Terahertz spintronic magnetometer (TSM)

Abstract

A ferromagnetic metal consists of localized electrons and conduction electrons coupled through strong exchange interaction. Together, these localized electrons contribute to the magnetization of the system, while conduction electrons lead to the formation of spin and charge current. Femtosecond out of equilibrium photoexcitation of ferromagnetic thin films generates a transient spin current at ultrafast timescales that have opened a route to probe magnetism offered by the conduction electrons. In the presence of a neighboring heavy metal layer, the non-equilibrium spin current is converted into a pulsed charge current and gives rise to terahertz (THz) emission. Here, we propose and demonstrate a tool known as the terahertz spintronic magnetometry. The hysteresis loop obtained by sweeping terahertz (THz) pulse amplitude as a function of the magnetic field is in excellent agreement with the vibrating-sample magnetometer measurements. Furthermore, a modified transfer-matrix method employed to model the THz propagation within the heterostructure theoretically elucidates a linear relationship between the THz pulse amplitude and sample magnetization. The strong correlation, thus, reveals spintronic terahertz emission as an ultrafast magnetometry tool with reliable in-plane magnetization detection, highlighting its technological importance in the characterization of ferromagnetic thin-films through terahertz spintronic emission spectroscopy.

Spintronic emitter of terahertz radiation based on two-dimensional semiconductor tungsten diselenide

“…We have demonstrated in our earlier study [15] that magnetization curves match perfectly the parameters of the THz signal amplitude hysteresis for TbCo/FeCo structures. Similar results were obtained by the authors of [16] for the Co 40 Fe 40 B 20 (1.8 nm)/Pt (2 nm) structure. The matching of parameters of hysteresis curves of the THz signal amplitude and magnetization curves is typical only of metallic spintronic THz emitters where the emission is governed by ISHE.…”

Secondary Spin Current Driven Efficient THz Spintronic Emitters

“…As a result, the heterostructure emits terahertz electric field according to E ( t ) = ∂ j c ( t )/∂ t [ 12–14,42 ] and terahertz pulse amplitude scales with the ultrafast charge current amplitude, given by, $${\bf{E}}_{( t )}^{{{\bf peak}}} \propto $$$${\bf{j}}_{{\bf c}}^{{{\bf peak}}} \propto $$$${\bf{j}}_{{\bf s}}^{{{\bf peak}}}$$. [ 18,43 ] Besides, within the heterostructure, the terahertz field is also produced from minor processes without involving superdiffusion of spin current across the FM/HM interface. The mechanism includes i) ultrafast change in magnetic dipoles, [ 20 ] ii) ultrafast change in electric dipoles, [ 20 ] and iii) back reflection of spins in FM that experience spin‐to‐charge conversion due to anomalous Hall effect.…”

“…[4][5][6][7] At the same time, the spins superdiffuse semi-ballistically, forming direct channels of spin transport between the FM and HM layers. [8][9][10][11] The phenomena have led to the development of a range of applications such as broadband terahertz sources, [12][13][14][15][16] ultrafast spintransfer-torque driven logic devices, [17] terahertz (THz) magnetometry, [18][19][20] spin-resolved electron spectroscopy, [21] ballistic electron emission microscopy, [22] nextgeneration data-processors, [23][24][25][26][27] and ultrafast spin injection in semiconductors and topological insulators. [28][29][30][31][32][33] Theoretical calculations attributed to the superdiffusion predicted the scattering processes within the FM and HM to cause the flow of hot electrons both from the FM to HM and HM to FM, [8,34] leading to enhanced ultrafast demagnetization of FM.…”

Terahertz Emission Spectroscopy of Ultrafast Coupled Spin and Charge Dynamics in Nanometer Ferromagnetic Heterostructures

“…The j tot pulse consists of a positive peak followed by a negative one, which changes sign around 1.4 ps after onset. To gain more insight into our data, j tot is fitted by a current profile [ 58 , 59 ], as follows: where . Here, and are the rise and decay time constants of j i=c,res , respectively.…”