Distinctive Picosecond Spin Polarization Dynamics in Bulk Half Metals

Abstract

Femtosecond laser excitations in half-metal (HM) compounds are theoretically predicted to induce an exotic picosecond spin dynamics. In particular, conversely to what is observed in conventional metals and semiconductors, the thermalization process in HMs leads to a long living partially thermalized configuration characterized by three Fermi-Dirac distributions for the minority, majority conduction, and majority valence electrons, respectively. Remarkably, these distributions have the same temperature but different chemical potentials. This unusual thermodynamic state is causing a persistent nonequilibrium spin polarization only well above the Fermi energy. Femtosecond spin dynamics experiments performed on Fe_{3}O_{4} by time- and spin-resolved photoelectron spectroscopy support our model. Furthermore, the spin polarization response proves to be very robust and it can be adopted to selectively test the bulk HM character in a wide range of compounds.

Magnetic and Magneto-Optical Oroperties of Iron Oxides Nanoparticles Synthesized under Atmospheric Pressure

“…Due to the unique size-dependent magnetic properties, IONs are used in a wide variety of fields, including nanocatalysis, all-optical switching devices, microwave absorption, environmental remediation, chemical and biological sensors, energy generation and storage, biomedicine and biotechnologies, etc. [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. Among various IONs, magnetite (Fe 3 O 4 ) nanoparticles are one of the most promising, since they find application in such areas as high-density magnetic storage media, capacitor electrodes, development of sensors, ferrofluid, for absorption heavy metals [ 5 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ], have wide application in biotechnologies and biomedicine, for example, magnetic resonance imaging, hyperthermia, targeted delivery of drugs, detect and treat cancer [ 20 , 21 , 22 , 23 , 24 , 25 , 26 ].…”

Spin, time, and angle resolved photoemission spectroscopy on WTe2

“…Since both SARPES and T-ARPES are timeconsuming techniques, only few attempts have been made to combine them [22][23][24][25][26][27], and recently using a free electron laser source [28] or high harmonic generation (HHG) laser sources [29][30][31], which additionally provide tunability of the probing photon energy.…”

“…STARPES measurements are certainly demanding and time-consuming, but thanks to increasingly better control of HHG sources they can become a viable complementary alternative to synchrotron-based studies for different purposes [10]. A parallel theoretical effort to explore not only charge but also spin dynamics in out-of-equilibrium scenarios is required [27]. Indeed, a clear limitation of our work is that supporting calculations are performed at equilibrium.…”

Numerical solver for the time-dependent far-from-equilibrium Boltzmann equation

“…They reduce the computational time compared to straightforward deterministic solvers, yet they introduce a huge noise, especially when addressing spatial transport. Deterministic methods can overcome some of the shortcomings of stochastic methods (especially regarding transport) but become quickly prohibitively expensive when used for the scattering, and are applied only to very simplified forms of the scattering term [29][30][31] . All the mentioned methods also have a major limitation as they break momentum and/or energy conservation (sometimes even particle conservation) making the description of realistic thermalization processes at best unreliable.…”