Ultrafast reduction of the total magnetization in iron

Abstract

Surprisingly, if a ferromagnet is exposed to an ultrafast laser pulse, its apparent magnetization is reduced within less than a picosecond. Up to now, the total magnetization, i.e., the average spin polarization of the whole valence band, was not detectable on a sub-picosecond time scale. Here, we present experimental data, confirming the ultrafast reduction of the total magnetization. Soft x-ray pulses from the free electron laser in Hamburg (FLASH) extract polarized cascade photoelectrons from an iron layer excited by a femtosecond laser pulse. The spin polarization of the emitted electrons is detected by a Mott spin polarimeter.

Stoner versus Heisenberg: Ultrafast exchange reduction and magnon generation during laser-induced demagnetization

“…The possible contributions of reduced exchange splitting and magnon excitation have been discussed over the last years, but without strong consensus to date 9,10,22,28,30,38,[43][44][45][46] . Some authors observe a change of exchange splitting during ultrafast demagnetization 38,[44][45][46] , while others do not 30 .…”

Spin-Resolved Valence Photoemission

“…A nondispersing SS peak was identified close to E F . Spin analysis of selected spectra then revealed that the peaks close to the E F , especially for 67 eV, 12 , and 72 eV, 20 , had minority spin character. As predicted the SS peak is absent at 67 eV, 16 which is close to the X point [168].…”

“…More recently experiments have established that upon laser excitation, itinerant ferromagnets lose their longrange magnetic order within a few hundred fs [268][269][270][271]. Very recently, for example, the ultrafast surface demagnetization of an 8 ML Fe(110) film was explored in a near IR (1.5 eV)/X-ray (182 eV) pump-probe experiment using a Ti-sapphire laser synchronized to the FLASH FEL at DESY [12]. By probing the spin polarization of the cascade electrons, the total magnetization of the sample was shown very directly to be quenched within a 1/e decay time of 100 fs.…”

“…Yet higher energies are available from the free-electron laser sources that have been, or are currently being, developed worldwide. Though these sources have been used for some time for gas-phase spin-polarized photoelectron spectroscopy, the first spin-resolved publication for surfaces has only recently emerged [12]. Synchrotron radiation has on the other hand been very widely used for SRPES, and facilities exist at, for example, the Advanced Photon Source (APS), the Advanced Light Source (ALS), the Swiss Light Source (SLS), the European Synchrotron Radiation Facility (ESRF), Soleil, BESSY, DELTA, the Photon Factory KEK, the Hiroshima Synchrotron Radiation Centre (HSRC), MAX-Lab, and the Synchrotron Radiation Research Centre (Hsinchu, Taiwan) [13][14][15][16][17][18][19][20][21][22].…”

Spin-resolved photoelectron spectroscopy using femtosecond extreme ultraviolet light pulses from high-order harmonic generation

“…It has been demonstrated earlier that the combination of a Mott spin detector and FEL radiation can be used for studies of laserinduced changes in the total magnetization of Fe by measuring the spin polarization of the secondary electrons. 22 However, the low repetition rates of available FELs in the Hz range and the limitation of the maximum pulse intensity due to Coulomb repulsion in the resulting dense electron clouds (see Sec. IV) restrict the number of photoelectrons in such experiments.…”