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We demonstrate large voltage-induced changes of magnetic properties in thin films of Ni80Fe20 (permalloy) when gated using an ionic liquid medium [1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI)]. The coercivity and magnetic moment of 5 nm thick permalloy films could be reduced by 75% and 35%, respectively, by using applied voltages. These changes were partially restored by reversing the potential polarity. Electrochemical, time-course magnetometry and surface analysis measurements suggest that the voltage-induced changes are due to changes in the oxidation state at the surface of the film, causing a thinning of the permalloy layer. The control of soft magnetic properties with low voltages may be of use in tuneable devices. [ABSTRACT FROM AUTHOR]

Ferromagnetic films with perpendicular magnetic anisotropy are of interest in spintronics and superconducting spintronics. Perpendicular magnetic anisotropy can be achieved in thin ferromagnetic multilayer structures, when the anisotropy is driven by carefully engineered interfaces. Devices with multiple interfaces are disadvantageous for our application in superconducting spintronics, where the current perpendicular to plane is affected by the interfaces. Robust intrinsic PMA can be achieved in certain Co x Pt 100 - x alloys and compounds at any thickness, without increasing the number of interfaces. Here, we grow equiatomic Co 50 Pt 50 and report a comprehensive study on the structural, magnetic, and spin-polarisation properties in the L 1 1 and L 1 0 ordered compounds. Primarily, interest in Co 50 Pt 50 has been in the L 1 0 crystal structure, where layers of Pt and Co are stacked alternately in the [100] direction. There has been less work on L 1 1 crystal structure, where the stacking is in the [111] direction. For the latter L 1 1 crystal structure, we find magnetic anisotropy perpendicular to the film plane. For the former L 1 0 crystal structure, the magnetic anisotropy is perpendicular to the [100] plane, which is neither in-plane or out-of-plane in our samples. We obtain a value for the ballistic spin polarisation of the L 1 1 and L 1 0 Co 50 Pt 50 to be 47 ± 3 % . [ABSTRACT FROM AUTHOR]

Insight into the nucleation, growth and phase transformations of calcium sulphate could improve the performance of construction materials, reduce scaling in industrial processes and aid understanding of its formation in the natural environment. Recent studies have suggested that the calcium sulphate pseudo polymorph, gypsum (CaSO4·2H2O) can form in aqueous solution via a bassanite (CaSO4·0.5H2O) intermediate. Some in situ experimental work has also suggested that the transformation of bassanite to gypsum can occur through an oriented assembly mechanism. In this work, we have exploited liquid cell transmission electron microscopy (LCTEM) to study the transformation of bassanite to gypsum in an undersaturated aqueous solution of calcium sulphate. This was benchmarked against cryogenic TEM (cryo‐TEM) studies to validate internally the data obtained from the two microscopy techniques. When coupled with Raman spectroscopy, the real‐time data generated by LCTEM, and structural data obtained from cryo‐TEM show that bassanite can transform to gypsum via more than one pathway, the predominant one being dissolution/reprecipitation. Comparisons between LCTEM and cryo‐TEM also show that the transformation is slower within the confined region of the liquid cell as compared to a bulk solution. This work highlights the important role of a correlated microscopy approach for the study of dynamic processes such as crystallisation from solution if we are to extract true mechanistic understanding. [ABSTRACT FROM AUTHOR]

The magnetic properties of exchange biased systems deposited on top of fullerene-based materials have been studied. An enhanced exchange bias field has been observed for Si/SiO2/C60/Co/Cu/Co/IrMn/Ta and Si/SiO2/FeC60/Co/Cu/Co/IrMn/Ta in comparison to a typical structure of Si/SiO2/Ta/Co/Cu/Co/IrMn/Ta. Here the magnetic properties of the devices are changed significantly with an organic underlayer or seed layer. The magnetic ordering is well maintained, and C60 seeding results in an exchange bias of (19.5 \pm 0.5) mT, some 7 mT higher than that of Ta seeded spin valves (12.5 \pm 0.5 mT). A combination of MOKE (magneto-optical Kerr effect), X-ray diffraction and Raman spectroscopy have been used to characterize the materials and further understand the interactions between the Co and fullerene-based materials. [ABSTRACT FROM AUTHOR]

We report on x-ray and neutron scattering studies that reveal the structure of interfaces of C60 layers with adjacent transition metal layers, in this instance, Cu. Such interfaces produce room-temperature long-range spin order that is not described by conventional theories of metallic magnetism. We use a combination of hard x-ray reflectivity and neutron scattering to investigate the interfacial structure of two C60/Cu layered samples: a superlattice with multiple C60/Cu repeats and a simpler tri-layer structure. For both structures, we develop a consistent structural model for the two scattering techniques, which details the critical interfacial roughness between the layers. We find that while x-ray reflectivity provides a strong contrast between the C60 and Cu layers, the similar neutron scattering length density of the two materials severely reduces the neutron scattering contrast. Our results can be used to design material systems that permit studies of the magnetism of the C60/transition metal interfaces with spin-sensitive scattering probes such as polarized neutron reflectometry. [ABSTRACT FROM AUTHOR]

The influence of iron replacement on the structural and magnetic properties of Dysprosium manganites was studied using the series of DyFe x Mn 1- x O 3 (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) compounds. All samples were fabricated by means of the modified auto-combustion sol-gel method, followed by the ball milling technique. Orthorhombic structure (Pnma space group) with high phase purity and crystallinity featured all samples, according to X-ray diffraction analysis. The temperature dependence of magnetization curves indicated antiferromagnetic (AFM) to paramagnetic (PM) transition with the increase in temperature. The Néel temperature (T N) was observed to shift to higher temperatures, whereas the spin reorientation transition temperature (T SR) reduced as Fe3+ content increased. Cusps in the zero-field-cooled (ZFC) curves were detected at low temperatures (around 4 K) as an indication of the ordering of the Dy spin. 57Fe Mӧssbauer spectra in samples with low iron content were dominated by a high spin (Fe3+) paramagnetic doublet at both 295 K and 78 K, while the distribution in the hyperfine magnetic field accounted for the appearance of the broadening magnetic peaks. High iron samples revealed a magnetic sextet with fit-resolved patterns that indicated a strong AFM coupling of Fe3+ ions. The hyperfine magnetic field (B hf) magnitude demonstrated a linear increase with the increase in iron doping. [ABSTRACT FROM AUTHOR]

We determine the collective spin excitations and their contribution to the intrinsic resistivity in 3 d ferromagnets by high field magnetotransport experiments. Well above the technical saturation of the magnetization, in the single domain magnetic state, the longitudinal magnetoresistance has a nonsaturating negative slope of about 0.02-0.05 µΩ cmT[sup -1] at 300 K for Fe, Co, and Ni. We demonstrate its magnetic origin and assign the effect to a decrease of the electron-magnon scattering due to the damping of spin waves in high field. A convincing agreement is found between the high field measurements and our theoretical calculation of the spin flip electron-magnon scattering. This provides a unique estimate of the pure magnetic resistivity in 3d ferromagnets. [ABSTRACT FROM AUTHOR]

Nanocrystalline Mn-doped magnetite ( Fe O) particles of the composition Mn Fe O $\left (x = 0.0, 0.1, 0.2, 0.3, 0.4 \text { and } 0.5; y = \frac {2x}{3}\right )$ , prepared using chemical precipitation under reflux with the Mn ions substituting for Fe ions rather than Fe ones, are characterized mainly with XRD and Fe Mössbauer spectroscopy. All samples were found to have spinel-related structures with average lattice parameters that increase linearly with the Mn concentration, x. The particle size for the samples varied from ∼8 nm to 23 nm. The oxidation of Fe to Fe at surface layers of the Fe O nanoparticles leading to the formation of maghemite ( γ- Fe O) was found to considerably weaken with increasing Mn concentration. The percentage of the nanoparticles that exhibit short range magnetic ordering due to cationic clustering and/or superparamagnetism increases from 17% to 32% with increasing x. The dependence of isomer shifts of the Fe nuclei at the tetrahedral and octahedral sites on dopant Mn concentration is emphasized. The electric quadrupole shifts indicate that the Mn Fe O particles undergo Verwey transition. The effective hyperfine magnetic fields at both crystallographic sites decrease with increasing Mn concentration reflecting a size effect as well as a weakening in the magnetic super-exchange interaction. The Mössbauer data indicate that for x ≤ 0.2, the dopant Mn ions substitute solely for octahedral Fe ions whereas for x > 0.2 they substitute for Fe at both tetrahedral and octahedral sites. [ABSTRACT FROM AUTHOR]

We use ferromagnetic resonance to study the current-induced torques in YIG/heavy metal bilayers. YIG samples with thickness varying from 14.8 nm to 80 nm, with the Pt or Ta thin film on top, are measured by applying a microwave current into the heavy metals and measuring the longitudinal DC voltage generated by both spin rectification and spin pumping. From a symmetry analysis of the FMR lineshape and its dependence on YIG thickness, we deduce that the Oersted field dominates over spin-transfer torque in driving magnetization dynamics. [ABSTRACT FROM AUTHOR]

In this work, we show that Fe3O4 films grown by oxygen plasma assisted molecular beam epitaxy have anomalous magnetic properties such as negative magnetoresistance and high saturation magnetic fields. The film substrate mismatch of 3% is relieved by the formation of misfit dislocations at the interface. Transmission electron microscopy results show that misfit dislocations are not the cause of antiphase domain boundary (APB). This suggests that in this system APB formation is a property of the three dimensional Fe3O4 growth. [ABSTRACT FROM AUTHOR]

We report spin wave propagation experiments in thin yttrium iron garnet (YIG) films. Using time-resolved scanning Kerr microscopy we extract the mode structure of the spin waves. For quasi-single-mode excitation, the spin wave decay can be fitted with a damped harmonic oscillator function providing us with information about the attenuation length. We measure values of about 2.7 and 3.6 μm for the spin wave decay length of 38- and 49-nm-thick YIG samples, respectively. Micromagnetic simulations are performed to compare experimental and simulated modes. The data are in very good agreement with these simulations. [ABSTRACT FROM AUTHOR]