We present ultra-high-resolution dilatometric studies in magnetic fields on a quasi-two-dimensional organic conductor $\kappa$-(D8-BEDT-TTF)$_{ 2}$Cu[N(CN)$_{ 2}$]Br, which is located close to the Mott metal-insulator (MI) transition. The obtained thermal expansion coefficient, $\alpha(T)$, reveals two remarkable features: (i) the Mott MI transition temperature $T_{ MI}$ = (13.6 $\pm$ 0.6)\,K is insensitive to fields up to 10\,T, the highest applied field; (ii) for fields along the interlayer \emph{ b}-axis, a magnetic-field-induced (FI) phase transition at $T_{ FI}$ = (9.5 $\pm$ 0.5)\,K is observed above a threshold field $H_c \sim$ 1 T, indicative of a spin reorientation with strong magneto-elastic coupling.
Categories: cond-mat.str-el cond-mat.supr-con