Magnetotransport measurements of NiFe thin films and nanostructures

A custom built thermal evaporator equipped with in situ electrical transport probes and an electromagnet, designed to investigate magnetic thin films and nanostructures, was constructed and calibrated. Magnetoresistance measurements were used to characterise a 20 nm thick film grown in 2 nm steps and measured in situ as a function of film thickness. It was found that the thin film had a smaller than expected anisotropic magnetoresistance (AMR) signal of 0.024%. It was suggested that an oxide formed at each 2nm thick layers during the growth phase altered the conductivity of the film and caused the measured AMR to be anomalously small. Lateral spin valves fabricated from a range of ferromagnetic and normal metal components were investigated. NiFe/Au/NiFe lateral spin valves were the most thoroughly investigated to determine the spin diffusion length in the Au, the spin polarisation of NiFe and the injection efficiency at the NiFe/Au interface. Lateral spin valves fabricated from NiFe/Al/NiFe and utilising tunnelling contacts were also investigated and a pure spin current detected. Other devices, including a non-local lateral spin valve dual spin injection structure, were fabricated and measured. Nanomachining using diamond coated silicon nitride atomic force microscope (AFM) tips was employed to modify nickel iron (NiFe) nanowires. The modifications to nanowires in this way subsequently altered the observed domain wall motion in the wires. AFM nanomachining was found mostly to increase the coercive field of the nanowires owing to the formation of a pinning site for domain walls. Magnetoresistance measurements were used to study the effect of machining nanowires of varying widths and thickness. Theoretical predictions regarding the change in coercive field due to machining were larger than those experimentally measured. Domain wall anisotropic magnetoresistance (DW AMR) was also studied as a function of width for two thicknesses of nanowire (10nm and 20nm). Deviation from existing theoretical models was observed consistently for both wire thicknesses. A dependence of the DW AMR on the proximity to the phase boundary between different domain wall types was observed for each thickness of nanowire studied

Investigation of nanoscale scratching on copper with conical tools using particle-based simulation

In this study, a modeling approach based on smooth particle hydrodynamics (SPH) was implemented to simulate the nanoscale scratching process using conical tools with different negative rake angles. The implemented model enables the study of the topography of groove profiles, scratching forces, and the residual plastic strain beneath the groove. An elastoplastic material model was employed for the workpiece, and the tool–workpiece interaction was defined by a contact model adopted from the Hertz theory. An in-house Lagrangian SPH code was implemented to perform nano-scratching simulations. The SPH simulation results were compared with nanoscale scratching experimental data available in the literature. The simulation results revealed that the normal force was more dominant compared to the cutting force, in agreement with experimental results reported for a conical tip tool with a 60° negative rake angle. In addition, the simulated groove profile was in good agreement with the groove profile produced in the aforementioned experiment. The numerical simulations also showed that the normal and cutting forces increased with the increase in the scratching depth and rake angle. Although the cutting and ploughing mechanisms were noticed in nano-scratching, the ploughing mechanism was more dominant for increased negative rake angles. It was also observed that residual plastic strain exists below the groove surface, and that the plastically deformed layer thickness beneath a scratched groove is larger for more negative values of the tool rake angle and higher scratching depths

Stress‐induced Domain Wall Motion in a Ferroelastic Mn3+ Spin Crossover Complex

Domain wall motion is detected for the first time during the transition to a ferroelastic and spin‐state ordered phase of a spin crossover complex. Single crystal X‐ray diffraction and resonant ultrasonic spectroscopy (RUS) revealed two distinct symmetry‐breaking phase transitions in the mononuclear Mn 3+ compound [Mn(3,5‐diBr‐sal 2 (323))]BPh 4 , 1. The first at 250 K, involves the space group change Cc → Pc and is thermodynamically continuous, while the second, Pc → P1 at 85 K, is discontinuous and related to spin crossover and spin‐state ordering. Stress‐induced domain wall mobility was detected as softening of the phonon modes at the Pc → P1 transition

Modulation of Mn³⁺ Spin State by Guest Molecule Inclusion

Spin state preferences for a cationic Mn3+ chelate complex in four different crystal lattices are investigated by crystallography and SQUID magnetometry. The [MnL1]+ complex cation was prepared by complexation of Mn3+ to the Schiff base chelate formed from condensation of 4-methoxysalicylaldehyde and 1,2-bis(3-aminopropylamino)ethane. The cation was crystallized separately with three polyatomic counterions and in one case was found to cocrystallize with a percentage of unreacted 4-methoxysalicylaldehyde starting material. The spin state preferences of the four resultant complexes [MnL1]CF3SO3·xH2O, (1), [MnL1]PF6·xH2O, (2), [MnL1]PF6·xsal·xH2O, (2b), and [MnL1]BPh4, (3), were dependent on their ability to form strong intermolecular interactions. Complexes (1) and (2), which formed hydrogen bonds between [MnL1]+, lattice water and in one case also with counterion, showed an incomplete thermal spin crossover over the temperature range 5–300 K. In contrast, complex (3) with the BPh4−, counterion and no lattice water, was locked into the high spin state over the same temperature range, as was complex (2b), where inclusion of the 4-methoxysalicylaldehyde guest blocked the H-bonding interaction

Crystallographic detection of the spin state in Fe^III complexes

[Image: see text] We report a single example of thermal spin crossover in a series of Fe(III) complexes, [Fe(III)(R-sal(2)323)](+), which typically stabilize the low-spin (S = 1/2) state. Single-crystal X-ray diffraction analysis of 53 such complexes with varying “R” groups, charge-balancing anions, and/or lattice solvation confirms bond lengths in line with an S = 1/2 ground state, with only the [Fe(III)(4-OMe-sal(2)323)]NO(3) complex (1a) exhibiting longer bond lengths associated with a percentage of the spin sextet form at room temperature. Structural distortion parameters are investigated for the series. A magnetic susceptibility measurement of 1a reveals a gradual, incomplete transition, with T(1/2) = 265 K in the solid state, while Evans method NMR reveals that the sample persists in the low-spin form in solution at room temperature. Computational analysis of the spin state preferences for the cations [Fe(III)(4-OMe-sal(2)323)](+) and [Fe(III)(sal(2)323)](+) confirmed the energetic preference for the spin doublet form in both, and the thermal spin crossover in complex 1a is therefore attributed to perturbation of the crystal packing on warming

Proton‐induced spin state switching in an Fe III complex

Reversible proton-induced spin state switching of an FeIII complex in solution is observed at room temperature. A reversible magnetic response was detected in the complex, [FeIII(sal2323)]ClO4 (1), using Evans’ method 1H NMR spectroscopy which indicated cumulative switching from low-spin to high-spin upon addition of one and two equivalents of acid. Infrared spectroscopy suggests a coordination-induced spin state switching (CISSS) effect, whereby protonation displaces the metal-phenoxo donors. The analogous complex, [FeIII(4-NEt2-sal2323)]ClO4 (2), with a diethylamino group on the ligand, was used to combine the magnetic change with a colorimetric response. Comparison of the protonation responses of 1 and 2 reveals that the magnetic switching is caused by perturbation of the immediate coordination sphere of the complex. These complexes constitute a new class of analyte sensor which operate by magneto-modulation, and in the case of 2, also yield a colorimetric response.</p