The micromagnetic simulation has been carried out to analyse and analyse the magnetic features of Permalloy nanostructures. The Object Oriented MicroMagnetic Framework ( OOMMF ) package has been used to gauge the values to analyze magnetic features.
The critical size of nanoisland of square form is estimated for passage from vortex province ( four spheres ) to a individual sphere province. The dependance of the magnetizing curve parametric quantity - coercive force for different thicknesses, countries and anisotropic invariables of nanoisland has been studied. The consequences estimated can be utile in making the topology of the elements of spintronics which is based on magnetic nanostructures.
Introduction
The storage denseness ofhard disc drivesis increasing along an exponential growing curve, since because spintronics based devices like GMR and TMR detectors have increased the sensitiveness of the read caput which even measures the magnetic province of really little magnetic spheres on the spinning platter.Single and multiple movie nanostructures have great belief for the development of memory matrixes and magnetic sensors with regard to magnetoresistance. So in order to develop a topology for magnetoresistive constructions, gauging their magnetic belongingss is of much of import. So it is indispensable to utilize a theoretical analysis of magnetic belongingss of nano constructions utilizing micromagnetic simulation. In this paper a simulation work has been made to analyze the magnetic features of individual bed, square shaped Permalloy nanostructures.Presents, the micromagnetic method of simulation has become a popular tool for theoretical analysis of nanosized magnetic systems.
Several micromagnetic simulation methods were published and in this work, a oommf simulation method has been used.The magnetic features of magnetic stuffs chiefly depend on their sizes and forms and this is due to fact that a magnetic system is pointed in cut downing isolated field flows by bring forthing peripheral spheres and magnetic whirls. Micromagnetic simulation gives us a opportunity for designation of qualitative and quantitative information of a alteration in the magnetic parametric quantities based on the geometry values of the sample.
Model of survey
As the first phase of survey, the demand of sphere construction on sidelong sizes of the nanoisland was determined when there is no external field.This corresponds wholly under the demagnetized province of the sample. It has been forecasted that magnetic features of ultra-thin magnetic movies relied on the theoretical account of individual sphere nanostructure atom.As the 2nd and 3rd phase of the work, it has been determined the function of the magnetizing curve parametric quantities like coercive force and anisotropy invariable on the nanoisland thickness and sidelong side.
Appraisal of a Critical Size for a Passage
to a Single-Domain State
The critical size of a square shaped nanoisland for passage from vortex province ( four spheres ) to a individual sphere province has been estimated here. For demagnetized sample, the distribution of magnetisation meets the lower limit of functional at the zero external Fieldss.A single-layer, square-shaped, movie Permalloy island is used as sample here.
Procedure of simulation
The anisotropy invariable ( K ) was taken to be zero. The thickness of the movie was taken as 10 nanometer. The length of the square varied from 100 nanometers to 30 nanometers. The computations of the sphere construction of a system at assorted sizes were carried out.The size of the cell besides varied from 10 to 1 nanometers so as to acquire the computation truth. Exchange interaction invariable ( A ) was taken as 1.3 - 10^-11 J/m^3, anisotropy ( K ) as 0J/m3, impregnation magnetisation ( Ms ) as 800kA/m and muffling coeffient as 0.5.
A mmDisp map in oommf is used to expose the magnetisation distribution.
Analysis of critical Size for a Passage to a Single-Domain State
As a consequence of modeling, the fake images of magnetisation distributions for the square shaped Permalloy with changing sizes were obtained. The cell size used here was 1 nm. As clearly shown from the above figures, it has been seen that with a lessening in the system size, the sphere construction alters.In the samples where the length of square is more than 80 nm, there are four spheres i.e. whirl province, whereas, in the sizes below 50nm there is a passage to the single-domain province. So for the samples where the side length is less than 50 nanometers, it is certain to conform that, the province transportations to the single-domain province.
This single-domain province is called the `` leaf province '' . Besides it has been observed that the individual sphere province is characterized by a really low energy barrier to jumping magnetisation bespeaking that thermic fluctuations are exchanging the system from one province into another province at even low temperatures. Therefore the consequences obtained allow us to analyse the magnetic features of ultra-thin magnetic movies based on single-domain nanosized atom theoretical account.
Dependence of the Coercive Force on the sample thickness
As the 2nd phase of survey, the dependance of the magnetizing curve parametric quantity - coercive force for different nanoisland thicknesses was determined.A inactive job on micromagnetism is solved at a specified value of the external magnetic field.
Procedure of simulation
In job editor of oommf, the stuff parametric quantities were given as - exchange interaction invariable ( A ) was taken to be equal to 1.3 - 10^-11 J/m^3. The single-axis anisotropy ( K ) varied on the bounds from 0 to 20000 J/m3. The impregnation magnetisation ( Ms ) was taken to be 800kA/m and muffling coeffient as 0.5.Then the changeless magnitude was chosen in demagnetisation bill of fare. In portion geometry the sample 's geometric specifications were included. The thickness of the island is changed from 10-100 nanometer. The cell size used in this job was 10 nanometer. The sidelong size of the island is fixed with the specified square as 250 x 250 nanometer ( width x tallness ) . A mask option was selected to import the square shaped sample.
The initial magnetisation is to be vortex. The field ranges has to be chosen right depending on the expected curve parametric quantities. If the end product curve is non clear to mensurate the parametric quantities, the field ranges has to be varied consequently until we get the clear end product curve. The external magnetic field was applied in plane of the movie, along the easy axis and it was varied from -200 to 200 Oe. Then this job editor values were loaded in Solve2D option.
Now mmGraph option is to be used to acquire the magnetisation curve. In Solve2D, mmGraph is selected in scheduled end products. Now the its clip to run the plan. For each value of the thickness, the corresponding magnetisation curve ( hysteresis cringle ) was obtained with same process and the value of the coercive force ( Hc ) is therefore calculated for different sample thicknesses. The dependance of the coercive force for different thicknesses of the nanoisland was simulated and included in the tabular array 1.
This shows dependances obtained for three different values of the anisotropy invariable ( i.e. for K = 0,1000,20000 J/m^3 ) .The anisotropy parametric quantity can be changed within broad bounds based on the fabrication technique of the sample under trial.
Fig. 2 shows graphical representation of the tabulated values. By analysing this graph, we can see that the given dependances have both general and strongly different features. An of import factor to observe down is, while increasing anisotropy changeless K, the coercive force additions instead in the little thickness parts. So we can indicate out that the value of the coercive force is to be determined by the magnetic anisotropy and the form anisotropy. The part of the anisotropy at little thicknesses seems to be ruling.
Then in big thickness parts, there is a common inclination to diminish the coercive force irrespective of anisotropy value while turning the thicknesses.The process to acquire the magnetisation curve for different sidelong sizes is same as explained before. Demur that as before the sidelong side is fixed and thickness was varies, but here thickness is fixed and sidelong side was varied. The dependance of the coercive force for different sidelong sides of the nanoisland is simulated and included in the tabular array 2.The dependance of the coercive force ( or coercivity ) depending on the size of sidelong side ( SX ) is represented diagrammatically in Fig. 3.
By analysing this graph, it is obvious to judge that the given dependances have a general characteristic, that is, a inclination on the coercive force decrease while increasing the sidelong sizes of the nanoisland. It is seen that the coercive force is diminishing depending on the factor of the form anisotropy on increasing the island size. So the anisotropy value plays an of import function in make up one's minding the sidelong size of the island for specific applications.A snapshot of typical hysteresis cringle curve obtained from oommf simulation is shown in Fig.
4. Sometimes an unusual form of the hysteresis cringle will be obtained and this is due to increasing the whirl province in the comparatively little Fieldss.
