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1.
本文就纳米复合永磁材料中软磁相被交换硬化问题,从一维模型和三维模拟计算进行了分析研究. 一维和三维各向异性样品研究表明,在相同微结构下,当硬磁相的各向异性降低时,除矫顽力降低外,在磁矩全部反转之前退磁曲线是一样的. 因此,硬磁相各向异性的降低不会导致最大磁能积(BH)max增大和剩磁增加. 对于三维各向同性样品的模拟计算表明,降低硬磁相的各向异性会使剩磁和(BH)max都明显降低. 因此,增强硬磁相的各向异性并增大硬磁相晶粒尺寸是提高 关键词: 纳米复合永磁 矫顽力 剩磁 磁能积  相似文献   

2.
高性能纳米复合永磁材料的模拟计算研究   总被引:5,自引:0,他引:5       下载免费PDF全文
张宏伟  荣传兵  张绍英  沈保根 《物理学报》2004,53(12):4347-4352
构造了在软磁相基体中析出规则形状硬磁相的各向同性和各向异性纳米复合永磁材料Pr2Fe14Bα-Fe.利用微磁学的有限元法,模拟计算了样品的磁滞回线.通过对剩磁、矫顽力和最大磁能积与软磁相厚度的关系分析,发现在软磁相厚度为0—12nm的范围内,复合磁体的矫顽力随软磁相厚度的增加而单调下降,而最大磁能积则是在适当的矫顽力和剩磁下达到最高.预计纳米复合Pr2(Fe,Co)14Bα-(Fe,Co)的各向同性磁体的最大磁能积最高可达248kJ/m3,而各向异性磁体则高达784kJ/m3. 关键词: 纳米复合永磁 矫顽力 剩磁 磁能积  相似文献   

3.
用熔体快淬法制备了纳米复合永磁样品Pr9Fe74Co12B5 与Pr9Fe74Co12B5Sn0.5,分析了样品的起始磁化、反磁化过程,测得样品的总磁化率、可逆磁化率以及样品的磁黏滞性.结果表明,两样品在室温下均表现为单一硬磁相磁化行为,在低温下表现为双相行为,且由于添加Sn后使晶粒均匀化从而导致样品低温下的双相行为更加明显.添加Sn后引起样品中软磁相含量和软磁相晶粒尺寸的增加,使磁化反转中可逆磁化部分增多,且使反磁化形核场降低.磁黏滞性研究表明,热激活体积与软磁相晶粒的大小有关. 关键词: 纳米复合永磁 磁化反转 磁粘滞  相似文献   

4.
铁基纳米复合永磁材料的相成分与磁性   总被引:4,自引:0,他引:4  
成昭华  沈保根 《物理》1997,26(5):272-279
纳米复合永磁材料由于具有高剩磁,高磁能积,高矫顽力和相对低的稀土含量等优点而有可能成为新一代价格低谦粘结永磁体,文章介绍了纳米复合永磁材料的磁特性,着重讨论了Fe3B基纳米材料相成分与磁性的关系,并证明其永磁性并非来源于Nd2Fe14B永磁相,最后介绍了纳米复合永磁材料的最新进展。  相似文献   

5.
敖琪  张瓦利  张熠  吴建生 《物理学报》2005,54(10):4889-4893
利用磁控溅射法制备了Nd28Fe66B6/Fe50Co50 双层纳米复合磁性薄膜,研究了其结构和磁性.经873K退火处理15min 后,利用x射线衍射仪测定薄膜晶体结构,采用俄歇电子能谱仪估算薄膜厚度和超导量子干 涉仪测量其磁性.磁性测量表明,1)该系列薄膜具有垂直于膜面的磁各向异性.从起始磁化曲 线和小回线的形状特征可知,矫顽力机制主要是由畴壁钉扎控制.2)对于固定厚度(10nm) 层的硬磁相Nd-Fe-B和不同厚度(dFeCo=1—100nm)层软磁相FeCo双层纳米复合 膜,剩磁随软磁相FeCo 厚度的增加快速增加,而矫顽力则减少.当dFeCo=5nm 时 ,最大磁能积达到160×10A/m.磁滞回线的单一硬磁相特征说明,硬磁相Nd -Fe-B层和软磁相FeCo层之间的相互作用使两相很好地耦合在一起.剩磁和磁能积的提高是由 于两相磁性交换耦合所致. 关键词: Nd-Fe-B/FeCo双层纳米复合膜 交换耦合 磁性增强  相似文献   

6.
稀土永磁体即使内秉性质相同,但矫顽力可能相差很大.本文以Pr-Fe-B磁体为例,从热激活反磁化即反磁化临界过程探讨决定矫顽力的关键因素.Pr-Fe-B晶粒表层缺陷区与晶粒内部耦合推动反磁化畴形核从而去钉扎,晶粒表层缺陷区的各向异性对克服晶粒内部势垒具有贡献,因此反磁化形核场和矫顽力大大降低.由于晶粒表层缺陷区与晶粒内部耦合,在反磁化临界过程磁畴壁尺寸稍大于理论尺寸.具有软、硬磁相结构的Pr-Fe-B复合磁体,软、硬磁相晶粒之间交换耦合作用也会增大反磁化畴壁尺寸.软、硬磁交换耦合的能量对克服硬磁相晶粒内部各向异性势垒也会有贡献,这将进一步降低磁体矫顽力.添加Ti,Nb高熔点金属,复合磁体矫顽力显著提高.分析认为,这不仅仅是磁体晶粒尺寸减小的缘故.热激活尺寸减小说明磁畴壁中包含的硬磁相晶粒表层缺陷区尺寸减小,硬磁相表面和两相界面各向异性对克服硬磁相晶粒内部势垒的贡献减小,反磁化所需外磁场增大.  相似文献   

7.
用熔体快淬法制备了纳米复合永磁样品Pr9Fe74Co12B5与Pr9Fe74Co12B5Sn0.5,分析了样品的起始磁化、反磁化过程,测得样品的总磁化率、可逆磁化率以及样品的磁黏滞性.结果表明,两样品在室温下均表现为单一硬磁相磁化行为,在低温下表现为双相行为,且由于添加Sn后使晶粒均匀化从而导致样品低温下的双相行为更加明显.添加Sn后引起样品中软磁相含量和软磁相晶粒尺寸的增加,使磁化反转中可逆磁化部分增多,且使反磁化形核场降低.磁黏滞性研究表明,热激活体积与软磁相晶粒的大小有关.  相似文献   

8.
Nd28Fe66B6/Fe50Co50双层纳米复合膜的结构和磁性   总被引:2,自引:0,他引:2       下载免费PDF全文
利用磁控溅射法制备了Nd28F66B6/Fe50Co50双层纳米复合磁性薄膜,研究了其结构和磁性.经873K退火处理15min后,利用x射线衍射仪测定薄膜晶体结构,采用俄歇电子能谱仪估算薄膜厚度和超导量子干涉仪测量其磁性.磁性测量表明,1)该系列薄膜具有垂直于膜面的磁各向异性.从起始磁化曲线和小回线的形状特征可知,矫顽力机制主要是由畴壁钉扎控制.2)对于固定厚度(10nm)层的硬磁相Nd-Fe-B和不同厚度(dFeCo=1-100nm)层软磁相FeCo双层纳米复合膜,剩磁随软磁相FeCo厚度的增加快速增加,而矫顽力则减少.当dFeCo=5nm时,最大磁能积达到160×103A/m.磁滞回线的单一硬磁相特征说明,硬磁相Nd-Fe-B层和软磁相FeCo层之间的相互作用使两相很好地耦合在一起.剩磁和磁能积的提高是由于两相磁性交换耦合所致.  相似文献   

9.
烧结Nd-Fe-B永磁合金矫顽力机制的理论与实验研究   总被引:2,自引:0,他引:2       下载免费PDF全文
从理论和实验上研究了烧结Nd-Fe-B永磁合金的矫顽力随取向磁场的变化规律。指出磁体反磁化过程主要是晶粒边界软磁性区的反磁化成核以及反磁化核长大成畴并向晶粒内部不可逆畴壁位移的过程。比较了成核场与退钉扎场的大小及其随磁场方向的变化,并得出结论:退钉扎场是决定烧结Nd-Fe-B磁体矫顽力的主要机制。 关键词:  相似文献   

10.
高汝伟  周寿增 《物理学报》1994,43(1):146-153
从理论和实验上研究了烧结Nd-Fe-B永磁合金的矫顽力随取向磁场的变化规律。指出磁体反磁化过程主要是晶粒边界软磁性区的反磁化成核以及反磁化核长大成畴并向晶粒内部不可逆畸壁位移的过程。比较了成核场与退钉扎场的大小及其随磁场方向的变化,并得出结论:退钉扎场是决定烧结Nd-Fe-B磁体矫顽力的主要机制。  相似文献   

11.
The magnetic properties of an isotropic, epoxy resin bonded magnets made from Pr-Fe-Co-Nb-B powder were investigated. The magnetization reversal process and magnetic parameters were examined by measurements of the initial magnetization curve, major and minor hysteresis loops and sets of recoil curves. From the initial magnetization curve and the field dependencies of the reversible and irreversible magnetization components derived from the recoil loops it was found that the magnetization reversal process is the combination of the nucleation of reversed domains and pinning of domain walls at the grain boundaries and the reversible rotation of magnetization vector in single domain grains. The interactions between grains were studied by means of δM plots. The nonlinear behavior of δM curve approve that the short range intergrain exchange coupling interactions are dominant in a field up to the sample coercivity.The interaction domains and fine magnetic structure were revealed as the evidence of exchange coupling between soft α-Fe and hard magnetic Nd2Fe14B grains.  相似文献   

12.
The aftereffect field of thermal activation,which corresponds to the fluctuation field of a domain wall,is investigated via specific measurements of the magnetization behavior in Pr2Fe14B nanocrystalline magnets.The thermal activation is a magnetization reversal arising from thermal fluctuation over an energy barrier to an equilibrate state.According to the magnetic viscosity and the field sweep rate dependence of the coercivity,the calculated values of the fluctuation field are lower than the aftereffect field and in a range between those of domain walls and individual grains.Based on these results,we propose that the magnetization reversal occurs in multiple ways involving grain activation and domain wall activation in thermal activation,and the thermal activation decreases the coercivity by~0.2 kOe in the Pr2Fe14B ribbons.  相似文献   

13.
Hard/soft-magnetic composite pillar array medium is proposed for ultra-high-density recording media. Magnetization reversal process for a single hard/soft-magnetic composite pillar in the medium is calculated using the Landau–Lifshitz–Gilbert equation. Magnetization reversal of the soft-magnetic unit helps the magnetization reversal for the hard-magnetic unit, and the effective coercivity for the hard-magnetic unit is greatly reduced. Thereby saturation recording to the high-Ku-hard-magnetic material used for perpendicular magnetic recording will be realizable.  相似文献   

14.
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.  相似文献   

15.
We have investigated the evolution of the magnetization reversal mechanism in asymmetric Ni nanowires as a function of their geometry. Circular nanowires are found to reverse their magnetization by the propagation of a vortex domain wall, while in very asymmetric nanowires the reversal is driven by the propagation of a transverse domain wall. The effect of shape asymmetry of the wire on coercivity and remanence is also studied. Angular dependence of the remanence and coercivity is also addressed. Tailoring the magnetization reversal mechanism in asymmetric nanowires can be useful for magnetic logic and race-track memory, both of which are based on the displacement of magnetic domain walls. Finally, an alternative method to detect the presence of magnetic drops is proposed.  相似文献   

16.
For FeCr/IrMn bilayers, the exchange bias training effect and the magnetization reversal mechanism are correlated to each other and depend on the composition of the ferromagnetic layer. For high Fe contents, the asymmetric magnetization reversal is observed. During the training effect, both exchange field and coercivity decrease monotonically, suggesting a type I training effect. For low Fe contents, the domain wall depinning takes place for the two hysteresis loop branches. Only exchange field diminution happens in the training effect. The coercivity almost does not change in the process, corresponding to a type II training effect. It is suggested that the motion of antiferromagnetic spins is modified by the magnetization reversal mechanism in the ferromagnetic layer.  相似文献   

17.
Exchange biasing was studied in an exchange-spring system consisting of two ferrimagnetic films with different coercivity. Magnetite and Co-Fe ferrite were chosen as the soft and hard magnetic bilayer components, respectively. The samples were epitaxially grown on MgO single crystal substrates by pulsed laser deposition. The exchange-bias field was investigated as a function of system size and shape, magnetic field direction and magnetization reversal in the hard layer. A clear dependence of the exchange-bias field on the sample size and shape was found. This was attributed to an interplay between exchange and dipolar energies. Micromagnetic simulations agree with the experimental results.  相似文献   

18.
CoCr metallic films are widely investigated as recording media with vertical anisotropy. This media is not yet completely characterized especially with regard to the magnetization reversal process. It is argued here that measurements of the angular dependence of the coercivity and remanence coercivity are completely consistent with incoherent reversal processes.  相似文献   

19.
用电弧熔炼法制备了Nd3.6Pr5.4Fe83Co3B5合金铸锭,然后利用熔旋快淬法在铜辊转速V=20m/s下制备了Nd3.6Pr5.4Fe83Co3B5薄带.快淬带主要由软磁相α-Fe和Nd2Fe14B型的硬磁相组成.采用直流退磁剩磁曲线方法分析了样品在反磁化过程中的可逆与不可逆磁化部分,并研究了软磁相和硬磁相的反磁化行为,得到样品的不可逆磁化形核场Hno约为440kA/m.同时研究了样品的磁黏滞性,结果表明由于软磁相的存在使得热激活体积较大. 关键词:  相似文献   

20.
Hysteresis loops and magnetic reversal processes have been determined by a three dimensional (3D) micromagnetic model for exchange-coupled Nd2Fe14B/α-Fe bilayers and carefully compared with a popular one-dimensional (1D) micromagnetic model. It is found that the calculated hysteresis loops, the critical fields and the magnetic phase diagrams agree well with the results given by the 1D model. However, the calculated nucleation mode is a quasi-curling one where the magnetic moment exhibits a curling in the film plane and varies in the thickness direction, in contrast with the reported quasi-coherent mode. The calculated spatial distribution of the magnetization orientation in the thickness direction at various applied fields signifies a three-step magnetic reversal process, which includes nucleation, growth and displacement of the domain wall as well as the rotation and the reversal of magnetization in the hard phase. The magnetic reversal of the hard phase is much slower than that given by the 1D model, leading to a more slant hysteresis loop near the coercivity point.  相似文献   

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