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Abstract Artificial spin ice (ASI) systems have emerged as powerful platforms for exploring the fundamental aspects of magnetic frustration and topological phenomena in condensed matter physics. In this study, we investigate the bountiful effects that result from introducing hexagonal magnetic defects into an ASI lattice. The stochastic stabilisation of a plethora of metastable states in the hexagonal defects are explored, as well as harnessing the defect magnetisation state for the selective injection of emergent monopoles of different polarities and proximities within the lattice. We demonstrate a mechanism for tailoring the ASI behaviour using the magnetic state of the defect, which is of interest to applications including magnetic memory devices and spin-based logic.

Artificial spin ice systems offer a promising platform to study the motion of emergent magnetic monopoles, but controlled nucleation of monopoles is challenging. Here the authors demonstrate controlled injection and propagation of emergent monopoles in an artificial spin ice utilizing ferromagnetic defects.

The rare-earth-free MnAlC alloy is currently considered a very promising candidate for permanent magnet applications due to its high anisotropy field and relatively high saturation magnetization and Curie temperature, besides being a low-cost material. In this work, we presented a simple fabrication route that allows for obtaining a magnetically enhanced bulk τ-MnAlC magnet. In the fabrication process, an electric arc-melting method was carried out to melt ingots of MnAlC alloys. A two-step solution treatment at 1200 °C and 1100 °C allowed us to synthesize a pure room-temperature ε-MnAlC ingot that completely transformed into τ-MnAlC alloy, free of secondary phases, after an annealing treatment at 550 °C for 30 min. The Rietveld refinements and magnetization measurements demonstrated that the quenched process produces a phase-segregated ε-MnAlC alloy that is formed by two types of ε-phases due to local fluctuation of the Mn. Room-temperature hysteresis loops showed that our improved τ-MnAlC alloy exhibited a remanent magnetization of 42 Am2/kg, a coercive field of 0.2 T and a maximum energy product, (BH)max, of 6.07 kJ/m3, which is higher than those reported in previous works using a similar preparation route. Experimental evidence demonstrated that the synthesis of a pure room-temperature ε-MnAlC played an important role in the suppression of undesirable phases that deteriorate the permanent magnet properties of the τ-MnAlC. Finally, magnetic images recorded by Lorentz microscopy allowed us to observe the microstructure and magnetic domain walls of the optimized τ-MnAlC. The presence of magnetic contrasts in all the observed grains allowed us to confirm the high-quality ferromagnetic behavior of the system.

Fe and Co nano-whiskers and Co platelets were synthesized via physical vapor deposition without any template and catalyst. Transmission electron microscopic analyses revealed that the Fe whiskers were all single crystal with whisker axis along [1 0 0] crystallographic direction. Both FCC and HCP crystal structures were found in the Co whiskers with stacking faults and micro-twins. Off-axis Electron holography results showed that all the whiskers synthesized were magnetic single domain structures. Vortex state was observed in a small platelet of high symmetry.

The different spin configurationsin the vicinity of the single-domain/vortextransition are reported in isolated magnetic nanoparticles. By combiningchemical synthesis, electron holography in a dedicated transmissionelectron microscope and micromagnetic simulations, we establish the“magnetic configurations vs size” phase diagram of Fesingle-crystalline nanocubes. Room temperature high resolution magneticmaps reveal the transition between single-domain and vortex statesfor Fe nanocubes from 25 to 27 nm, respectively. An intermediate spinconfiguration consisting of an ⟨111⟩ vortex is for thefirst time evidenced. [ABSTRACT FROM AUTHOR]

This article reports the synthesis of iron(0) nanoparticles at moderate temperature—from 120 °C to 150 °C—using the reduction of the organometallic iron(ii) precursor {Fe[N(SiMe3)2]2}2by hexadecylamine (HDA) in the absence of dihydrogen (H2). The nanoparticles are monodisperse in size and self-assemble into 2D super-lattices suitable for transport measurements. The nanoparticles are stabilized in mesitylene by a mixture of HDA and hexadecylammonium chloride (HDA·HCl). The resulting truncated single-crystalline nanocubes have a narrow size distribution and a high magnetization close to the bulk value. The products are characterized by transmission electronic microscopy (TEM and HRTEM), SQUID measurements, Mössbauer and Infra-Red spectroscopies. Fe(ii) reduction is accompanied by oxidation of amines into imines which was detected as a by-product. This reduction occurs at 120 °C and above. The temperature, in conjunction with the reaction time, allows for a fine control of the nano-objects final size. The latter can also be tuned with the HDA·HCl concentration. Finally, this one-pot synthesis produces high-quality magnetic nanoparticles with mean sizes in the range 6 to 10 nm depending on the conditions. [ABSTRACT FROM AUTHOR]