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

Zuanming Jin, Jugeng Li, Wenjie Zhang, Chenyang Guo, Caihua Wan, Xiufeng Han, Zhenxiang Cheng, Chao Zhang, Alexey V. Balakin, Alexander P. Shkurinov, Yan Peng, Guohong Ma, Yiming Zhu, Jianquan Yao, and Songlin Zhuang

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.14.014032

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.

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Abstract-Terahertz Emission on the Surface of a van der Waals Magnet CrSiTe3

Peng Suo, Wei Xia, Wenjie Zhang, Xiaoqing Zhu, Jibo Fu,  Xian Lin, Zuanming Jin, Weimin Liu, Yanfeng Guo, Guohong Ma

https://onlinelibrary.wiley.com/doi/abs/10.1002/lpor.202000025

The van der Waals magnet CrSiTe3 (CST) has captured immense interest because it is capable of retaining the long‐range ferromagnetic order even in its monolayer form, thus offering potential use in spintronic devices. Bulk CST crystal has inversion symmetry that is broken on the crystal surface. Here, by employing ultrafast terahertz (THz) emission spectroscopy and time resolved THz spectroscopy, the THz emission of the CST crystal is investigated, which shows a strong THz emission from the crystal surface under femtosecond (fs) pulse excitation at 800 nm. Theoretical analysis based on space symmetry of CST suggests the dominant role of shift current occurring on the surface with a thickness of a few quintuple layers in producing the THz emission, consistent with the experimental observation that the emitted THz amplitude strongly depends on the azimuthal and pumping polarization angles. This study offers a new efficient THz emitter as well as a better understanding of the nonlinear optical response of CST. It hopefully will open a window toward the investigation on the nonlinear optical response in the mono/few‐layer van der Waals crystals with low‐dimensional magnetism.

Abstract-Influence of Oxygen Adsorption on the Terahertz Conductivity Spectroscopy of CVD-Grown MoS2 Thin Flims

Xing Xiao, Litao Zhao, Zeyu Zhang, Xian Lin, Yang Yu, Zuanming Jin, Guohong Ma,  Jianquan Yao

https://www.osapublishing.org/abstract.cfm?uri=ISUPTW-2018-ThC4

By employing the time-resolved terahertz spectroscopy, we have investigated the dynamical photoconductivity response of MoS2 laminate in nitrogen, dry air and oxygen, the photoconductivity of MoS2 is dramatically altered by the adsorption of oxygen.

© 2018 OSA

Abstract-Terahertz time-domain spectroscopy for magnonics and magnetotransport

Zuanming Jin, Xiumei Liu, Shunnong Zhang, Wanying Zhao, Xian Lin, Zongzhi Zhang, Chao Jin, Shixun Cao, Zhenxiang Cheng, Guohong Ma, Jianquan Yao,

https://www.osapublishing.org/abstract.cfm?uri=ISUPTW-2018-ThD2

Terahertz (THz) time-domain spectroscopy can be used to investigate the spintronic effects, such as low-energy magnons and magnetotransports, in the ultrafast operation regime, sub-picosecond time scale and/or terahertz frequency range.

© 2018 OSA

Abstract-Photoinduced terahertz radiation and negative conductivity dynamics in Heusler alloy Co2MnSn film

Shunnong Zhang, Zuanming Jin, Xiumei Liu, Wanying Zhao, Xian Lin, Chao Jing, and Guohong Ma

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-16-3080&origin=search

We report the broadband terahertz (THz) radiation in ferromagnetic half-metallic Heusler alloy Co2MnSn${\mathrm{Co}}_2\mathrm{MnSn}$ thin film upon the irradiation of a femtosecond laser pulse at room temperature. The magnetic-, sample symmetry-, and pump fluence-dependent THz emission reveals that the THz radiation is originated from the magnetic-dipole radiation, i.e., the light-induced subpicosecond demagnetization. In addition, by optical pump-THz probe spectroscopy, we found that the photoexcited increase of the scattering rate of hot carriers thereby leads to the photoinduced negative THz conductivity in Co2MnSn${\mathrm{Co}}_2\mathrm{MnSn}$ thin film.

© 2017 Optical Society of America

Abstract-Switchable metamaterial for enhancing and localizing electromagnetic field at terahertz band

Junxing Liu, Kailin Zhang, Xiankuan Liu, Zeyu Zhang, Zuanming Jin, Xiaoyong He, and Guohong Ma

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-13-13944

In this article, a novel metamaterial is designed aimed at generating a single electromagnetic hot spot, in order to realize the localization of the incident electromagnetic field at terahertz band, and this kind of metastructure is an ideal candidate for many research fields such as spintronics, nonlinear magnetic response, near-field optics, and optical antenna, etc. The specially tailored metamaterial takes the shape of diabolo with a metal triangle pair connected by a cubic gallium arsenide (GaAs) gap. We demonstrated by simulation that both electric- and magnetic-field of incident THz pulse can be confined in the small GaAs gap when a synchronized femtosecond laser pulse is illuminated. The numerical simulation results show that 2 orders of magnitude of field enhancement can be obtained for a 1-by-1 μm GaAs gap, and the field enhancement factor can also be further improved by tailoring the GaAs gap down to nanometer scale.

© 2017 Optical Society of America

Abstract-Terahertz broadband modulation in a biased BiFeO3/Si heterojunction

Xiankuan Liu, Zeyu Zhang, Xian Lin, Kailin Zhang, Zuanming Jin, Zhenxiang Cheng, and Guohong Ma

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-23-26618

A new terahertz (THz) modulator based on bias-driven carrier conductivity change in a heterojunction was proposed. BiFeO3 film and silicon were selected as building blocks for fabricating the THz modulator. THz nonlinear transmission as a function of bias voltage was studied systematically. THz peak transmission as a function of bias shows a similar tendency as the current-voltage response of the heterojunction: the forward bias leads to the exponential enhancement of THz transmission, and in contrast, the reverse bias shows no observable changes in THz transmission. The modulation depth and modulation bandwidth of THz pulse can reach up to 42% and 1.0 THz with forward bias of 4.8 V, respectively. The observed bias dependent THz transmission in the BFO/Si heterojunction is well-interpreted by the proposed model: the diffused carriers across the heterojunction are localized in BFO thin film with applied forward bias. Our finding provides great potential for applications in designing all electrical broadband THz modulators.

© 2016 Optical Society of America

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Abstract-Resolving the spin reorientation and crystal-field transitions in TmFeO3 with terahertz transient

• Kailin Zhang
• , Kai Xu
• , Xiumei Liu
• , Zeyu Zhang
• , Zuanming Jin
• , Xian Lin
• , Bo Li
• , Shixun Cao
•  &Guohong Ma

http://www.nature.com/articles/srep23648
Rare earth orthoferrites (RFeO3) exhibit abundant physical properties such as, weak macroscopic magnetization, spin reorientation transition, and magneto-optical effect, especially the terahertz magnetic response, have received lots of attention in recent years. In this work, quasi-ferromagnetic (FM) and quasi-antiferromagnetic (AFM) modes arising from Fe sublattice of TmFeO3 single crystal are characterized in a temperature range from 40 to 300 K, by using terahertz time-domain spectroscopy (THz-TDS). The magnetic anisotropy constants in ac-plane are estimated according to the temperature-dependent resonant frequencies of both FM and AFM modes. Here, we further observe the broad-band absorptions centered ~0.52, ~0.61, and ~1.15 THz below 110 K, which are reasonably assigned to a series of crystal-field transitions (R modes) of ground multiplets (6H3) of Tm3+ ions. Specially, our finding reveals that the spin reorientation transition at a temperature interval from 93 to 85 K is driven by magnetic anisotropy, however, which plays negligible role on the electronic transitions of Tm ions in the absence of applied magnetic fields.

Abstract-Terahertz probes of magnetic field induced spin reorientation in YFeO3 single crystal

Xian Lin¹, Junjie Jiang¹, Zuanming Jin^1,2, Dongyang Wang³, Zhen Tian³,Jiaguang Han³, Zhenxiang Cheng^1,4 and Guohong Ma^1,a)


a) Author to whom correspondence should be addressed. Electronic mail: ghma@staff.shu.edu.cn
Appl. Phys. Lett. 106, 092403 (2015); http://dx.doi.org/10.1063/1.4913998
http://scitation.aip.org/content/aip/journal/apl/106/9/10.1063/1.4913998

Using the terahertz time-domain spectroscopy, we demonstrate the spin reorientation of a canted antiferromagnetic YFeO3 single crystal, by evaluating the temperature and magnetic field dependence of resonant frequency and amplitude for the quasi-ferromagnetic (FM) and quasi-antiferromagnetic modes (AFM), a deeper insight into the dynamics of spin reorientation in rare-earth orthoferrites is established. Due to the absence of 4f-electrons in Y ion, the spin reorientation of Fe sublattices can only be induced by the applied magnetic field, rather than temperature. In agreement with the theoretical predication, the frequency of FM mode decreases with magnetic field. In addition, an obvious step of spin reorientation phase transition occurs with a relatively large applied magnetic field of 4 T. By comparison with the family members of RFeO3 (R = Y³⁺ or rare-earth ions), our results suggest that the chosen of R would tailor the dynamical rotation properties of Fe ions, leading to the designable spin switching in the orthoferrite antiferromagnetic systems.

Abstract-Complementary terahertz absorption and inelastic neutron study of the dynamic anisotropy contribution to zone-center spin waves in a canted antiferromagnet NdFeO3

Evan Constable, D. L. Cortie, Joseph Horvat, R. A. Lewis, Zhenxiang Cheng, Guochu Deng, Shixun Cao, Shujuan Yuan, and Guohong Ma
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.054413

We employ a combination of pulsed- and continuous-wave polarized terahertz spectroscopy techniques to probe temperature-dependent spin waves in the antiferromagnet NdFeO3. Our optical data span 1.6–467 K and reveal a conspicuous spin reorientation between 110 and 170 K, during which the lower-energy mode softens completely. Complementary inelastic neutron scattering reveals that the frequencies of the optically excited spin waves are consistent with a temperature-variable spin gap in the low-energy spin-wave dispersion of NdFeO3. The result links the temperature dependence of the spin waves to a dynamic in-plane anisotropy. The magnetic anisotropy is calculated based on the results of the optical measurements. The change observed in the anisotropy energy along the a and c crystal axes suggests that the spin reorientation evident in NdFeO3 is driven by temperature-dependent in-plane anisotropy.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.054413

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Abstract-Evolution of terahertz conductivity in ZnSe nanocrystal investigated with optical-pump terahertz-probe spectroscopy

Gaofang Li, 

Xin Xue, 

Xian Lin, 

Sannan Yuan, 

Naiyun Tang, 

Fenghong Chu, 

Haoyang Cui, 

Guohong Ma

http://link.springer.com/article/10.1007%2Fs00339-014-8481-5

Ultrafast carrier dynamics and terahertz conductivity of ZnSe nanocrystal are investigated by means of the optical-pump terahertz-probe spectroscopy at room temperature. With the laser pulse excitation at 400 nm, the negative transmission of terahertz pulse shows an ultrafast rising followed by a biexponential recovery. The fast decay component with time constant of 5 ps is dominated by the photocarriers backscattering at interfaces of ZnSe nanoparticles, and the slow one with time constant longer than 1 ns can be assigned to the carrier recombination from band-to-band transition. The evolution of conductivity with time demonstrates that this kind of nanostructure is a good candidate for fabricating ultrafast terahertz switching.