reactions between the TbFe{dollar}sb2{dollar} films and the substrates. On the Mo and W buffer layers the TbFe{dollar}sb2{dollar} film is (111) -oriented but on the Nb buffer layer it is (110) -oriented.; Preliminary calculation of magnetostrictive anisotropy in TbFe{dollar}sb2{dollar}(111) films predicts that compressive strain greater than 0.5% will induce perpendicular magnetization while tensile strain greater than 0.5% will induce an in-plane magnetization. Epitaxial growth on CaF{dollar}sb2{dollar} provides compressive thermal strain of 0.51%, and SQUID measurements confirmed that these samples did have perpendicular magnetization. On the other hand, {dollar}rm Alsb2Osb3{dollar} provides tensile thermal strain of 0.56%, and SQUID measurements showed the films on {dollar}rm Alsb2Osb3{dollar} were in-plane. The values of strain on these three substrates were determined by strain measurement from synchrotron radiation. X-ray epitaxial quality measurements revealed a new orientation relationship, R30{dollar}spcirc{dollar}, at the TbFe{dollar}sb2{dollar}(111)/Mo(110) and TbFe{dollar}sb2{dollar}(111)/W(110) interfaces.; For epitaxial TbFe{dollar}sb2{dollar}(110) films we predicted two {dollar}langle111rangle{dollar} easy axes in the plane. However, torque magnetometry measurements showed only one easy axis, along the (110) direction. Theoretical calculations indicated that a tensile film strain can make the easy axis change from (111) to (110) direction. By measuring film strain and anisotropy constant from synchrotron radiation and torque magnetometry, respectively, we confirmed that tensile strain in the film had made the easy axis change.; Finally, some initial work was performed to model rotational hysteresis loss in the torque curves. Stoner-Wohlfarth model was applied to describe the rotational behavior of magnetization under the conditions of the torque experiments. Although it is not strictly applicable in this situation, it did provide an insight into the origin of the hysteresis loss.