Influence of Ga^+ ion irradiation on the magnetisation reversal process and magnetoresistance in CoFe/Cu/CoFe/IrMn spin valves

Ga^＋ ion irradiation is performed on the surfaces of IrMn-based spin valves and the effects of ion irradiation on the magnetisation reversal process and magnetoresistance （MR） are investigated. The results show that the exchange bias field and magnetoresistance ratio of the spin valve decrease with the increase of ion dose. The width of the forward step between the free layer and the pinned layer becomes gradually smaller with the increase of ion dose whilst the recoil step tends to be narrower with ion dose increasing up to 6×10^13 ions/cm^2 and the step disappears afterwards. Two oeaks in the R-H curve are found to be asymmetric.

Study of a collisionless magnetized plasma sheath with nonextensively distributed species

A weakly magnetized sheath for a collisionless, electronegative plasma comprising positive ions,electrons, and negative ions is investigated numerically using the fluid approach. The electrons are considered to be non-Maxwellian in nature and are described by Tsalli's distribution. Such electrons have a substantial effect on the sheath properties. The study also reveals that non-Maxwellian distribution is the most realistic description for negative ions in the presence of an oblique magnetic field. In addition to the negative ion temperature, the sheath potential is also affected by the nonextensive parameters. The present research finds application in the plasma processing and semiconductor industry as well as in space plasmas.

Dependence of Nanocrystalline Phase Formation and Magnetic Properties in Fe_(25)Ni_(75) on Ball Milling Time

Nanocrystalline Fe 25 Ni 75 powders were prepared by the mechanical alloying process . They were investigated by X ray diffraction and magnetic measurements .The ball milling time dependence of grain size, internal strain and magnetic properties has been discussed. The results show that the formation of Fe 25 Ni 75 alloy phase is almost completed after milling for 30 hours. The reduction of grain size accompanied by the growth of internal strain was observed after extended milling. An average grain size about 10-20 nm of alloyed powders has been determined by Sherrer formula estimation. The saturation magnetisation Ms has a slight increase when the average grain size continues to decrease by intensive milling. This fine size of mechanically alloyed powders (10-20 nm) results in a single domain magnetic structure and the formation of superparamagnetic phase.

Investigation of electric fields inside and outside a magnetised cold plasma sphere

Based on the scales transformation of electromagnetic theory, the analytical expressions of electric fields inside and outside a magnetised cold plasma sphere are presented by reforming the spherical electromagnetic parameter. The obtained results are in good agreement with that in the literature. The angle between the direction of inside field and that of outside field is derived. In S wave band, calculations for the effects induced by parameters of the inner field are established. Simulations show that the angle between incident field and the outside magnetic field influences the inner field remarkably. The inner field will increase as the electron density increases. The inner field varies with frequency nonlinearly. There is an angle between the inner field and the incident field, it changes nonlinearly with the frequency.

Numerical simulation of dynamic loss and total loss in the REBCO tapes under perpendicular AC magnetic fields up to 8 T at 20 K and 50 K

REBCO tapes carry DC current under AC magnetic fields in proposed HTS fusion applications. AC loss will be generated in the process and it is important to understand the AC loss behaviour for safe operation of the fusion magnets. In this work, magnetisation loss (Qm), dynamic resistance (Rdyn), and total loss (Qtotal) in four different REBCO tapes are numerically studied, using the measured and , for the magnetic field amplitude applied perpendicularly up to 8 T at 20 K and 50 K, where represents the magnetic field and field angle () dependent critical current density. The peak of Theva data is different from that of other tapes. We artificially shifted the ab-plane peak of Theva to the left by 25° to match the peak value. The newly shifted data is named as Theva-shift, which was also investigated to study the influence of the Theva peak shift on AC loss. The normalised DC transport current level (i = It/Ic0) ranges from 0.05 to 0.9, where the DC current amplitude and the self-critical current of the tape are represented by It and Ic0, respectively. The simulation results show that the AC losses deviate significantly from the Brandt-Indenbom (BI) equation at high magnetic fields. Jc and instantaneous loss curves for different tapes show correlation at high magnetic fields. The simulation results also show how different characteristics for different tapes influence AC losses. When AC loss values are scaled by the self-field critical current, Qm without current and Qtotal with current in the different tapes show a good agreement. It implies that the temperature dependence of the two types of loss can be calculated from a known loss at one temperature and the self-field critical current.

On the Growth Mechanism of Nickel and Cobalt Nanowires and Comparison of Their Magnetic Properties

Magnetic nanowires(NWs)are ideal materials for the fabrication of various multifunctional nanostructures which can be manipulated by an external magnetic fi eld.Highly crystalline and textured nanowires of nickel(Ni NWs)and cobalt(Co NWs)with high aspect ratio(~330)and high coercivity have been synthesized by electrodeposition using nickel sulphate hexahydrate(NiSO_(4)·6H_(2)O)and cobalt sulphate heptahydrate(CoSO_(4)·7H_(2)O)respectively on nanoporous alumina membranes.They exhibit a preferential growth along〈110〉.A general mobility assisted growth mechanism for the formation of Ni and Co NWs is proposed.The role of the hydration layer on the resulting one-dimensional geometry in the case of potentiostatic electrodeposition is verified.A very high interwire interaction resulting from magnetostatic dipolar interactions between the nanowires is observed.An unusual low-temperature magnetisation switching for fi eld parallel to the wire axis is evident from the peculiar high fi eld M(T)curve.

Advanced Monte Carlo Study of the Goldstone Mode Singularity in the 3D XY Model

Advanced Monte Carlo simulations of magnetisation and susceptibility in 3D XY model are performed at two different coupling constantsβ=0.55 andβ=0.5,completing our previous simulation results with additional data points and extending the range of the external field to twice as small values as previously reported(h≥0.00015625).The simulated maximal lattices sizes are also increased from L=384 to L=512.Our aim is an improved estimation of the exponentρ,describing the Goldstone mode singularity M(h)=M(+0)+chρat h→0,where M is the magnetisation.The data reveal some unexpected small oscillations.It makes the estimation by manyparameter fits of the magnetisation data unstable,and we are looking for an alternative method.Our best estimateρ=0.555(17)is extracted from the analysis of effective exponents determined from local fits of the susceptibility data.This method gives stable and consistent results for both values ofβ,taking into account the leading as well as the subleading correction to scaling.We report also the values of spontaneous magnetisation.