Electronic Gr\"{u}neisen Parameter In Paramagnetic Nickel

We have conducted the first measurement of electronic Gr\"{u}neisen parameter \textit{$\gamma $}$_{e}$ in the paramagnetic state of ferromagnetic transition metal nickel by monitoring the laser-induced ultrafast stress dynamics using femtosecond electron diffraction. This method overcomes the restriction of traditional low-temperature methods and offers a unique path to study electronic thermal expansion in magnetic metals. Our measurement indicates that the local magnetic moment that persists in the paramagnetic state of nickel does not contribute significantly to electronic thermal expansion. This result would serve as an important test of current models regarding the magnetism in ferromagnetic transition metals.