Magnetic and magnetoelastic behavior of epitaxialTbFe2/YFe2bilayers

Abstract

We report on magnetic hysteresis and magnetoelastic stress measurements on a series of (110) ${\mathrm{TbFe}}_{2}(t)/{\mathrm{YFe}}_{2}$ $(1000 \AA{})$ bilayers $(t=300,$ $600,$ $1000,$ and $1300 \AA{})$ grown by molecular-beam epitaxy. The magnetization curves show large jumps that we have explained as due to the different magnetization contribution of both kinds of magnetically soft $({\mathrm{YFe}}_{2})$ and hard $({\mathrm{TbFe}}_{2})$ blocks, which, on the other hand, hardly show magnetic interaction for $t>300 \AA{}.$ In these cases, the hysteresis loop of the individual ${\mathrm{TbFe}}_{2}$ block is determined. The magnetoelastic stress measurements were performed along the main symmetry directions by using a cantilever capacitive method. They allowed us to determine the whole second-order magnetoelastic stress parameters: ${b}_{0}$ [associated to combined volume and tetragonal magnetostriction (MS)], ${b}_{1}$ (to tetragonal MS alone), and ${b}_{2}$ (to rhombohedral MS), at temperatures between 10 and 300 K. The ${b}_{0}$ values are about one order of magnitude lower than the ${b}_{1}$ and ${b}_{2}$ ones. $|{b}_{2}|$ smoothly rises on increasing the ${\mathrm{TbFe}}_{2}$ block thickness, whereas ${b}_{1}(t)$ peaks at $\ensuremath{\sim}1000 \AA{}.$ A competition between volume and interface magnetoelastic stresses could explain this fact. The thermal dependence of ${b}_{1}$ and ${b}_{2}$ indicates a single-ion crystal-electric-field origin for the magnetoelastic coupling and suggests a somehow rough interface between ${\mathrm{TbFe}}_{2}$ and ${\mathrm{YFe}}_{2}$ blocks.