Ultrafast magneto-optical response of iron thin films

Abstract

Optical pump probe techniques are utilized to measure the time-resolved magneto-optical Kerr effect ͑TRMOKE͒ of a ferromagnetic iron film at room temperature in air. We focus on the interpretation of the TRMOKE signal, and find the experimental data to be consistent with a simple phenomenological model. Nonmagnetic contributions are present in the TRMOKE signal up to 100 ps after excitation. Without making further assumptions, this prevents a determination of the true magnetization dynamics. The initial magnetization does not change its direction, and within the first picoseconds there is no detectable dependence of the magnetization dynamics on the external magnetic field.

Investigation of transient linear and circular birefringence in metallic thin films

“…We wish to detect the time-dependent rotation of an initially linearly polarized probe beam that arises from pump-induced changes in r sp or r ps . These reflection coefficients may be modified through changes in either the magnetization or the optical constants of the sample [35]. In our experiments the fractional change in the magnetization after the electron system has thermalized is expected to be much larger than the fractional change in the optical constants, so magnetic changes should dominate the changes in r sp and r ps .…”

Femtosecond Spectrotemporal Magneto-optics

“…In the case of metallic ferromagnets, however, the effect of the pump is more subtle, and several questions have been raised about the interpretation of the observed drop in the MO contrast during the first hundreds of femtoseconds following the pump excitation. For example, recent results have shown a discrepancy between the dynamics of differential rotation and ellipticity measured simultaneously with the pump-probe technique [6,9,11]. These observations seem to break the proportionality relationship between the magnetization and Voigt vector, which is the basic assumption of linear magneto-optics.…”

“…DOI During the last few years, femtosecond time-resolved magneto-optics opened the way to measure the magnetization dynamics in ferromagnetic metals on the subpicosecond temporal scale [1,2]. Several experimental configurations have been reported based on the thirdorder (i.e., pump-probe) magneto-optical (MO) effect [3][4][5][6][7][8][9][10][11][12], magnetization-dependent surface second harmonic generation [13][14][15][16], and time-resolved two photon photoemission [17,18]. In contrast to the techniques based on photoconductive switches, in which the magnetization dynamics is triggered by a pulsed magnetic field in the picosecond time scale [19][20][21][22][23], a femtosecond temporal resolution can be achieved with MO techniques by inducing the magnetization dynamics via the absorption of an ultrashort laser pulse (the pump pulse).…”

“…In that case, one would expect to observe a spectral signature in the MO response, associated with the population bleaching. The spectral probing of CoPt 3 [5] and Fe [11] was previously performed with a probe wavelength at both 800 and 400 nm. In the first case the results did not display significant changes, therefore pleading in favor of the interpretation of the dynamical response in terms of the spin dynamics.…”

Efficiency of ultrafast laser-induced demagnetization in GdxFe100−x−yCoMedapalli1, Razdolski2, Savoini3 et al. 2012Phys. Rev. B323265View full textAdd to dashboardCite

“…[8][9][10][11][12][13][14] Although in most cases the demagnetization is not complete, being often at the level of only a few percent, the majority of this research has been focused on understanding the time scale of this demagnetization and on novel channels of angular momentum transfer from the spin system. 1 At the same time, however, it has been noted that in the case of incomplete demagnetization the rate at which the magnetization drops might have nothing to do with the characteristic interaction time of the spins with other reservoirs of energy and angular momentum (electrons and phonons).…”