ABSTRACT
The Heisenberg-Dirac intra-atomic exchange coupling is responsible for the formation of the atomic spin moment and thus the strongest interaction in magnetism. Therefore, it is generally assumed that intra-atomic exchange leads to a quasi-instantaneous aligning process in the magnetic moment dynamics of spins in separate, on-site atomic orbitals. Following ultrashort optical excitation of gadolinium metal, we concurrently record in photoemission the 4f magnetic linear dichroism and 5d exchange splitting. Their dynamics differ by one order of magnitude, with decay constants of 14 versus 0.8 ps, respectively. Spin dynamics simulations based on an orbital-resolved Heisenberg Hamiltonian combined with first-principles calculations explain the particular dynamics of 5d and 4f spin moments well, and corroborate that the 5d exchange splitting traces closely the 5d spin-moment dynamics. Thus gadolinium shows disparate dynamics of the localized 4f and the itinerant 5d spin moments, demonstrating a breakdown of their intra-atomic exchange alignment on a picosecond timescale.
ABSTRACT
Using analytical calculations as well as computer simulations, we show that antiferromagnets can be switched on a time scale of picoseconds using THz laser pulses only. This all-optically triggered switching mechanism rests on the coordinated dynamics of the two interacting sublattices with an inertial character. We calculate the resonance frequencies in the nonlinear regime, the orbits, and estimate the field strength required for switching analytically. Furthermore, we demonstrate that ferrimagnets can be switched similarly at their compensation point.
