Epitaxial Growth of (111) TbFe 2 by Sputter Deposition
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ABSTRACT The effect of in-plane strain in (111)-oriented epitaxial TbFe2 films on the magnetization orientations was studied. Magnetocrystalline anisotropy, shape anisotropy, and magnetoelastic energy were calculated to determine the magnetization orientation in the presence of various in-plane strains. Theoretical considerations indicate that a compressive strain smaller than -0.065% can induce an out-of-plane magnetization. DC magnetron sputtering from Tb and Fe elemental targets was used to grow 50, 100, 200, and 400 A thick epitaxial TbFe2 (111) films at 600'C on (1120)-oriented sapphire substrates with 1000 A thick epitaxial Mo(110) buffer layers. The growth rate of the TbFe2 (111) films was 1.44 A/sec. X-ray diffractometry, Rutherford backscattering spectrometry, and vibrating sample magnetometry were used to characterize the crystal structure, epitaxial orientation, composition, stress and strain state, and magnetic properties of the TbFe2 films. The TbFe2 (111) films were epitaxial with twins rotated by 600 and were in tensile strain states with the resulting in-plane magnetization. INTRODUCTION TbFe2 is a giant magnetostrictive material with the largest known room temperature magnetostriction 1 . Large magnetostriction is potentially useful for sensors, actuators or surface-acoustic-wave applications. In the magnetostrictive applications, the applied magnetic field changes the magnetization direction and then changes the dimensions of the
material. On the other hand, we can use the inverse magnetostrictive effect to control the magnetization orientation by applying stress on the material. The effect of film stresses on the anisotropy orientation have been studied in amorphous TbDyFe films with the result that tensile stresses induce in-plane anisotropy and compressive stresses induce out-of-plane anisotropy 2. In this experiment we grow (111)-oriented epitaxial TbFe2 films and study the effect of film strains on the magnetization orientation. Epitaxial TbFe2 (111) films with out-of-plane magnetization are potentially useful for magneto-optical recording applications. The total magnetic anisotropy of (111)-oriented epitaxial TbFe2 films in the presence of various in-plane strains is calculated to determine the orientation of the magnetization. These films have been successfully grown on (1120)-oriented sapphire substrates with 1000 A Mo buffer layer at 600'C. The crystal structure, epitaxial orientation, composition, stress and strain state, and magnetic properties of the TbFe2 films are investigated. Strain and magnetization data from this experiment are compared with those from calculation of the anisotropy. MAGNETIC ANISOTROPY Magnetocrystalline anisotropy, shape anisotropy, and magnetoelastic energy were considered to determine the magnetization orientations in the epitaxial TbFe2 (111) films. Using 79
Mat. Res. Soc. Symp. Proc. Vol. 384 01995 Materials Research Society
Figure 1: Film coordinate system for (1 1)-oriented TbFe2 films.
Using the film coordinate system in Figure 1, we can write the ma
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