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Development of Magnetic Nanopartides with High Surface Anisotropy for High Density Recording

用于高密度记录的高表面各向异性磁性纳米粒子的开发

基本信息

批准号：
13650331
负责人：
KITAKAMI Osamu
金额：
$ 2.3万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650331/
关键词：
magnetic memory nanoparticles thermal agitation surface anisotropy magnetic recording hydrogenation

项目摘要

We have studied magnetic surface anisotropy (MSA) at 3d transition metals (TM)/Pd, Pt, SiO_2 interfaces, and investigated the surface effect on the effective magnetic anisotropy of nanopartocles.1. MSA at TM/Pd, Pt, interfaces The MSA strongly depends on the valence electron number of TM and reaches a maximum of 〜0.5 erg/cm^2 for TM = Co, which is consistent with the first principles calculation so far reportd. R is also found that addition of very small amount of rare earth elements (RE) into TM omsiderahly enhanoes the MSA due to the enhancement of orbital moment of Co.2. MSA at TM/nonmagnetic oxide (SiO_2) The MSA at TM/SiO_2 strongly depends on the valence electron number of TM. With increasing the valence electron number from TM = Fe, Co to Ni the easy axis changes from the film normal to the film plane. The maximum perpendicular anisotropy reaches 0.4〜0.8 erg/cm2 for TM = Fe, Co, which is one order of magnitude higher than the magnetocrystalline anisotropy of bulk bcp Co. The dep … More endence of the MSA on the valence electron number of TM has been successfully explained by considering the electronic states of TM combined with SiO_2 at the interface.3. MSA in TM/ nonmagnetic oxide granular films It is found that Fe/SiO_2 granular films (Fe particle size 5〜30 nm) exhibit very high coercibity of Hc〜500 Oe which is much higher than the anisotropy field (〜100 Oe) of bulk bccFe. By considering the measured MSA of 0.4 erg/cm^2 for Fe/SiO_2 we have quantitatively explained their large Hc and the particle size dependence. This result indicates that MSA effectively enhances the magnetic anisotropy of nanoparticles embedded in granular films.4. MSA in TM nanoparticles We have prepared isolated TM (Fe, Co, Ni) nanopartides with the diameter of D = 5〜30 nm and determined their magnetic anisotropy by the newly developed anisotropy measurement method. It is found that all the nanoparticles exhibit strong uniaxial magnetic anisotropy compared with that of bulk materials. Such anisotropy enhanoement is mainly due to the surface effect. From the micromagnetic calculations and experiments, we have confirmed that the magnetic behaviors of the nanopartivles perfectly follows the coherent rotation (Stoner Wohlfarth) model when the particle diameter Dis less than 15 nm.All the results mentioned above indicate that magnetic surface anisotropy significantly enhanoes the effective magnetic anisotropy of nanopartocles even when the bulk anisotropy is quite small. Such nanoparticles with large surface anisotropy would be very promising for development of ultra high density recording media. Less

我们研究了3d过渡金属(TM)/Pd，Pt，SiO_2界面的磁表面各向异性(MSA)，并研究了表面效应对纳米材料有效磁各向异性的影响。在Tm/Pd，Pt，界面的MSA强烈依赖于Tm的价电子数，并且在Tm=Co时达到最大值~0.5erg/cm^2，这与迄今报道的第一性原理计算是一致的。R还发现，在Tm中加入极少量的稀土元素(RE)，由于增加了Co2的轨道矩，使MSA增强。Tm/非磁性氧化物(SiO_2)的MSA与Tm/SiO_2的价电子数密切相关。随价电子数从Tm=Fe，Co到Ni的增加，易轴由薄膜垂直向薄膜平面转变。当Tm=Fe，Co时，最大垂直各向异性达到0.4~0.8erg/cm~2，比块体BCP Co的磁晶各向异性高一个数量级。DEP…通过考虑Tm与SiO_2在界面结合的电子态，成功地解释了MSA对价电子数的影响。在TM/非磁性氧化物颗粒膜中发现，Fe/SiO_2颗粒膜(Fe颗粒尺寸为5~30 nm)具有很高的矫顽力Hc~500Oe，远高于块体BccFe的各向异性场(~100Oe)。考虑到Fe/SiO_2的测量MSA为0.4erg/cm~2，我们定量地解释了它们较大的Hc和颗粒大小的依赖关系。这一结果表明，MSA有效地增强了镶嵌在颗粒膜中的纳米颗粒的磁各向异性。我们制备了直径为5~30 nm的孤立的Tm(Fe，Co，Ni)纳米粒子，并用新发展的各向异性测量方法测定了它们的磁各向异性。结果表明，与块体材料相比，所有纳米粒子都表现出较强的单轴磁各向异性。这种各向异性增强主要是由表面效应引起的。从微磁计算和实验证实，当纳米粒子直径D<15 nm时，纳米粒子的磁行为完全符合相干旋转(Stoner Wohlfarth)模型。上述结果表明，即使在体积各向异性很小的情况下，磁表面各向异性也显著地增强了纳米粒子的有效磁各向异性。这种具有大表面各向异性的纳米粒子在超高密度记录介质的开发中具有很好的应用前景。较少