Magnetic Modulation of Terahertz Waves via Spin-Polarized Electron Tunneling Based on Magnetic Tunnel Junctions

Abstract

© 2020 American Physical Society. Magnetic tunnel junctions (MTJs) are a key technology in modern spintronics because they are the basis of read-heads of modern hard disk drives, nonvolatile magnetic random access memories, and sensor applications. In this paper, we demonstrate that tunneling magnetoresistance can influence terahertz (THz) wave propagation through a MTJ. In particular, various magnetic configurations between parallel state and antiparallel state of the magnetizations of the ferromagnetic layers in the MTJ have the effect of changing the conductivity, making a functional modulation of the propagating THz electromagnetic fields. Operating in the THz frequency range, a maximal modulation depth of 60% is reached for the parallel state of the MTJ with a thickness of 77.45 nm, using a magnetic field as low as 30 mT. The THz conductivity spectrum of the MTJ is governed by spin-dependent electron tunneling. It is anticipated that the MTJ device and its tunability scheme will have many potential applications in THz magnetic modulators, filtering, and sensing.

Generation of Tunable Terahertz Waves from Tailored Versatile Spintronic Meta-Antenna Arrays

“…These results can be attributed to a geometric-confinement model from the perspective of Figure a, which considers the dynamics and the interplay of the transverse charge current j c , as well as the transient metamaterial-induced charges Q i and current density J i . According to the research studies of Liu and Jin, the electric-field component E x of the terahertz wave is proportional to the magnitude of the total current density, which can be described as E x ( w ) = k x ( w ) J x ( w ) = k x ( w ) J c ( w ) cos nobreak0em.25em⁡ α normals where k x is a constant determined by the conductivity of the metal layer and the metamaterial geometry. On the other hand, the electric-field component E y not only consists of the y -axis component of j c but also the metamaterial-induced counteractive current J i E y ( w ) = k y ( w ) J y ( w ) = k y ( w ) false( J c ( w ) sin nobreak0em.25em⁡ α normals − J i false) where J i derives from t...…”

“…These results can be attributed to a geometric-confinement model from the perspective of Figure 2a, 13 which considers the dynamics and the interplay of the transverse charge current j c , as well as the transient metamaterial-induced charges Q i and current density J i . According to the research studies of Liu 13 and Jin, 12 the electric-field component E x of the terahertz wave is proportional to the magnitude of the total current density, which can be described as…”

“…A ferromagnetic heterostructure-based spintronic terahertz emitter (STE) that generates broadband terahertz (THz) pulses at room temperature has the advantages of low cost, large bandwidth, and high scalability. − As a result, many spintronic terahertz devices have been developed and investigated within the terahertz community. − Recently, the rapid expansion of THz application has put forward higher and more diverse demands on ferromagnetic heterostructures, , such as the enhancement of emitted power, modulation of radiated terahertz pulses, and ellipticity generation. Methods including electric field, magnetic field, azimuth angle, and antenna structure are applied in the enhancement and modulation of spintronic terahertz waves.…”

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

“…As the propagation of terahertz (THz) waves in materials is mainly affected by the motion of the electrons, it provides the most direct way to probe the magneto-transport properties on an ultrafast time scale. Over the past years, THz time-domain spectroscopy (THz-TDS) has provided the opportunity for not only investigating biomedical systems [ 19 , 20 ], but also uncovering the spin dynamics in both antiferromagnetic [ 21 , 22 , 23 , 24 , 25 ] and ferromagnetic materials [ 26 , 27 , 28 , 29 , 30 ]. Furthermore, in contrast to the TR-MOKE method, THz emission spectroscopy does not rely on the magneto-optical response and has been used as a fingerprint identification of the ultrafast demagnetization [ 31 , 32 ], inverse spin Hall effect (ISHE) [ 33 , 34 , 35 ], inverse spin–orbit torque [ 36 ], inverse Rashba–Edelstein effect (IREE) [ 37 , 38 , 39 ], and anomalous Hall effect (AHE) [ 40 ].…”

Spintronic terahertz emitters exploiting uniaxial magnetic anisotropy for field-free emission and polarization control

“…This could widen their practical application, for example in THz magneto-optical spectroscopy of field sensitive materials such as ferrofluids, 27-29 metasurfaces, 30 and magnetic tunnel junctions. 31 The removal of the requirement for operation within a magnetic field could also facilitate the scaling up of spintronic structures to produce large-area, high-field THz emitters. Applying…”