Ultrafast terahertz magnetometry

Abstract

A material's magnetic state and its dynamics are of great fundamental research interest and are also at the core of a wide plethora of modern technologies. However, reliable access to magnetization dynamics in materials and devices on the technologically relevant ultrafast timescale, and under realistic device-operation conditions, remains a challenge. Here, we demonstrate a method of ultrafast terahertz (THz) magnetometry, which gives direct access to the (sub-)picosecond magnetization dynamics even in encapsulated materials or devices in a contact-free fashion, in a fully calibrated manner, and under ambient conditions. As a showcase for this powerful method, we measure the ultrafast magnetization dynamics in a laser-excited encapsulated iron film. Our measurements reveal and disentangle distinct contributions originating from (i) incoherent hot-magnon-driven magnetization quenching and (ii) coherent acoustically-driven modulation of the exchange interaction in iron, paving the way to technologies utilizing ultrafast heat-free control of magnetism. High sensitivity and relative ease of experimental arrangement highlight the promise of ultrafast THz magnetometry for both fundamental studies and the technological applications of magnetism.

Terahertz Spin‐to‐Charge Conversion by Interfacial Skew Scattering in Metallic Bilayers

“…The same argument applies to a contribution to the THz charge current from ultrafast demagnetization. [ 51 ]…”

Temperature‐Dependent Terahertz Emission from Co/Mn2Au Spintronic Bilayers

“…[ 39,40 ] Such a response is analogous to a straightforward Hertzian dipole leading to a purely THz ultrafast magnetic dipole radiation (UMDR), E M ( t ). [ 41 ] On the other hand, during the excited hot carriers diffuse and relax, the majority‐spin electrons are sp ‐like band electrons and persist for a longer time at high energies than the minority‐spin electrons in d band, [ 35 ] resulting in an ultrafast spin‐polarized current. [ 30,31 ] As the spin diffusion length of the Co layer (38 ± 12 nm) is much larger than the thickness of Co layer (3 nm), [ 42 ] the spin‐polarized current j s can penetrate superdiffusively into the adjacent AFM layers.…”

“…First, the thickness of Co layer used in this work was chosen to be 3 nm, which ensures a virtually uniform pump intensity distribution within the Co film. [ 41 ] Thus, the effect related to hot electron diffusion within the Co film can be safely excluded. Second, the normal‐incidence excitation scheme can greatly eliminate the contribution of magnetically enhanced surface nonlinearity to the THz emission.…”

Terahertz chiral sensing and magneto-optical enhancement for ferromagnetic nanofluids in the chiral metasurface

“…For further development of the THz application system, there is a high demand for efficient devices for sensing and manipulating THz waves in their amplitude, phase, and polarization [5][6][7][8] . The unique magnetic anisotropy, nonreciprocity, and magnetic tunability of magneto-optical material make them play an irreplaceable role in the isolator, magneto-optical polarization convertor, modulator, and magnetic field sensor [9][10][11][12][13][14] . However, researches on the magnetic properties of THz waves lag seriously, so it is necessary to fill the "terahertz gap" by not only electrical but also magnetic means.…”