Pulsed-laser-induced quenching of ferromagnetic order has intrigued researchers since pioneering works in the 1990s. It was reported that demagnetization in gadolinium proceeds within 100 ps, but three orders of magnitude faster in ferromagnetic transition metals such as nickel. Here we show that a model based on electron-phonon-mediated spin-flip scattering explains both timescales on equal footing. Our interpretation is supported by ab initio estimates of the spin-flip scattering probability, and experimental fluence dependencies are shown to agree perfectly with predictions. A phase diagram is constructed in which two classes of laser-induced magnetization dynamics can be distinguished, where the ratio of the Curie temperature to the atomic magnetic moment turns out to have a crucial role. We conclude that the ultrafast magnetization dynamics can be well described disregarding highly excited electronic states, merely considering the thermalized electron system.

The vortex state, characterized by a curling magnetization, is one of the equilibrium configurations of soft magnetic materials and occurs in thin ferromagnetic square and disk-shaped elements of micrometre size and below. The interplay between the magnetostatic and the exchange energy favours an in-plane, closed flux domain structure. This curling magnetization turns out of the plane at the centre of the vortex structure, in an area with a radius of about 10 nanometres--the vortex core. The vortex state has a specific excitation mode: the in-plane gyration of the vortex structure about its equilibrium position. The sense of gyration is determined by the vortex core polarization. Here we report on the controlled manipulation of the vortex core polarization by excitation with small bursts of an alternating magnetic field. The vortex motion was imaged by time-resolved scanning transmission X-ray microscopy. We demonstrate that the sense of gyration of the vortex structure can be reversed by applying short bursts of the sinusoidal excitation field with amplitude of about 1.5 mT. This reversal unambiguously indicates a switching of the out-of-plane core polarization. The observed switching mechanism, which can be understood in the framework of micromagnetic theory, gives insights into basic magnetization dynamics and their possible application in data storage.

We present an ultrafast route for a controlled, toggle switching of magnetic vortex cores with ultrashort unipolar magnetic field pulses. The switching process is found to be largely insensitive to extrinsic parameters, like sample size and shape, and it is faster than any field-driven magnetization reversal process previously known from micromagnetic theory. Micromagnetic simulations demonstrate that the vortex core reversal is mediated by a rapid sequence of vortex-antivortex pair creation and annihilation subprocesses. Specific combinations of field-pulse strength and duration are required to obtain a controlled vortex core reversal. The operational range of this reversal mechanism is summarized in a switching diagram for a 200 nm Permalloy disk.

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Based on the Fermi surface breathing model of Kamberský, a phenomenological extension of the ab initio density-functional electron theory is used to derive an equation of motion for the spin dynamics in magnets. It is shown that even in the simple case of a homogeneous magnetization M the damping term ͑1/ M͒M ϫ ͓␣dM / dt͔ of the commonly used Gilbert equation with the damping scalar ␣ has to be replaced by a term of the form ͑1/ M͒M ϫ ͓␣ = ͑M͒ · dM / dt͔ with a damping matrix ␣ = which depends on the orientation of M. Explicit calculations are performed for bulk, monolayers, and monatomic wires of Fe, Co, and Ni. The variation of ␣ = with an orientation of M is quite substantial already for the bulk materials ͑up to a factor of 4 in hcp Co͒ but most dramatic in the monolayers and monatomic wires in which for some orientations the damping is even zero. This represents an additional option for optimizing the magnetization reversal process in a magnetic nanostructure. It is shown that there is no simple relation between damping and magnetic anisotropy energy.

Cohesive energies, bulk moduli and equilibrium lattice constants have been calculated for the 4d and 5d transition metals with face-centred cubic crystal lattices (Rh, Pd, Ag and Ir, Pt, Au). For the total energy calculations according to the density functional theory on the local density approximation the authors have used an ab initio pseudopotential method. Two calculations have been performed for each element using either nonrelativistic or scalar-relativistic ionic pseudopotentials. The pseudo-wavefunctions and charge densities of the valence electrons have been represented by a mixed basis of plane waves and localised orbitals derived from the atomic d pseudo-wavefunctions. For the 5d metals they find a significant improvement of the results by the relativistic treatment, as expected because of their heavy atomic nuclei. In the case of the 4d metals the relativistic results are of similar quality as for the 5d metals, but now the nonrelativistic values are slightly closer to the experiment, possibly due to an error cancellation effect.

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