Strongly-interacting artificial spin systems are moving beyond mimicking naturally-occuring materials to find roles as versatile functional platforms, from reconfigurable magnonics to designer magnetic metamaterials. Typically artificial spin systems comprise nanomagnets with a single magnetisation texture: collinear macrospins or chiral vortices. By tuning nanoarray dimensions we achieve macrospin/vortex bistability and demonstrate a four-state metamaterial spin-system 'Artificial Spin-Vortex Ice' (ASVI). ASVI is capable of adopting Ising-like macrospins with strong ice-like vertex interactions, in addition to weakly-coupled vortices with low stray dipolar-field. The enhanced bi-texture microstate space gives rise to emergent physical memory phenomena, with ratchet-like vortex training and history-dependent nonlinear training dynamics. We observe vortex-domain formation alongside MFM tip vortex-writing. Tip-written vortices dramatically alter local reversal and memory dynamics. Vortices and macrospins exhibit starkly-differing spin-wave spectra with analogue-style mode-amplitude control via vortextraining and mode-frequency shifts of ∆ f = 3.8 GHz. We leverage spin-wave 'spectral fingerprinting' for rapid, scaleable readout of vortex and macrospin populations over complex training-protocols with applicability for functional magnonics and physical memory.
Strongly-interacting nanomagnetic arrays are finding increasing use as model host systems for reconfigurable magnonics. The strong inter-element coupling allows for stark spectral differences across a broad microstate space due to shifts in the dipolar field landscape. While these systems have yielded impressive initial results, developing rapid, scaleable means to access a broad range of spectrally-distinct microstates is an open research problem. We present a scheme whereby square artificial spin ice is modified by widening a ‘staircase’ subset of bars relative to the rest of the array, allowing preparation of any ordered vertex state via simple global-field protocols. Available microstates range from the system ground-state to high-energy ‘monopole’ states, with rich and distinct microstate-specific magnon spectra observed. Microstate-dependent mode-hybridisation and anticrossings are observed at both remanence and in-field with dynamic coupling strength tunable via microstate-selection. Experimental coupling strengths are found up to g/2π = 0.16 GHz. Microstate control allows fine mode-frequency shifting, gap creation and closing, and active mode number selection.
Strongly-interacting nanomagnetic arrays are crucial across an ever-growing suite of technologies. Spanning neuromorphic computing, control over superconducting vortices and reconfigurable magnonics, the utility and appeal of these arrays lies in their vast range of distinct, stable magnetization states. Different states exhibit different functional behaviours, making precise, reconfigurable state control an essential cornerstone of such systems. However, few existing methodologies may reverse an arbitrary array element, and even fewer may do so under electrical control, vital for device integration. We demonstrate selective, reconfigurable magnetic reversal of ferromagnetic nanoislands via current-driven motion of a transverse domain wall in an adjacent nanowire. The reversal technique operates under all-electrical control with no reliance on external magnetic fields, rendering it highly suitable for device integration across a host of magnonic, spintronic and neuromorphic logic architectures. Here, the reversal technique is leveraged to realize two fully solid-state reconfigurable magnonic crystals, offering magnonic gating, filtering, transistor-like switching and peak-shifting without reliance on global magnetic fields.
A series of high quality BaFe 2−x Ni x As 2 pnictide superconductors were studied using magnetic relaxation and isothermal magnetic measurements in order to study the second magnetization peak (SMP) and critical current behaviour in Ni-doped 122 family. The temperature dependence of the magnetic relaxation rate suggests a pinning crossover, whereas, it's magnetic field dependence hints a vortex-lattice structural phase-transition. The activation energy (U ) estimated using the magnetic relaxation data was analyzed in detail for slightly-underdoped, slightly-overdoped and an overdoped samples, using Maley's method and collective creep theory. Our results confirm that the SMP in these samples is due to the collective (elastic) to plastic creep crossover as has been observed for the other members of 122-family. In addition, we also investigated the doping dependence of the critical current density (J c ) and the vortex-pinning behaviour in these compounds. The observed J c is higher than the threshold limit (10 5 A/cm 2 ) considered for the technological potential and even greater than 1 MA/cm 2 for slightly underdoped Ni-content, x = 0.092 sample. The pinning characteristics were analyzed in terms of the models developed by Dew-Hughes and Griessen et al, which suggest the dominant role of δl-type pinning.
Some work leading to syntheses of oestrone is presented. It was generally found necessary to protect the 1 -carbony1 function in 5,6,7,7a-tetrahydro-8p-methylindane-l,5-dione before the introduction of alkyl groups a t position 4. Alkylations of 2-methylcyclopentane-1.3-dione have been made and the results compared with similar studies on 2meth ylcyclo hexane-1.3 -d ione.Devon THE total synthesis of oestrone has been achieved by relatively short and straightforward routes.l-1° We present here some of the background to our own work in this field, the aim of which was the synthesis of the hormone from 2-methylcyclopent ane-l,3-dionea l1Attempted alkylation of 5,6,7,7a-tetrahydro-7apmethylindane-1,5-dione,l2 (1 ; R = H) at position 4 yielded disappointing results, probably owing to the inst ability of the compound under basic ~0nditions.l~ Attempted protection of the l-carbonyl function by ethylene acetal formation proceeded poorly ; the chief products were unchanged dione and the diacetal. Reduction of the dione (10; R = H) with sodium borohydride gave 5,6,7,7a-tetrahydro-lp-hydroxy-7apmethylindan-&one * (2; R1 = R2 = H), the benzoyl derivative of which has been described previously as an 0i1.l~ This derivative was subsequently obtained as a crystalline solid, m.p. 85", A,, (ethanol) 235 nm. (E 26,000) and from the same experiment the enol bnzoate (3; R1 = Bz, R2 = BzO), lux. (ethanol) 242 nm. (E 33,400) was also secured. The formation of the latter was the first evidence that the desired 3,5-diene system, necessary for alkylation at the 4-position, could be readily formed under basic conditions.The tetrahydropyranyl ether (2; R1 = C,H,O, R2 = H) was then studied. Its solution in ether could be titrated with sodium triphenylmethanide ; l 5 the red colour of the reagent appeared a t the exact equivalence point. Methylation of this ether l6 gave, after hydrolysis, the compound (2; R1 = H, R2 = Me) (55%), which * Only the one enantiomer is named and depicted. All compounds are racemic.
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