The spin wave modes of elongated magnetic islands arranged in Kagome artificial spin-ice arrays are micromagnetically simulated in the frequency regime between 3 and 16GHz. The edge modes are more ...suitable in order to detect the signatures of various types of local order of the spin-ice lattice as they are much more sensitive to the magnetic configurations of neighboring elements. The spectra of arrays consisting up to 30 elements can be decomposed to those originating from local magnetic states of their vertices.
Artificial Kagome spin ice arrays consisting of nanomagnets are model systems for the study of geometrical frustration, for which field demagnetization methods are insufficient to drive them in their ...ground states. Here the efficiency of different demagnetization protocols (involving rotation) is studied by micromagnetic simulations. The hysteresis loop of each element is greatly influenced by the magnetic state of the nearest neighbors, not only by the expected shift due to dipolar interaction bias, but as it regards the loop shape and width itself, which presents a correction to the usual macrospin calculation assumptions. It is shown that rotation in angular steps a little less than 180° is the most effective process in accessing the largest possible number states before ending up near the ground state even in the absence of any disorder which is shown to represent the most unfavorable case.
•Optimized athermal demagnetization process for a two-dimensional artificial kagome spin ice.•States with flux closure in small groups of elements difficult to obtain athermally in systems with N·30.•The dipolar interaction field not only biases but also changes the loop width.•Interactions lead to array size dependent remanence enhancement.
The magnetostatic bias in elongated nanomagnetic elements arranged in artificial Kagome spin ice arrays is studied by micromagnetic simulations. Using the Nmag package the reversal of a given element ...has been simulated under the influence of its four nearest neighbors with their magnetic states fixed in all possible configurations, which amount to 24=16 states that can be classified under five distinct cases. The hysteresis loop of each element is greatly influenced by the magnetic state of the nearest neighbors, not only by the expected shift due to dipolar interaction bias, but as it regards the loop shape and width itself. This presents a correction to the usual macrospin calculation based on the assumption that the loop is shifted by a biasing field (equal to the local dipole field) but the loop width (and shape in general) does not change. Although coercive and biasing fields depend strongly on the dimensions their relative strength has only weak thickness dependence for a fixed length to width aspect ratio. Therefore the behavior of such arrays is expected to be to a large degree size invariant apart from an appropriate maximum external applied field scaling.
The features that commonly appear in the First Order Reversal Curves (FORC) of magnetic composites, consisting of a hard and a soft phase, are reproduced by a simple mean-field approach in the limit ...of weak coupling. In this case the features corresponding to each phase are distinct and the effect of the interactions appears as biasing field on the soft phase and a coercivity reduction of the hard one. Interactions produce additional twin (positive/negative) interference features in the region of the (H, HR) FORC diagram where there is a strong dependence on H through the soft phase and on HR through the hard phase. The slope and the intensity of these twin features depend on interaction strength.
► FORCs of hard/soft magnetic composites are modeled in the limit of weak coupling. ► Interactions produce twin (positive/negative) interaction features. ► Slope and intensity of these twin features depend on interaction strength.
► We studied dilute-acid pretreatment of barley straw at low combined severity (−1.6 to 1.1). ► We monitored the production of fermentable sugars and the release of five inhibitory compounds. ► We ...optimized the pretreatment conditions at 170
°C, 0% sulfuric acid and 60
min. ► We used the ratio of Σsugars/Σinhibitors to evaluate the suitability of barley straw hydrolysates for fermentation purposes. ► We discussed the effect of the concentrations of the inhibitors on ethanol and hydrogen fermentability.
The production of fermentable substrates from barley straw under various process conditions was studied. Pretreatment included chemical pretreatment with dilute-acid followed by enzymatic hydrolysis; the pretreatment conditions were expressed in a combined severity factor, CS, which ranged in the present study from −1.6 to 1.1. Considering the production of fermentable sugars and the release of inhibitory compounds, the optimal pretreatment conditions were 170
°C, 0% sulfuric acid and 60
min, corresponding to CS −0.4. Under these conditions, 21.4
g glucose/L, 8.5
g xylose/L, and 0.5
g arabinose/L were produced, while 0.1
g HMF/L, 0.4
g furfural/L, 0.0
g levulinic acid/L, 0.0
g formic acid/L, and 2.1
g acetic acid/L were released. The ratio of Σsugars/Σinhibitors proved to be a good tool for evaluating the suitability of a hydrolysate for fermentation purposes.
•Vortices in NiFe nanocaps stabilized even for sizes for which they are not the lowest energy states.•Nanocaps by oblique deposition develop in-plane shape-anisotropy and increased ...coercivity.•Coercivity reduced up to by 36% using microwave assisted reversal.
Finite element micromagnetics are used to simulate remanence, hysteresis and dynamic switching in crescent shaped permalloy caps, a geometry that corresponds to either normal or oblique deposition of films on nanosphere arrays. Oblique deposition breaks the symmetry and favours onion states rather than vortices. It introduces in-plane shape anisotropy analogous to that of an elongated island and increases the in-plane coercivity. In isolated caps, the critical diameter above which the vortex state is the minimum energy state, is D = 123 nm for angles below θ = 20 deg. It increases with θ up to a vlaue of D = 157 nm at θ = 45 deg. Even for sizes for which the onion state is the lowest energy state, vortex states can be stabilized in isolated caps but the interparticle magnetostatic interactions tend to destabilize them driving the system to its ground state. The switching field of onion states can be reduced by 36% using microwave resonance at frequencies approaching the resonant (Kittel mode) frequencies.
► A 2-stage steam/organosolv pretreatment resulted in good sugar and lignin recovery. ► Close to 90% of the original xylan was recovered in a useable form. ► Close to 90% of the original cellulose ...could be hydrolysed at low enzyme loadings. ► The lignin recovered after 2-stage pretreatment was more reactive.
A two-stage pretreatment approach, employing steam followed by organosolv treatment, was assessed for its ability to fractionate and recover most of the hemicellulose, lignin and cellulose components of poplar wood chips. A mild steaming stage was initially used to maximise hemicellulose sugar recovery, with 63% of the original xylan solubilised and recovered after this stage and close to 90% recovered in total. Rather than hindering subsequent organosolv delignification, the prior steam treatment enhanced lignin solubilisation with more than 66% of the original lignin removed after the two-stage pretreatment. The extracted lignin contained at least equal or greater amounts of functional groups as compared to the lignin solubilised after a single-stage organosolv pretreatment. More than 98% of the original cellulose was recovered after the two-stage pretreatment and 88% of the cellulose could be hydrolysed to glucose at enzyme loading of 5FPU/g cellulose after 72h.
•Topological Hall effect found in Pt/Co/W multilayers with different signs of anisotropy.•Negative topological Hall contribution due to nucleated isolated skyrmions.•Positive topological Hall ...contribution isolated non-annihilated skyrmions.•Skyrmion numbers of complex domain structures reproduced micromagmetically.
The chirality of non-coplanar magnetic configurations, in magnetic materials with interfacial Dzyaloshinskii–Moriya interaction, gives rise to a local magnetic field generating an extra contribution to the anomalous Hall effect. This contribution, termed topological Hall effect (THE), is studied in three Pt/Co/W multi-layered samples with different effective anisotropy. A particularity of this system, compared to similar systems which show THE, is the existence of magnetically inactive layers at the Co/W interfaces. This implies that the coupling between the layers in this series of samples is mainly magnetostatic. The samples with positive or almost zero effective anisotropy show the same characteristics. These are reproduced by micromagnetic simulations. The sample with negative effective anisotropy shows a qualitatively different behaviour that can be assigned to its radically different domain structure. The values of THE are in the range 0.1–0.25 μΩ cm.
•Vortices on a family thin spherical sector shaped shells are stabilized by curvature.•Curvature is varied at constant size to single-out its contribution to vortex stabilization.•Stabilization is ...mainly driven by the exchange energy term.
Finite element micromagnetics are used to simulate the vortex and onion states on permalloy spherical shells with different curvatures. To distinguish between the effects of size and curvature (covaried in the typical semi-spherical or crescent shaped caps) a family of spherical sectors where the volume is varied at constant curvature is considered. This family is parametrized by intersecting cone angle. Permalloy is chosen as a typical case of an easy-surface magnet in which the demagnetization field bounds the magnetization to follow the curvature of the surface. The thickness of the shell is set to 3 nm, i.e. comparable to the exchange length, so that the local magnetization does not vary along the thickness of the shell. It is found that as the curvature increases the vortex states become favorable down to smaller sizes. This is mainly due to the increased exchange energy cost of the onion states at larger curvatures. Furthermore, it is found that at larger curvatures, stronger in-plane fields are required to destabilize the vortex states and turn them into onion states.
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