Sub-100-ps dynamics of the anomalous Hall effect at terahertz frequencies

Abstract

We report about the anomalous Hall effect in 4f 3d metallic alloys measured using terahertz time-domain spectroscopy. The strength of the observed terahertz spin-dependent transport phenomenon is in good agreement with expectations based on electronic transport measurements. Employing this effect, we succeeded to reveal ultrafast dynamics of the anomalous Hall effect which accompanies the sub-100 picosecond optically induced magnetization reversal in a GdFeCo alloy. The experiments demonstrate the ability to control currents at terahertz frequencies in spintronic devices magnetically and ultrafast.To develop ultrafast spintronics logic protocols for high-speed data processing, one has to find a way to control and detect the spin-dependent transport ultrafast. The conventional approach to study magnetotransport is based on the application of an electrical voltage to a sample and the detection of the subsequent electrical current via electrodes. However, making electrical contacts that transfer a picosecond (ps) short signal without substantial distortions and broadening is rather challenging [1]. An elegant solution for the problem of ultrafast conductivity measurements can be found by using freely propagating terahertz (THz) waves.To date, THz spectroscopy has been used to study magnetotransport in a large diversity of materials [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. However, only a few of these studies have been dedicated to magnetically ordered materials and in none of these materials the magnetization could be reversed ultrafast. To reveal sub-100 ps dynamics in the anomalous Hall effect, we have chosen ferrimagnetic Gdx(FeCo)1-x thin films, as they are expected to show a significant anomalous Hall effect [18][19][20], and are known for their ultrafast all-optical magnetization reversal [21][22][23][24][25][26].The studied Gdx(Fe0.875Co0.125)1-x samples are 20 nm thick amorphous films, which have adjacent 5 nm SiN protecting layers and are deposited using magnetron sputtering. These samples have a ferrimagnetic ordering and an out-of-plane magnetic anisotropy in the studied Gd concentration range (0.2<x<0.3), with the magnetization being dominated by the FeCo magnetic sublattice at room temperature. At lower temperatures the magnetization of the Gd magnetic sublattice may start to dominate. The temperature at which this happens is known as the magnetization compensation temperature, the value of which can be tuned with the concentration of Gd.Our experimental setup consists of a THz time domain spectrometer designed to allow simultaneous excitation of the sample with an intense optical pump and detecting changes in a

Spin-photo-currents generated by femtosecond laser pulses in a ferrimagnetic GdFeCo/Pt bilayer

“…2(d) shows that the measured magneto-optical Faraday effect in the THz spectral range for this sample is characterized by an abrupt change near T comp as measured with the VSM, similar to what we show in Ref. 15. Since both the THz emission and THz Faraday rotation are measured in the same setup, we can exclude the influence of errors in the temperature determination.…”

Terahertz Emission from Anomalous Hall Effect in a Single-Layer Ferromagnet

“…In summary, we have demonstrated an alternative mechanism for generating THz emission from ultrathin FM layer via the AHE, though the presence of AHE in the THz regime has been reported before [39][40][41]. The process involves generation of backflow super-diffusive current at the FM/dielectric interfaces and subsequent conversion of the charge current to transverse current via AHE, and thereby generating the THz radiation.…”

Giant magneto-optical responses in magnetic Weyl semimetal Co3Sn2S2

“…The Faraday rotation observed at zero field, which exceeds 160 mrad (3.8 mrad/nm), is larger than that of the conventional ferromagnets represented by the archetypal MO material Bi:YIG with 0.77 mrad/nm 25 , 26 , 32 – 35 (Fig. 4b ).…”