Study On Current Regulation Of Magnetic Properties Of Nanomaterials Based On STT Effect

With the rapid development of electronic technology and military technology,the development of electromagnetic wave absorbing materials and components has gained more and more attention.In order to overcome electromagnetic interference(EMI)between electronic devices,magnetic electromagnetic wave absorbing materials are used to absorb harmful electromagnetic waves.For this purpose,it is necessary to absorb the unwanted electromagnetic radiation energy through the magnetic resonance(including natural resonance,magnetic domain wall resonance)or the eddy current effect of the material itself,which requires that the magnetic conductivity of the magnetic material is positive(?''>0).Electromagnetic wave metamaterial is one of the hot research fields,It can effectively control the transmission and reflection of electromagnetic waves,and can be used to develop invisibility cloaks,electromagnetic wave absorption components,high resolution imaging lenses and so on.At present,the electromagnetic artificial metamaterials reported in the working frequency range requires that its electromagnetic parameters meet certain conditions: both the dielectric constant and the permeability are less than 0.In particular,it is difficult to realize that the imaginary part of the permeability is less than 0(?' <0),regardless of natural materials or artificial structures.The main methods for regulating high frequency magnetic conductivity of magnetic materials are: heat treatment(microstructure of regulating materials),magnetic field orientation,magnetic shape control,etc.For artificial materials,the method of regulating high frequency permeability can only be used to design elements of different geometric shapes,and to adjust the size and spacing of units.Based on the spin transfer moment(STT)effect,when the spin polarized electrons in the polarization current interact with the local magnetic moment,the angular momentum of the spin polarized electron is transferred to the local magnetic moment.When the polarization current is applied in ferromagnetic materials,it will affect the dynamic behavior of the magnetic moment,and the precession behavior of the magnetic moment around the effective field is changed.In this way,the dynamic magnetic response of the material can be changed and the dynamic magnetic energy is different.In this paper,we use the micromagnetics simulation software OOMMF to study the change of dynamic magnetic energy of single and nanowire arrays under the action of polarization current.The current regulation of the magnetic permeability spectrum is realized and it is mainly realized that the imaginary value of the permeability is negative(?''<0).We find that the negative value is due to the interaction of the magnetic moment between the spin-polarized conduction electrons and the uneven distribution of magnetic moments at both ends of the nanowires.The results are well explained from the effect of spin transfer torque on the precession of magnetization under the excitation of both the pulsed magnetic field and polarization current.The full text is divided into two parts.The first part is the regulation of the magnetic permeability spectrum of the single nanowire with polarization current and the second part is extended to simulate the regulation of the polarization current on the magnetic permeability spectra of the nanowire array.We have found the effect of the length and diameter of the nanowires,the magnitude and direction of the polarization current and the damping constant and other parameters on the magnetic dynamic responses of the nanowires.