Spin reorientation and magnetoelastic properties of ferromagnetic Tb1-xNdxCo2 systems with a morphotropic phase boundary

The spin reorientation (SR) and magnetoelastic properties of pseudobinary ferromagnetic $\mathrm{T}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{N}{\mathrm{d}}_{x}\mathrm{C}{\mathrm{o}}_{2}$ ($0\ensuremath{\le}x\ensuremath{\le}1.0$) systems involving a morphotropic phase boundary (MPB) were studied by high-resolution synchrotron x-ray diffraction (XRD), magnetization, and magnetostriction measurements. The easy magnetization direction of the Laves phase lies along the $\ensuremath{\langle}111\ensuremath{\rangle}$ axis with $xl0.65$, whereas it lies along the $\ensuremath{\langle}100\ensuremath{\rangle}$ axis for $xg0.65$ below Curie temperature (${T}_{\mathrm{C}}$). The temperature-dependent magnetization curves showed SR; this can be explained by a two-sublattice model. Based on the synchrotron (XRD) and magnetization measurements, the SR phase diagram for a MPB composition of $\mathrm{T}{\mathrm{b}}_{0.35}\mathrm{N}{\mathrm{d}}_{0.65}\mathrm{C}{\mathrm{o}}_{2}$ was obtained. Contrary to previously reported ferromagnetic systems involving MPB, the MPB composition of $\mathrm{T}{\mathrm{b}}_{0.35}\mathrm{N}{\mathrm{d}}_{0.65}\mathrm{C}{\mathrm{o}}_{2}$ exhibits a low saturation magnetization (${M}_{\mathrm{S}}$), indicating a compensation of the Tb and Nd magnetic moments at MPB. The anisotropic magnetostriction (${\ensuremath{\lambda}}_{\mathrm{S}}$) first decreased until $x=0.8$ and then continuously increased in the negative direction with further increase of Nd concentration. The decrease in magnetostriction can be attributed to the decrease of spontaneous magnetostriction ${\ensuremath{\lambda}}_{111}$ and increase of ${\ensuremath{\lambda}}_{100}$ with opposite sign to ${\ensuremath{\lambda}}_{111}$. This paper indicates an anomalous type of MPB in the ferromagnetic $\mathrm{T}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{N}{\mathrm{d}}_{x}\mathrm{C}{\mathrm{o}}_{2}$ system and provides an active way to design novel functional materials with exotic properties.