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MAGNETIC PROPERTIES OF REGULARLY ARRAYED NANODOTS AND THEIR APPLICATION TO ULTRA-HIGH DENSITY

规则排列纳米点的磁性及其在超高密度中的应用

基本信息

批准号：
13555087
负责人：
KITAKAMI Osamu
金额：
$ 7.94万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

In a future ultra-high density magnetic memory, the size of each memory bit will be reduced down to 10×10 nm^2, indicating that each bit consists of one nanoparticle. Therefore, the magnetization reversal process and thermal stability of each nanoparticle have to be clarified for development for the future magnetic memory. However, it has been difficult to measure the magnetic properties of such a nanoparticle because of the very poor sensitivity of 10^<-6> emu for conventional magnetometers. To overcome this difficulty, we have developed a very sensitive Hall effect method for a very small nanoparticle. The sensitivity reaches 〜 10^<-14> emu for FePt. By using this technique, we have investigated the magnetic properties and thermal stability of a single crystal L1_0-FePt (001) nanodot by patterning an well characterized epitaxial film. For the particle diameter of D_m < 20 nm, all the magnetic properties, such as the angular dependence of the irreversible switching field H_r, the magn … More itude of coercivity H_c, and their temperature dependences, are completely explained by the coherent rotation model (Stoner-Wohlfarth model) taking thermal relaxation into account. As the particle size D_m exceeds 20 nm, the magnetic behaviors obviously deviate from the coherent rotation model, indicating that the magnetization reversal mode changes from coherent to incoherent rotation modes. For this incoherent region, the activation energy has been evaluated to be about 10^<-12> erg regardless of the dot size, which is much smaller than the product of the anisotropy energy and dot volume but nearly equal to γδ^2 (γ: domain wall energy density, δ: wall width), suggesting that the magnetization reversal is initiated by nucleation of a reversed embryo with the dimension of the exchange length. The critical diameter D_m 〜 20 nm at which the reversal mode changes almost agrees with the critical diameter predicted by the micromagnetic theory. Based on these results, we have successfully designed the detail specifications for a prospective ultra-high density magnetic memory with the area density of 1 terabits/inch^2. Less

在未来的超高密度磁存储器中，每个存储比特的尺寸将减小到10×10 nm^2，表明每个比特由一个纳米粒子组成。因此，每个纳米粒子的磁化反转过程和热稳定性都必须得到澄清，以便为未来的磁记忆研究奠定基础。然而，由于传统磁力计的10^-6&gt；EMU灵敏度很低，很难测量这种纳米颗粒的磁性。为了克服这一困难，我们开发了一种非常灵敏的霍尔效应方法来测量非常小的纳米粒子。对FePT的灵敏度可达~10^&lt；-14；emu。利用这一技术，我们研究了单晶L1_0-FePT(001)纳米点的磁性和热稳定性。对于粒径为20 nm的Dm和Lt；，所有的磁性质，如不可逆开关场H_r的角度依赖关系，Magn…考虑热弛豫的相干旋转模型(Stoner-Wohlfarth模型)完全解释了更多的矫顽力Hc及其与温度的关系。当颗粒尺寸Dm大于20 nm时，磁性行为明显偏离相干旋转模型，表明磁化反转模式由相干旋转模式转变为非相干旋转模式。对于这个非相干区，无论点的大小，激活能都约为10^-lt；-12；erg，这比各向异性能量与点体积的乘积小得多，但几乎等于γδ^2(γ：磁化壁能密度，δ：壁宽)，这表明磁化反转是由交换长度尺寸的反转胚胎成核引起的。反转模变化的临界直径D_m~20 nm与微磁理论预测的临界直径基本一致。基于这些结果，我们成功地设计出了面密度为1太比特/英寸^2的未来超高密度磁存储器的详细技术指标。