Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(0 0 1) interfaces

Abstract

We demonstrate a novel method for the excitation of sizable magneto-optical effects in Au by means of the laser-induced injection of hot spin-polarized electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy-and spin-dependent electron transmittance of Fe/Au interface which acts as a spin filter for non-thermalized electrons optically excited in Fe. We show that after crossing the interface, majority electrons propagate through the Au layer with the velocity on the order of 1 nm/fs (close to the Fermi velocity) and the decay length on the order of 100 nm. Featuring ultrafast functionality and requiring no strong external magnetic fields, spin injection results in a distinct magneto-optical response of Au. We develop a formalism based on the phase of the transient complex MOKE response and demonstrate its robustness in a plethora of experimental and theoretical MOKE studies on Au, including our ab initio calculations. Our work introduces a flexible tool to manipulate magneto-optical properties of metals on the femtosecond timescale that holds high potential for active magneto-photonics, plasmonics, and spintronics. arXiv:1810.12237v1 [cond-mat.mes-hall]

Detection of femtosecond spin injection into a thin gold layer by time and spin resolved photoemission

“…Recent time-resolved experiments 17 – 19 have demonstrated the detection of spin injection using the linear, complex and second harmonic magneto-optic Kerr effect (SHMOKE). The authors of 18 , 19 observed the generation of non-thermal spin transport, as predicted theoretically 20 – 22 . SHMOKE is sensitive to spin polarization at interfaces and is therefore well suited for observing transport effects.…”

“…The sign of the injected spin polarization for delay times fs is consistent with several theoretical predictions 20 – 22 , 36 . However, for delay times fs, several authors observed the injection of minority spins into the gold layer 18 , 21 . This negative polarization shortly after the excitation pulse is not present in our data.…”

Generation of exchange magnons in thin ferromagnetic films by ultrashort acoustic pulses

“…By adding the damping term and the explicit expression for A (n) 32 from Eq. (27) we arrive at the most important analytical equation in this paper:…”

“…Depending on a mechanism, magnetization dynamics induced by a femtosecond laser pulse can be sorted into the following categories: (i) thermal effects [3,13], (ii) magnetooptical effects [22], (iii) magnetoacoustic effects [15,18,19,[23][24][25][26][27] and (iv) spin transfer torque [28][29][30][31]. Despite of the facts that the spin transfer torque is an efficient mechanism to drive coherent magnetization dynamics in ferromagnet through ultrashort pulses of spinpolarized electrons propagating in noble metals for several tens of nanometers before they lose their spin polarization [32], acoustic pulses can propagate over much larger distances before they vanish. Picosecond acoustic pulses generated by femtosecond laser excitations [25,[33][34][35] can drive the small-angle precession of ferromagnetic resonance (FMR) in various ferromagnetic samples [15,19,23,24].…”

Compact setup for spin-, time-, and angle-resolved photoemission spectroscopy

“…An example of this is the qualitative discrepancy between the results obtained by different optical techniques in spin-transport experiments. 1 The desire to gain insight into the spin-resolved band structure has driven the development of detection schemes that allow the recording of the emitted electron energy, momentum, and spin.…”