Temperature‐Dependent Terahertz Emission from Co/Mn₂Au Spintronic Bilayers

Abstract

Recently, ferromagnetic/nonmagnetic heavy metal heterostructures have been intensively investigated as terahertz (THz) emitters. The interconversion of spin‐to‐charge dynamics plays a central role for efficient emission of THz electromagnetic pulses. However, a direct observation of spin–charge interconversion in antiferromagnetic (AFM) materials occurring on the sub‐picosecond time scale remains a challenge. Herein, the magnetic‐field‐, pump‐fluence‐, and polarization‐dependent THz emission behaviors by a femtosecond optical pump in cobalt (Co)/Mn2Au nanometer heterostructure are experimentally investigated. The Co/Mn2Au bilayer generates sizable THz signals, whereas the Mn2Au/Pt bilayer does not show any THz emission. In addition, the thickness‐ and temperature‐dependent THz emission measurements indicate a direct relation between the THz amplitude and the conductivity of AFM Mn2Au layer. The results obtained will not only promote the fundamental understanding of ultrafast spin–charge interconversion in Co/Mn2Au heterostructures, but also provide a possibility of spectroscopic‐based spin current detector at THz‐frequency range.

Cascaded Amplification and Manipulation of Terahertz Emission by Flexible Spintronic Heterostructures

“…Strategies for the transient spin-charge conversion dynamics in terms of materials, thicknesses, structures, and interfaces have been a topic of intense research because of the potential applications of THz generation and modulation. [40][41][42][43][44][45][46] In comparison with the available fs laser-based THz sources, such as optical rectification nonlinear crystals and photoconductive switching, the spintronic THz emitter (STE) is cost-effective, easy to use, robust and has broad bandwidth. The THz emission efficiency of STE has been so far improved to reach the same level of millimeter-thick ZnTe crystal.…”

Inverse Altermagnetic Spin Splitting Effect‐Induced Terahertz Emission in RuO2

“…We turn first toward the question of why the amplitude of THz signal of the RuO 2 (100)/Py sample is smaller than that of the RuO 2 (110)/Py sample. Notably, the amplitude of the THz field E THz in ferromagnet/antiferromagnet heterojunction as a function of the antiferromagnetic thickness is given by: [17,18]…”

“…We turn first toward the question of why the amplitude of THz signal of the RuO 2 (100)/Py sample is smaller than that of the RuO 2 (110)/Py sample. Notably, the amplitude of the THz field E THz in ferromagnet/antiferromagnet heterojunction as a function of the antiferromagnetic thickness is given by: [ 17,18 ] $$$$\begin{eqnarray}{E}_{{\rm{THz}}}\left( d \right) \propto \;{\gamma }_{{\rm{AF}}}\;{\lambda }_{{\rm{rel}}}{A \over {{d}_{{\rm{tot}}}}}{{{\rm{tanh}}\left( {{d}_{{\rm{AF}}}/2{\lambda }_{{\rm{rel}}}} \right)} \over {{n}_{{\rm{air}}} + {n}_{{\rm{sub}}} + {Z}_0\mathop \smallint \nolimits_0^d {\rm{d}}z\sigma \left( z \right)}}\end{eqnarray}$$$$where γ AF and λ rel are the spin Hall angle and the spin diffusion length of the antiferromagnet, respectively. d tot and d AF represent respectively the thickness of the total film and the antiferromagnetic film.…”

“…[11][12][13][14] The antiferromagnet (AFM), with its specific magnetic structure and unique characteristics, has been proposed to replace the heavy metals serving as an effective spin sink and make the FM/AFM bilayer a promising candidate for the THz emitter. [15][16][17][18] The crystal structure and Néel vector of AFM provide a unique opportunity for tailoring the THz emission. [19,20] Recently, the altermagnetic materials with collinear compensated magnetic order and crystal rotation symmetry have been demonstrated to show strong time-reversal (T) symmetrybreaking responses, [21][22][23][24][25][26] such as the anomalous Hall effect [27][28][29] and the non-trivial spin current generation, [30][31][32][33][34] which are ascribed to the nonrelativistic altermagnetic spin splitting effect (ASSE).…”

“…[ 11–14 ] The antiferromagnet (AFM), with its specific magnetic structure and unique characteristics, has been proposed to replace the heavy metals serving as an effective spin sink and make the FM/AFM bilayer a promising candidate for the THz emitter. [ 15–18 ] The crystal structure and Néel vector of AFM provide a unique opportunity for tailoring the THz emission. [ 19,20 ]…”