Potential energy of a magnet with magnetic moment \\\\(\\vec{M}\\\\) placed in a magnetic field \\\\(\\vec{B}\\\\) is given by \\\\(U=-\\vec{M}.vec{B}\\\\)\\\\(=-MBcos\ heta\\\\)which is smallest for \\\\(\ heta=0\\\\)Hence \\\\(U_{min}=-MB=-0.4\ imes 0.16J\\\\)\\\\(=-0.064J\\\\)