12 research outputs found
Terahertz electrical writing speed in an antiferromagnetic memory
The speed of writing of state-of-the-art ferromagnetic memories is physically limited by an intrinsic gigahertz threshold. Recently, realization of memory devices based on antiferromagnets, in which spin directions periodically alternate from one atomic lattice site to the next has moved research in an alternative direction. We experimentally demonstrate at room temperature that the speed of reversible electrical writing in a memory device can be scaled up to terahertz using an antiferromagnet. A current-induced spin-torque mechanism is responsible for the switching in our memory devices throughout the 12-order-of-magnitude range of writing speeds from hertz to terahertz. Our work opens the path toward the development of memory-logic technology reaching the elusive terahertz band
Terahertz probing of anisotropic conductivity and morphology of CuMnAs epitaxial thin films
Antiferromagnetic CuMnAs thin films have attracted attention since the
discovery of the manipulation of their magnetic structure via electrical,
optical, and terahertz pulses of electric fields, enabling convenient
approaches to the switching between magnetoresistive states of the film for the
information storage. However, the magnetic structure and, thus, the efficiency
of the manipulation can be affected by the film morphology and growth defects.
In this study, we investigate the properties of CuMnAs thin films by probing
the defect-related uniaxial anisotropy of electric conductivity by contact-free
terahertz transmission spectroscopy. We show that the terahertz measurements
conveniently detect the conductivity anisotropy, that are consistent with
conventional DC Hall-bar measurements. Moreover, the terahertz technique allows
for considerably finer determination of anisotropy axes and it is less
sensitive to the local film degradation. Thanks to the averaging over a large
detection area, the THz probing also allows for an analysis of strongly
non-uniform thin films. Using scanning near-field terahertz and electron
microscopies, we relate the observed anisotropic conductivity of CuMnAs to the
elongation and orientation of growth defects, which influence the local
microscopic conductivity. We also demonstrate control over the morphology of
defects by using vicinal substrates.Comment: 33 pages, 16 figure
Molecular beam epitaxy of CuMnAs
We present a detailed study of the growth of the tetragonal polymorph of
antiferromagnetic CuMnAs by the molecular beam epitaxy technique. We explore
the parameter space of growth conditions and their effect on the
microstructural and transport properties of the material. We identify its
typical structural defects and compare the properties of epitaxial CuMnAs
layers grown on GaP, GaAs and Si substrates. Finally, we investigate the
correlation between the crystalline quality of CuMnAs and its performance in
terms of electrically induced resistance switching.Comment: 10 pages, 8 figures and supplementary materia
Atomically sharp domain walls in an antiferromagnet
The interest in understanding scaling limits of magnetic textures such as
domain walls spans the entire field of magnetism from its relativistic quantum
fundamentals to applications in information technologies. The traditional focus
of the field on ferromagnets has recently started to shift towards
antiferromagnets which offer a rich materials landscape and utility in
ultra-fast and neuromorphic devices insensitive to magnetic field
perturbations. Here we report the observation that domain walls in an epitaxial
crystal of antiferromagnetic CuMnAs can be atomically sharp. We reveal this
ultimate domain wall scaling limit using differential phase contrast imaging
within aberrationcorrected scanning transmission electron microscopy, which we
complement by X-ray magnetic dichroism microscopy and ab initio calculations.
We highlight that the atomically sharp domain walls are outside the remits of
established spin-Hamiltonian theories and can offer device functionalities
unparalleled in ferromagnets.Comment: 8 pages, 4 figures, Supplementary informatio
Symmetry and topology in antiferromagnetic spintronics
Antiferromagnetic spintronics focuses on investigating and using
antiferromagnets as active elements in spintronics structures. Last decade
advances in relativistic spintronics led to the discovery of the staggered,
current-induced field in antiferromagnets. The corresponding N\'{e}el
spin-orbit torque allowed for efficient electrical switching of
antiferromagnetic moments and, in combination with electrical readout, for the
demonstration of experimental antiferromagnetic memory devices. In parallel,
the anomalous Hall effect was predicted and subsequently observed in
antiferromagnets. A new field of spintronics based on antiferromagnets has
emerged. We will focus here on the introduction into the most significant
discoveries which shaped the field together with a more recent spin-off
focusing on combining antiferromagnetic spintronics with topological effects,
such as antiferromagnetic topological semimetals and insulators, and the
interplay of antiferromagnetism, topology, and superconductivity in
heterostructures.Comment: Book chapte
Preparation of samples for calibration of electron microscope magnification / 2016
We have been working on lithographical preparation of specimens used for magnification calibration of electron microscopes.\
Příprava a studium vlastností epitaxních feromagnetických vrstev GaMnAs
Matematicko-fyzikální fakultaFaculty of Mathematics and Physic
Systematic Study of Anisotropic Magnetoresistance in (Ga,Mn)As
AbstractWe systematically study the anisotropic magnetoresistance (AMR) on a series of optimized (Ga,Mn)As samples. The crystalline and non-crystalline contributions to the AMR were separated and an apparent higher-order term (of six-fold symmetry) was identified to be an artefact resulting from the presence of magnetic anisotropy of the material and of the residual fields of external superconducting magnets. In the broad range of nominal Mn concentrations from 2% to 11%, we find the non-crystalline contribution to dominate, although the crystalline terms become relatively more important for higher doping levels. We compare the AMR magnitude with the Boltzmann transport calculations based on the k·p mean-field kinetic-exchange model