Electronic Grüneisen parameter and thermal expansion in ferromagnetic transition metal

We report the measurement of the electronic Gruneisen parameter γe of the ferromagnetic transition metal nickel. In this measurement, the electronic thermal expansion was differentiated from other thermal contributions by simultaneously monitoring the laser-induced ultrafast stress and structural dynamics in the time domain 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. The result indicates that the local magnetic moment, which persists in the paramagnetic state of nickel, does not significantly contribute to the thermal expansion.