Investigation of magnetic anisotropy and heat dissipation in thin films of compensated antiferromagnet CuMnAs by pump–probe experiment

We recently reported on a method to determine the easy axis position in a 10 nm thick film of the fully compensated antiferromagnet CuMnAs. The film had a uniaxial magnetic anisotropy and the technique utilized a magneto-optical pump and probe experiment [Saidl et al. Nat. Photonics 11, 91 (2017)]. In this contribution, we discuss the applicability of this method for the investigation of a broader set of epitaxial CuMnAs films having different thicknesses. This work reveals that the equilibrium magnetic anisotropy can be studied only in samples, where this anisotropy is rather strong. However, in the majority of CuMnAs films, the impact of a strong pump pulse induces nano-fragmentation of the magnetic domains and, therefore, the magnetic anisotropy measured by the pump–probe technique differs substantially from that in the equilibrium conditions. We also demonstrate that the optical pump–probe experiment can be used very efficiently to study the local heating and heat dissipation in CuMnAs epitaxial layers. In particular, we determined the electron–phonon relaxation time in CuMnAs. We also observed that, for a local film heating by a focused laser, the thinner films are heated more, but the heat is dissipated considerably faster than in the case of thicker films. This illustrates that the optical pump–probe experiment is a valuable characterization tool for the heat management optimization in the CuMnAs memory devices and can be applied in a similar way to those used during the heat-assisted magnetic recording technology development for the latest generation of hard drive disks

Multiple-stable anisotropic magnetoresistance memory in antiferromagnetic MnTe

Commercial magnetic memories rely on the bistability of ordered spins in ferromagnetic materials. Recently, experimental bistable memories have been realized using fully compensated antiferromagnetic metals. Here we demonstrate a multiple-stable memory device in epitaxial MnTe, an antiferromagnetic counterpart of common II–VI semiconductors. Favourable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the writing magnetic field angle, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states, which we set by heat-assisted magneto recording and by changing the writing field direction. The multiple stability in our memory is ascribed to different distributions of domains with the Neel vector aligned along one of the three magnetic easy axes. The robustness against strong magnetic field perturbations combined with the multiple stability of the magnetic memory states are unique properties of antiferromagnets

Investigation of magneto-structural phase transition in FeRh by reflectivity and transmittance measurements in visible and near-infrared spectral region

Magneto-structural phase transition in FeRh epitaxial layers was studied optically. It is shown that the transition between the low-temperature antiferromagnetic phase and the high-temperature ferromagnetic phase is accompanied by a rather large change of the optical response in the visible and near-infrared spectral ranges. This change is consistent with ab initio calculations of reflectivity and transmittance. Phase transition temperatures in a series of FeRh films with thicknesses ranging from 6 to 100 nm is measured thereby demonstrating the utility of the method to quickly characterise samples. Spatially resolved imaging of their magnetic properties with a micrometer resolution shows that the phase transition occurs at different temperatures in different parts of the sample

Control of antiferromagnetic spin axis orientation in bilayer Fe/CuMnAs films

Using x-ray magnetic circular and linear dichroism techniques, we demonstrate a collinear exchange coupling between an epitaxial antiferromagnet, tetragonal CuMnAs, and an Fe surface layer. A small uncompensated Mn magnetic moment is observed which is antiparallel to the Fe magnetization. The staggered magnetization of the 5 nm thick CuMnAs layer is rotatable under small magnetic fields, due to the interlayer exchange coupling. This allows us to obtain the x-ray magnetic linear dichroism spectra for different crystalline orientations of CuMnAs in the (001) plane. This is a key parameter for enabling the understanding of domain structures in CuMnAs imaged using x-ray magnetic linear dichroism microscopy techniques

Antiferromagnetic structure in tetragonal CuMnAs thin films

Tetragonal CuMnAs is an antiferromagnetic material with favourable properties for applications in spintronics. Using a combination of neutron diffraction and x-ray magnetic linear dichroism, we determine the spin axis and magnetic structure in tetragonal CuMnAs, and reveal the presence of an interfacial uniaxial magnetic anisotropy. From the temperature-dependence of the neutron diffraction intensities, the Néel temperature is shown to be (480 ± 5) K. Ab initio calculations indicate a weak anisotropy in the (ab) plane for bulk crystals, with a large anisotropy energy barrier between in-plane and perpendicular-to-plane directions

Spin transport and spin torque in antiferromagnetic devices

Ferromagnets are key materials for sensing and memory applications. In contrast, antiferromagnets which represent the more common form of magnetically ordered materials, have found less practical application beyond their use for establishing reference magnetic orientations via exchange bias. This might change in the future due to the recent progress in materials research and discoveries of antiferromagnetic spintronic phenomena suitable for device applications. Experimental demonstration of the electrical switching and detection of the Néel order open a route towards memory devices based on antiferromagnets. Apart from the radiation and magnetic-field hardness, memory cells fabricated from antiferromagnets can be inherently multilevel, which could be used for neuromorphic computing. Switching speeds attainable in antiferromagnets far exceed those of ferromagnetic and semiconductor memory technologies. Here we review the recent progress in electronic spin-transport and spin-torque phenomena in antiferromagnets that are dominantly of the relativistic quantum mechanical origin. We discuss their utility in pure antiferromagnetic or hybrid ferromagnetic/antiferromagnetic memory devices

Investigation of magneto-structural phase transition in FeRh by reflectivity and transmittance measurements in visible and near-infrared spectral region

Magneto-structural phase transition in FeRh epitaxial layers was studied optically. It is shown that the transition between the low-temperature antiferromagnetic phase and the high-temperature ferromagnetic phase is accompanied by a rather large change of the optical response in the visible and near-infrared spectral ranges. This change is consistent with ab initio calculations of reflectivity and transmittance. Phase transition temperatures in a series of FeRh films with thicknesses ranging from 6 to 100 nm is measured thereby demonstrating the utility of the method to quickly characterise samples. Spatially resolved imaging of their magnetic properties with a micrometer resolution shows that the phase transition occurs at different temperatures in different parts of the sample

Investigation of magneto-structural phase transition in FeRh by reflectivity and transmittance measurements in visible and near-infrared spectral region

Magneto-structural phase transition in FeRh epitaxial layers was studied optically. It is shown that the transition between the low-temperature antiferromagnetic phase and the high-temperature ferromagnetic phase is accompanied by a rather large change of the optical response in the visible and near-infrared spectral ranges. This change is consistent with ab initio calculations of reflectivity and transmittance. Phase transition temperatures in a series of FeRh films with thicknesses ranging from 6 to 100 nm is measured thereby demonstrating the utility of the method to quickly characterise samples. Spatially resolved imaging of their magnetic properties with a micrometer resolution shows that the phase transition occurs at different temperatures in different parts of the sample