21 research outputs found
Effect of the laser fluence on the microstructure and the relating magnetic properties of BaFe₁₂O₁₉ films grown on YSZ(111) by PLD for optimized perpendicular recording
High-quality BaFeO (BaM) films with high uniaxial anisotropy fields of H = 17.5 and 18.5 kOe were obtained by pulsed laser deposition (PLD) at two fluences of 1.5 and 5.1 J/cm on YSZ(111) substrate, using a platinum interlayer for reducing lattice mismatch. We demonstrated that the microstructure, morphology, and stoichiometry of the hexaferrite BaFeO films can be affected by raising the corresponding energy per pulse from 25 to 75 mJ. However, we also concluded that the increase of fluence leads to the formation of a non-stoichiometric BaM film through two nucleation steps and an output growth of small grains in addition to the increase of the defect density. In turn, this has contributed to the enhancement of the coercive field from H = 1769 Oe to H = 2166 Oe as it is required for the improvement of perpendicular recording resolution. We found that both the lateral coherent block size and misorientation of mosaic blocks are remarkably affected by the growth kinetics, which itself depends on the energy per pulse. For a deep understanding of the effect of laser fluence on the microstructure, chemical composition, and on the magnetic properties of thin BaM films, the results of complementary methods are combined. These methods comprise high-resolution X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy (TEM), scanning TEM combined with energy-dispersive X-ray spectroscopy, and vibrating sample magnetometer
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
Contributions from coherent and incoherent lattice excitations to ultrafast optical control of magnetic anisotropy of metallic films
Spin-lattice coupling is one of the most prominent interactions mediating response of spin ensemble to ultrafast optical excitation. Here we exploit optically generated coherent and incoherent phonons to drive coherent spin dynamics, i.e. precession, in thin films of magnetostrictive metal Galfenol. We demonstrate unambiguously that coherent phonons, also seen as dynamical strain generated due to picosecond lattice temperature raise, give raise to magnetic anisotropy changes of the optically excited magnetic film; and this contribution may be comparable to or even dominate over the contribution from the temperature increase itself, considered as incoherent phonons
Giant reversible nanoscale piezoresistance at room temperature in Sr2IrO4 thin films
Layered iridates have been the subject of intense scrutiny on account of
their unusually strong spin-orbit coupling, which opens up a narrow gap in a
material that would otherwise be a metal. This insulating state is very
sensitive to external perturbations. Here, we show that vertical compression at
the nanoscale, delivered using the tip of a standard scanning probe microscope,
is capable of inducing a five orders of magnitude change in the room
temperature resistivity of Sr2IrO4. The extreme sensitivity of the electronic
structure to anisotropic deformations opens up a new angle of interest on this
material, and the giant and fully reversible perpendicular piezoresistance
makes iridates a promising material for room temperature piezotronic devices
Entropy-controlled fully reversible nanostructure formation of Ge on miscut vicinal Si(001) surfaces
Crystal structure evolution in the van der Waals transition metal trihalides
Most transition-metal trihalides are dimorphic. The representative
chromium-based triad, CrCl3, CrBr3, CrI3, is characterized by the
low-temperature phase adopting the trigonal BiI3 type while the structure of
the high-temperature phase is monoclinic of AlCl3 type (C2/m). The structural
transition between the two crystallographic phases is of the first-order type
with large thermal hysteresis in CrCl3 and CrI3. We studied crystal structures
and structural phase transitions of vanadium-based counterparts VCl3, VBr3, and
VI3 by measuring specific heat, magnetization, and X-ray diffraction as
functions of temperature and observed an inverse situation. In these cases, the
high-temperature phase has a higher symmetry while the low-temperature
structure reveals a lower symmetry. The structural phase transition between
them shows no measurable hysteresis in contrast to CrX3. Possible relations of
the evolution of the ratio c/a of the unit cell parameters, types of crystal
structures, and nature of the structural transitions in V and Cr trihalides are
discussed.Comment: 11 pages, 6 figures, 1 table. J. Phys.: Condens. Matter (2022