Saturation (magnetic) | EPFL Graph Search

Seen in some magnetic materials, saturation is the state reached when an increase in applied external magnetic field H cannot increase the magnetization of the material further, so the total magnetic flux density B more or less levels off. (Though, magnetization continues to increase very slowly with the field due to paramagnetism.) Saturation is a characteristic of ferromagnetic and ferrimagnetic materials, such as iron, nickel, cobalt and their alloys. Different ferromagnetic materials have different saturation levels. Description Saturation is most clearly seen in the magnetization curve (also called BH curve or hysteresis curve) of a substance, as a bending to the right of the curve (see graph at right). As the H field increases, the B field approaches a maximum value asymptotically, the saturation level for the substance. Technically, above saturation, the B field continues increasing, but at the paramagnetic rate, which is several orders of magnitude smaller than

Synthesis, structural and magnetic characterization of thin films of the chiral magnets CoZnMn and FeGe

Skyrmions are topologically protected nanometer-sized magnetic vortices that have sparked interest for future spintronics applications aiming at high-density, high-speed and low-power consuming magnetic memory devices. One type of skyrmions appears in non-centrosymmetric materials with spin-orbit coupling. Bulk materials such as FeGe and CoZnMn have been in the focus of recent research as they host skyrmion lattices near or above room temperature. The interest in thin-film materials has immensely increased as they promise better control of skyrmions. The main challenges are the synthesis of skyrmion-hosting materials with high critical temperatures and the compatibility with Si-based thin-film technologies. Currently most of the studied thin films do not exhibit the relevant properties. It has been argued that strain and defects related to the lattice mismatch inhibit the skyrmion phase.Here we present novel approaches to synthesize skyrmion-hosting thin films based on FeGe and CoZnMn: 1) the crystallization of an amorphous thin film on a vdW substrate (commercial graphene), 2) van der Waals (vdW) growth on graphene as a substrate to achieve a strain- and defect-free growth of the overlayer.Sputtered FeGe layers were obtained on graphene on oxidized silicon substrates and annealed via rapid thermal (RTA) and flash lamp annealing (FLA). The goal was to use these annealing techniques to guide the material to the temperature/composition window of the cubic phase. For this, we varied the thin film thickness, Fe:Ge ratio, pre-heating and annealing temperature. The thin film temperature during the FLA was studied through heat transfer simulations. The experiments uncovered the long annealing time via RTA with a capping layer leads to 4 types of morphology: islands, discs, individual crystals and crystals on discs. The sub-second annealing via FLA led to the polycrystalline thin film formation. The obtained materials contain hexagonal and cubic FeGe, Fe-rich phases, pure Ge and Fe oxides analysed by Raman spectroscopy and X-ray diffraction. We provide Raman vibrational modes and the symmetry description from first-principles calculations for FeGex with x=1, 1.5 and 2 to fast and locally characterize thin films and microstructures.Molecular beam epitaxy was used to grow CoZnMn thin films of different stoichiometries on graphene on oxidized Si. It has been found in bulk crystals that the critical temperature can be systematically engineered beyond room temperature by tuning the composition. We report on the structural, compositional and magnetic properties of Co10-xZn10-yZnx+y (0

EPFL2021

Spin configurations in Co2FeAl0.4Si0.6 Heusler alloy thin film elements

André Bisig

We determine experimentally the spin structure of half-metallic Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following magnetic saturation, the dominant magnetic states consist of quasi-uniform configurations, where a strong influence from the magnetocrystalline anisotropy is visible. Heating experiments show the stability of the spin configuration of domain walls in confined geometries up to 800 K. The switching temperature for the transition from transverse to vortex walls in ring elements is found to increase with ring width, an effect attributed to structural changes and consequent changes in magnetic anisotropy, which start to occur in the narrower elements at lower temperatures. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3657828]

2011

Synthesis, structural and magnetic characterization of thin films of the chiral magnets CoZnMn and FeGe

EPFL2021