Magnetoelastic coupling and Delta E effect in TbxDy1 - x single crystals

The elastic moduli of the highly magnetostrictive Tb_xDy_1-x alloys (x=0.5, 0.6, and 0.67) were measured at 77 K under conditions of constant magnetic field and constant magnetic induction. From these values the magnetic contribution to the moduli (intrinsic ΔE effect) and magnetoelastic coupling factor k were calculated. For Young's moduli measured under constant flux density (magnetically blocked conditions), it was found that E^B∼20 to 50 GPa. For measurements made while maintaining a constant magnetic field (magnetically free conditions), it was found that Young's moduli E^H minima range from ∼3 to 5 GPa. Such large differences between E^B and E^H yield magnetoelastic coupling factors in excess of 0.9. Theoretical expressions of the magnetic contribution to the elastic compliance, (1/E^H-1/E^B), were derived using the single vector magnetization rotation model.