Nonlinear spin control by terahertz-driven anisotropy fields

Abstract

Future information technologies, such as ultrafast data recording, quantum computation or spintronics, call for ever faster spin control by light [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] . Intense terahertz pulses can couple to spins on the intrinsic energy scale of magnetic excitations 5,11 . Here, we explore a novel electric dipole-mediated mechanism of nonlinear terahertz-spin coupling that is much stronger than linear Zeeman coupling to the terahertz magnetic field 5,10 . Using the prototypical antiferromagnet thulium orthoferrite (TmFeO 3 ), we demonstrate that resonant terahertz pumping of electronic orbital transitions modifies the magnetic anisotropy for ordered Fe 3+ spins and triggers large-amplitude coherent spin oscillations. This mechanism is inherently nonlinear, it can be tailored by spectral shaping of the terahertz waveforms and its efficiency outperforms the Zeeman torque by an order of magnitude. Because orbital states govern the magnetic anisotropy in all transition-metal oxides, the demonstrated control scheme is expected to be applicable to many magnetic materials.Ultrafast magnetization control has become a key goal of modern photonics, with a broad variety of successful concepts emerging at a fast pace. Examples include light-induced spin reorientation in canted antiferromagnets 3 , vectorial control of magnetization by light 6 , photoinduced antiferromagnet-ferromagnet phase transitions 9 , optical modification of the exchange energy 4,14 and driving spin precessions via nonlinear magneto-phononic coupling 7,16 . Despite this remarkable progress, most of the photon energy in all known concepts using visible and near-infrared light is inactive with respect to the light-spin interaction, and avoiding dissipation of large excess energies requires special care.In contrast, intense electromagnetic pulses at terahertz frequencies may interface spin dynamics directly on their intrinsic energy scales 5,11 . The magnetic field component of few-cycle terahertz pulses has been used to coherently control magnons in the electronic ground state by direct Zeeman interaction 5,11 . Because magnetic dipole coupling is typically weak, however, terahertz-driven spin excitation has been confined to the linear response regime. Massive nonlinearities, such as terahertz-induced phase transitions 17,18 and terahertz lightwave electronics [19][20][21][22]

Interplay of Fe and Tm moments through the spin-reorientation transition inTmFeO3

“…The focus has been on ultrafast manipulation of magnetic order, achieved by exciting the system with ultrashort and intense optical pulses [6][7][8]. It has indeed been shown that a significant spin reorientation can be obtained on ultrafast time scales in TmFeO 3 [6].…”

Ultra‐Fast Control of Magnetic Relaxation in a Periodically Driven Hubbard Model

“…The dynamics for t > t 1 is thus slower than that for t < t 1 by a factor of 2, in addition to the change of sign, resulting in an almost-complete reversal of both the magnetic order parameter and the double occupation after an evolution of length 2t 1 . The reversal is not perfect due to the higher-order terms in Hamiltonian (13). However our results show that it is possible to almost entirely re-magnetize a system whose order parameter has been strongly suppressed on a ultra-fast time scale.…”

“…Here we use a similar idea to induce a dynamics reversal on much shorter time scales ν 0 t < 8, but with a sudden quench of the amplitude of a l = 1 resonant driving designed to invert the sign of the effective Hamiltonian (13). The scheme consists of two stages, starting from a Néel state, and leading to the results depicted in Fig.…”

Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

“…The thickness parameters of the nominally 0. 6 . These parameters were kept constant during the THz frequency calibration procedure.…”

“…The dielectric function of a material provides access to quantitative determination for many fundamental physical properties, for example, static and high-frequency dielectric permittivity, phonon modes, free charge carrier properties, band-to-band transition energies and life time broadening parameters. Expanding the accessible spectral range of spectroscopic ellipsometry to longer wavelengths, namely into the terahertz (THz) region, provides access to information about soft modes [4], DNA methylation [5], spin oscillations [6], antiferromagnetic resonances [7], ferroelectric domains [8] and free charge carrier oscillations [9], for example.…”