The magnetic order in antiferromagnetic materials is hard to control with external magnetic fields. Using X-ray Magnetic Linear Dichroism microscopy, we show that staggered effective fields generated by electrical current can induce modification of the antiferromagnetic domain structure in microdevices fabricated from a tetragonal CuMnAs thin film. A clear correlation between the average domain orientation and the anisotropy of the electrical resistance is demonstrated, with both showing reproducible switching in response to orthogonally applied current pulses. However, the behavior is inhomogeneous at the submicron level, highlighting the complex nature of the switching process in multi-domain antiferromagnetic films.Antiferromagnetic (AF) materials are of increasing interest both for fundamental physics and applications. Recent advances in detecting and manipulating AF order electrically have opened up new prospects for these materials in basic and applied spintronics research [1][2][3][4][5][6][7]. Of particular interest is the Néel order spin-orbit torque (NSOT) [6], recently demonstrated in the collinear AF CuMnAs [7], where a current-induced local spin polarization can exert a rotation of the magnetic sublattices. NSOT is closely analogous to the spin-orbit torque in ferromagnets with broken inversion symmetry, in which electrical currents induce effective magnetic fields that can be used to switch the magnetization direction [8,9]. The tetragonal CuMnAs lattice [10] is inversion symmetric, so that zero net spin polarization is generated by a uniform electric current. However, its Mn spin sublattices form inversion partners, resulting in local effective fields of opposite sign on the AF-coupled Mn sites [6,11]. These staggered current-induced fields can be large enough to cause a non-volatile rotation of the AF spin axis [7].Current-induced rotations of AF moments can be detected electrically using anisotropic magnetoresistance (AMR), a dependence on the relative orientation of the current and spin axes which is present in both ferromagnetic and AF materials [12][13][14][15]. This provides only spatially averaged information over the probed area of the device, which may be several microns or larger. PhotoEmission Electron Microscopy (PEEM), with contrast enabled by X-ray Magnetic Linear Dichroism (XMLD), provides direct imaging of AF domains with better than 100 nm resolution [16]. Based on differences in absorption of x-rays with linear polarization, XMLD-PEEM has offered valuable insights into the microscopic magnetic properties of AF films [17] and ferromagnet / AF interfaces [18,19]. The measured intensity varies as I 0 + I 2 cos 2 α, where α is the angle between the x-ray polarization and the spin axis [20], so is equally present for AF and FM materials, similar to AMR. The XMLD amplitude given by I 2 also depends on the orientation of the x-ray polarization with respect to the crystalline axes [21,22], and the signal is sensitive to domains within the top few nanometers of the surface.Here, we combin...

The bias voltage applied to a weakly coupled n-doped GaAs/AlAs superlattice increases the amplitude of the coherent hypersound oscillations generated by a femtosecond optical pulse. This bias-induced amplitude increase and experimentally observed spectral narrowing of the superlattice phonon mode with a frequency 441 GHz provides the evidence for hypersound amplification by stimulated emission of phonons in a system where the inversion of the electron populations for phonon-assisted transitions exists.

Van der Waals (vdW) layered crystals and heterostructures have attracted substantial interest for potential applications in a wide range of emerging technologies. An important, but often overlooked, consideration in the development of implementable devices is phonon transport through the structure interfaces. Here we report on the interface properties of exfoliated InSe on a sapphire substrate. We use a picosecond acoustic technique to probe the phonon resonances in the InSe vdW layered crystal. Analysis of the nanomechanics indicates that the InSe is mechanically decoupled from the substrate and thus presents an elastically imperfect interface. A high degree of phonon isolation at the interface points toward applications in thermoelectric devices, or the inclusion of an acoustic transition layer in device design. These findings demonstrate basic properties of layered structures and so illustrate the usefulness of nanomechanical probing in nanolayer/nanolayer or nanolayer/substrate interface tuning in vdW heterostructures.

Voltage controlled modification of the magnetocrystalline anisotropy in a hybrid piezoelectric/ferromagnet device has been studied using Photoemission Electron Microscopy with X-ray magnetic circular dichroism as the contrast mechanism. The experimental results demonstrate that the large magnetostriction of the epitaxial Fe81Ga19 layer enables significant modification of the domain pattern in laterally confined disc structures. In addition, micromagnetic simulations demonstrate that the strain induced modification of the magnetic anisotropy allows for voltage tuneability of the natural resonance of both the confined spin wave modes and the vortex motion. These results demonstrate the possibility for using voltage induced strain in low-power voltage tuneable magnetic microwave oscillators.

A coherent phonon mode with frequency corresponding to the first mini Brillouin-zone edge stop gap is observed in ultrafast pump-probe measurements on a doped semiconductor superlattice structure. It is proposed that the optical detection of the mode is facilitated by interactions with the free carriers present in the superlattice.