Laser-induced manipulation of magnetic anisotropy and magnetization precession in an ultrathin cobalt wedge

Abstract

Ultrafast magnetization dynamics in an epitaxially grown Co wedge-shaped layer sandwiched between Pt films has been studied by means of time-resolved magneto-optics. By changing either the external magnetic field or the thickness-dependent anisotropy field, we were able to tune the magnetization precession, as it depends on the effective magnetic field affecting the sample. A particularly interesting possibility of tuning occurs at the range of thicknesses near the spin reorientation transition (at d 0 = 2.3 nm), where the effective anisotropy field changes sign. To describe the measured dynamics we propose a model based on ultrafast thermal changes of the effective anisotropy field as a mechanism of triggering precession of the spins.

Ultrafast changes of magnetic anisotropy driven by laser-generated coherent and noncoherent phonons in metallic films

“…Due to electron-phonon interaction this process takes place on subpicosecond time scale and often may be considered as an instantaneous rise of the lattice temperature T. The increase of T affects the values of the MCA parameters and Beff tilts from its equilibrium position. Such a scenario has been considered in a number of previous works and may be attributed to the modulation of MCA by non-coherent phonons generated as a result of optical excitation [7][8][9][10][11].…”

“…[14,15] and Ref. [7][8][9][10][11] respectively, but there is no way to compare quantitatively the contributions of these mechanisms to changes of the MCA as a result of direct optical excitation.…”

Laser-induced magnetization dynamics in a cobalt/garnet heterostructure

“…In this case we observe no polarization dependence of the oscillations. In general, the laser-induced precession can be excited due to an ultrafast laser-induced demagnetization typical for metallic magnets [11]. The demagnetization is seen as a sub-picosecond change of the magneto-optical signal measured at H = 4.6 kOe.…”

Irreversible modification of magnetic properties of Pt/Co/Pt ultrathin films by femtosecond laser pulses

“…Details of the modeling of the temperature dynamics are discussed in Ref. 15. Crucial here is also the absence of the long-term heat transfer resulting from heat accumulation.…”

“…12,13 As light also carries energy, it may increase the temperature in metals due to absorption. For low energies of light pulses, the thermally induced changes of the magnetization and magnetic anisotropy are reversible and may trigger a magnetization precession, 14,15 while with higher light intensities, irreversible changes of the structure can be achieved. Employing few-nanosecond laser pulses, a decrease of the magnetic anisotropy in Pt/Co/Pt systems 16,17 was observed; on the contrary, for Au/Co/Au the possibility of creating the out-of-plane magnetization state with semi-continuous laser irradiation was demonstrated.…”