Magnetomechanical behaviour of rare earth iron-aluminium compounds

The DC field and pressure dependencies of the magnetic induction (B) and magnetostrictive strain (λ) have been measured at room temperature in Terfenol-D (Tb_0.3Dy_0.7Fe_1.95 ) and in the compound Tb_0.3Dy_0.7(Fe_0.9 Al_0.1)_1.95. From these data the static differential permeability (μ) and strain coefficient (d₃₃=dλ/dH) have been obtained. A comparison of their magnetostrictive responses indicates that the magnetocrystalline anisotropy is reduced by the addition of Al to Terfenol-D. A slight lowering of d₃₃ with Al content is attributed to a reduction in magnetoelastic coupling, also seen in a lower magnetomechanical coupling coefficient. The work done by either compound against the applied pressure for different isostatic fields has been calculated. From these curves the residual stress levels, T₀, are substantially lower than those reported previously in Tb_0.27Dy_0.73Fe₂, indicating that in the present compounds T₀ is due mainly to inhomogeneities and defects, rather than anisotropy