T. T. Gareev

Ultrafast pump-probe imaging reveals that the efficiency of optical excitation of coherent spin waves in epitaxial iron garnet films can be effectively controlled by an external electric field at room temperature. Although a femtosecond laser pulse alone does not excite any pronounced coherent spin oscillations, an electrical gating with the field of 0.5 MV/m dramatically changes the outcome in a laser-induced launching of spin waves. The effect, demonstrated under room-temperature conditions, is estimated to be orders of magnitude larger than in magnetic van der Waals semiconductors observed at 10 K. This electrical gating of laser-induced spin dynamics enriches optomagnonics with a new tool and thus opens up a new avenue in fundamental and applied magnonics research.

The optical pump-probe technique is a common tool for the investigation of ultrafast spin dynamics, which usually utilizes single-diode detection averaging the dynamics over the pumped area. Using an ultrafast imaging technique, we show experimentally that a femtosecond laser pulse with a gradient distribution of intensity efficiently excites strongly inhomogeneous spin dynamics on spatial scales much smaller than the pump spot size. The mechanism responsible for the inhomogeneous distribution is based on temperature gradients and corresponds to a sign change of the torque derivative in different areas of the pump. We argue that the observed phenomenon is general for the systems with competitive magnetic anisotropies. Overlooking this effect in the majority of pump-probe experiments can result in a dramatic underestimate of the lifetime and amplitude of the laser-induced spin dynamics.

Resonant pumping of the electronic f-f transitions in the orbital multiplet of dysprosium ions (Dy^{3+}) in a complex perovskite DyFeO_{3} is shown to impulsively launch THz lattice dynamics corresponding to the B_{2g} phonon mode, which is dominanted by the motion of Dy^{3+} ions. The findings, supported by symmetry analysis and density-functional theory calculations, not only provide a novel route for highly selective excitation of the rare-earth crystal lattices but also establish important relationships between the symmetry of the electronic and lattice excitations in complex oxides.

Controlled generation of coherent spin waves with highest possible frequencies and shortest possible wavelengths is a cornerstone of spintronics and magnonics. Here, using Heisenberg antiferromagnet RbMnF3, we demonstrate that laser-induced THz spin dynamics corresponding to pairs of mutually coherent counter-propagating spin waves with the wavevectors up to the edge of the Brillouin zone cannot be understood in terms of magnetization and antiferromagnetic (Néel) vectors, conventionally used to describe spin waves. Instead, we propose to model such spin dynamics using the spin correlation function. We derive a quantum-mechanical equation of motion for the latter and emphasize that unlike the magnetization and antiferromagnetic vectors the spin correlations in antiferromagnets do not exhibit inertia.

CoPS3 stands out in the family of the van der Waals antiferromagnets XPS3 (X = Mn, Ni, Fe, and Co) due to the unquenched orbital momentum of the magnetic Co2+ ions, which is known to facilitate the coupling of spins to both electromagnetic waves and lattice vibrations. Here, using a time-resolved magneto-optical pump–probe technique, we experimentally study the ultrafast laser-induced dynamics of mutually correlated spins and lattice. It is shown that a femtosecond laser pulse acts as an ultrafast heater and, thus, results in the melting of the antiferromagnetic order. At the same time, the resonant pumping of the 4T1g → 4T2g electronic transition in Co2+ ions effectively changes their orbital momentum, giving rise to a mechanical force that moves the ions in the direction parallel to the orientation of their spins, thus generating a coherent Bg phonon mode at the frequency of about 4.7 THz.

Механизмы магнитоэлектрических эффектов в оксидных мультиферроиках с прафазой перовскита

Néel-type magnetic domain walls locally reduce the symmetry of the crystal and give rise to electric polarization. This type of localized multiferroicity is particularly promising due to the sensibility of the domain wall's internal structure to the magnetic field. In this paper, the magnetic-field-modified electric polarization of the domain wall is considered and compared to the room-temperature giant magnetoelectric effect observed on domain walls in iron garnet films.

Magnetoelectric effects in multiferroics give an opportunity to control intrinsic magnetic ordering with an external electric field. In this paper, we demonstrate the emergence of magnetic domains in the local electric field generated by cantilever tip in the (110)-oriented iron garnet film at room temperature. We show that the in-plane magnetized phase observed in this film enables the nucleation of the magnetic domain with 90°domain walls both at positively and negatively biased tip. The found bipolarity of the effect is in contrast to the unipolar nucleation of a bubble domain in the case of a conventional 180° domain wall. The experimental and theoretical studies reveal the mechanism of electric field generation of the 90° magnetic domain and its dependence on the domain wall's chirality.