Remanence Characteristic of Nanostructure of Hard／Soft Magnetic Multilayered Systems

The relation between microscopic properties (e.e.,layer thickness,easy axis orientation) and the macroscopic magnetic properties such as remanent magnetization of the ferromagnetic multilayer system is investigated based on a simple micromagnet approach.We concentrate on a multilayer design with periodic boundary condition,where alternating soft/hard layers build a nanostructured multilayer.For any easy axis direction in the soft and hard layers a simple explicit expression of remanence of the system has been derived analytically.We find that the remanence clearly depends on the thickness of the soft magnetic layer and is nearly independent of the thickness of hard magnetic layer.On the other hand,the remanence increases upon reducing the angle enclosed by the saturation magnetization and the easy axis directions of soft magnetic layer.However,it is unsensitive to the easy axis direction of hard magnetic layer,but there exists a maximum remanence for a certain easy axis direction of hard magnetic layer.     

正交各向异性双层交换弹簧薄膜的磁矩分布

本文以Pt_(84)Co_(16)/TbFeCo双层交换弹簧体系为研究对象,利用微磁学连续模型,研究了软/硬磁层易轴方向相互垂直的新型体系中磁矩的分布特征.研究结果表明,磁矩偏离薄膜法线方向的角度在软磁层中沿膜厚方向的变化速率比硬磁层中的快.通过调节软磁层参数来增加软/硬磁的各向异性常数比、交换能常数比、饱和磁化强度比或外磁场强度,都可有效改变磁矩偏角在软/硬磁层中的变化速率.特别是当软/硬磁各向异性常数比值和交换能常数比值同时增大时,可以使得磁矩在硬磁层中的变化速率快于软磁层中的.而饱和磁化强度比值对磁矩变化速率的影响源于饱和磁化强度的变化会相应地改变各向异性常数,进而改变磁矩在软/硬磁层中磁矩方向变化速率的比值.此体系的磁滞回线显示磁性参数的改变可以显著改变体系的剩磁及饱和磁场.软磁层中的退磁场能及体系的正交各向异性可导致负的成核场.     

Magnetization reversal in CoPt-based hard–soft homocomposites

CoPt-based hard–soft sputtered bilayers with (1 1 1) texture have been produced by appropriate heat treatment of the bottom layer. Two samples with different degrees of chemical ordering of the hard layer are compared. The anisotropy of the hard layer determines its robustness against destabilization from the soft one. Detailed measurements of the soft layer minor hysteresis loop features as a function of the magnetic state of the hard layer are proposed as a means to study the nature of interfacial exchange interactions and the mechanism of magnetization reversal. When hard layer anisotropy is not robust enough, the reversed soft layer can induce irreversible changes to the magnetic structure at the interface leading to a decoupling of exchange field from the magnetic state of the hard layer.     

Field induced biquadratic exchange in hard/soft ferromagnetic bilayers

The appearance of biquadratic exchange coupling between soft Fe and hard SmCo thin layers is found. The remanent magnetization in the Fe layer reorients from parallel to perpendicular with respect to the SmCo easy axis after application of large enough negative field. To explain such an unexpected behavior in contacting ferromagnetic layers a model is proposed based on Slonczewski's fluctuating exchange mechanism. In our samples a partial remagnetization of the hard layer creates fluctuations of the bilinear interactions. The intralayer exchange averaging of the resulting magnetization fluctuations in the soft layer causes the observed biquadratic coupling.     

Magnetic properties of Co-P-based trilayers

The magnetic properties of a film trilayer consisting of hard magnetic and soft magnetic Co-P layers separated by a nonmagnetic Ni-P spacer have been studied. The features of the hysteresis shift relative to the zero exchange magnetic field and of the coercivity of the soft magnetic layer in the dependence on thicknesses of the hard magnetic layer and spacer have been considered. The dynamic changes in the shift of the hysteresis of the soft magnetic layer versus the magnetization reversal time after saturation of the hard magnetic layer have been found and investigated.     

Oscillatory decay of magnetization induced by domain-wall stray fields

The demagnetization of a hard ferromagnetic layer via the fringing fields of domain walls created by reversing the moment of a neighboring soft ferromagnetic layer is explored experimentally. An unusual oscillatory decay of the magnetic moment of the hard layer is observed using structures in which the demagnetization occurs after a few hundred cycles. This surprising observation is confirmed on a microscopic scale by detailed imaging of the magnetization of the hard layer using high resolution photoemission electron microscopy and by micromagnetic simulations.     

Biased magnetization reversal in bi-phase multilayer microwires

We report on the magnetic behaviour of a novel family of two-magnetic-phase multilayer microwires consisting of: (i) a bistable FeSiB glass-coated amorphous microwire as soft nucleus, and (ii) a polycrystalline CoNi outer microtube as harder layer. Such bi-phase microwires are prepared by combined quenching and drawing plus sputtering and electroplating techniques. The stray field produced by the harder outer layer after premagnetizing it to saturation is used to bias the magnetization reversal process of the soft nucleus via dipolar magnetostatic coupling. A detailed analysis of the asymmetric low-field magnetization reversal process of the soft nucleus is presented together with the study of the fluctuating switching field and its asymmetric behaviour. The study of the domain wall characteristics under the presence of a nucleation coil at one end of the microwire allows us to draw conclusions on the role of the bias field generated by the premagnetized hard outer layer.     

Magnetic tuning of biquadratic exchange coupling in magnetic thin films

The effective interlayer coupling between antiferromagnetically coupled hard and soft ferromagnetic thin films is investigated as a function of the magnetic bit length in the hard layer, which is controlled using a magnetic recording system. The interlayer coupling is explored by studying the magnetization reversal of the soft layer. As the bit length decreases, the coupling evolves from antiferromagnetic to biquadratic to uncoupled. These results are reproduced using a micromagnetic model and determine the applicability range of Slonczewski's fluctuation model of biquadratic coupling.     

Synthesis and magnetic properties of (CoNiPsoft/CoPhard) n multilayers

Magnetic interactions in Co-Ni-P multilayers consisting of alternating magnetically soft and magnetically hard layers are investigated experimentally. Variations in the shape of magnetization hysteresis loops upon the conjugation of magnetically soft and hard layers are found, along with saturation field oscillations that depend on the number of layer pairs.     

Remanence characteristic of nanostructure of hard/soft magnetic multilayered systems with random easy axis orientations

The macroscopic magnetic properties such as remanent magnetization of the ferromagnetic multilayer system with random easy axis orientations is investigated by using a effective micromagnet approach. The multilayer, which alternating soft/hard layers in which their easy axis orientations is random build a nanostructured multilayer, is considered to meet periodic boundary condition, the dependence of remanence on thickness has been analytical derived. Author find that the remancence clearly depends on the thickness of the soft magnetic layer nearly independence of thickness of hard magnetic layer. this analytical results are in excellent agreement with previous numerical results.     

Monte Carlo study of magnetization reversal in the model of a hard/soft magnetic bilayer

Magnetization reversal in the model of a hard/soft magnetic bilayer under the action of an external magnetic field has been investigated by the Monte Carlo method. Calculations have been performed for three systems: (i) the model without a soft-magnetic layer (hard-magnetic layer), (ii) the model with a soft-magnetic layer of thickness 25 atomic layers (predominantly exchange-coupled system), and (iii) with 50 (weak exchange coupling) atomic layers. The effect of a soft-magnetic phase on the magnetization reversal of the magnetic bilayer and on the formation of a 1D spin spring in the magnetic bilayer has been demonstrated. An inf lection that has been detected on the arch of the hysteresis loop only for the system with weak exchange coupling is completely determined by the behavior of the soft layer in the external magnetic field. The critical fields of magnetization reversal decrease with increasing thickness of the soft phase.     

Effect of the soft layer thickness on magnetization reversal process of exchange-spring nanomagnet patterns

A systematic study of the magnetization reversal behavior in the regular arrangement of L1₀-FePt based exchange-spring nanomagnets with different thicknesses of the Co soft magnetic layer is presented. The magnetic property of the hard magnet is compared to two tuned exchange-spring magnets: its systems of 20 nm L1₀-FePt/3 nm, and 7 nm Co. In particular, we focus on the switching field distribution. The exchange coupling showed narrower SFD, in spite of the decoupled part switches earlier. The magnetization switching mechanism of exchange-spring nanomagnets patterns has been revealed with a first-order reversal curves technique and the switching field distribution. Further, the microscopic results using magnetic force microscopy show that the spin rotation of the non-interacting part in the thicker soft layered exchange-spring magnet. The part influences the magnetization reversal process. According to the experimental results, exchange coupling strength can be tuned by the thickness of the soft magnetic layer.     

Coercive force and magnetization reversal of Co—P Films obtained by chemical deposition

Results from studying three-layer films with magnetic layers produced on the basis of the Co—P compound and a nonmagnetic Ni—P layer are presented. It is shown that the features of the magnetization reversal of the film are due to the kinetics of the formation of the crystalline structure of the hard magnetic layer. It is established that at low thickness, this layer consists of separate grains of the crystalline phase. With an increase in thickness, this layer transitions to the homogeneous polycrystalline state. These results allow us to explain the anomalous change of the coercive force and the displacement field of the soft magnetic layer depending on the thickness of the hard magnetic layer.     

Enhanced nucleation fields due to dipolar interactions in nanocomposite magnets

One approach to construct powerful permanent magnets while using less rare-earth elements is to combine a hard magnetic material having a high coercive field with a soft magnetic material having a high saturation magnetization at the nanometer scale and create so-called nanocomposite magnets. If both materials are strongly coupled, exchange forces will form a stable magnet. We use finite element micromagnetics simulations to investigate the changing hysteresis properties for varying arrays of soft magnetic spherical inclusions in a hard magnetic body. We show that the anisotropy arising from dipolar interactions between soft magnetic particles in a hard magnetic matrix can enhance the nucleation field by more than 10% and strongly depends on the arrangement of the inclusions.     

Effect of the effective anisotropy field of soft layer on magnetic properties of soft/hard stacked media

Magnetic properties of soft/hard stacked perpendicular magnetic recording media were investigated using a two-moment model with taking account of demagnetizing energy. Demagnetizing energy of the soft layer may improve the uniformity of magnetic properties of the composite media and also decrease the interlayer thickness, although weaken the thermal stability a little. The application of high saturation magnetization (M_s) soft magnetic material as the soft layer may compensate for the undesirable contribution while maintaining its benefits.     

Layer resolved magnetization reversal study in SmCo5/Fe nanocomposite bilayers

A hard/soft SmCo5/Fe nanocomposite magnetic bilayer system is fabricated on x-ray transparent 100-200 nm thin Si3N4 films by magnetron sputtering.The microscopic magnetic domain pattern and its behaviours during magnetization reversal in the hard and the soft magnetic phases are studied separately by element specific magnetic soft x-ray microscopy at a spatial resolution of better than 25 nm.We observe that the domain patterns for the soft and hard phases show coherent behaviours in varying magnetic fields.We derive local M(H) curves from the images of Fe and SmCo5 separately and find the switches for hard and soft phases to be the same.     

纳米晶永磁Pr8Fe87B5反磁化机理研究

用熔体快淬法制备了Pr2Fe14B/α-Fe纳米复合永磁样品.测量了样品的起始磁化、反磁化过程、矫顽力和剩磁与外场的关系，以及样品的磁粘滞性.经分析认为材料的矫顽力主要由非均匀的钉扎机理决定，但由于交换硬化的软磁相的可逆转动使得这种反磁化机理不同于单相永磁材料的钉扎行为.磁粘滞性表明热激活主要源于硬磁相的不可逆磁化行为. 关键词： 纳米复合永磁 矫顽力 剩磁 磁粘滞     

Hard layer demagnetization by soft layer cycling in a MgO-based perpendicular magnetic tunnel junction

We report here that in perpendicular tunnel junction the hard layer demagnetizes when the soft layer is cycled. This happens faster when the cycling field is closer to the reversal field of the hard layer. Magnetic force microscopy imaging done at different stages of the cycle after several loops show compact demagnetized areas surrounded by large saturated zones in the hard layer. A mechanism based on interlayer magnetostatic coupling induced by the stray field created by domain wall in the soft layer is presented.     

Experimental evidence of dipolar interaction in bilayer nanocomposite magnets

We use magnetic thin film hard/non/soft-magnetic trilayer systems to probe the nature of the hard–soft phase interaction and the role played by dipolar fields in one-dimensional (d) magnetic systems. We have systematically investigated six wedge samples where the thickness of a Cu spacer layer (t _Cu) was gradually changed to create a varying interfacial effect on the interaction between a CoPt hard layer and a Fe soft layer. Magneto-optical Kerr effect was used to obtain the magnetization loops at 28 points on each sample, and the nucleation field (H _N ) as a function of t _Cu was employed to characterize the layer interaction as a function of t _Cu. H _N (t _Cu) show a RKKY oscillatory behavior in addition to a non-negligible dipolar contribution, which had an exponential dependence. The dipolar term, which cannot be always neglected, is affected by the interface roughness and also by the CoPt crystallinity. Therefore, we cannot always consider exchange coupling to be the dominant interaction in one-d hard–soft magnetic bilayer systems, particularly, during magnetic reversal.