高密度磁记录纳米颗粒膜磁性的蒙特—卡罗模拟

Monte-Carlo Modeling of Magnetic Properties in Magnetic Granular Film for High density Recording

用蒙特-卡罗方法对Co-C和CoPt-C纳米颗粒膜的磁特性进行模拟研究. 模拟中,假设磁性颗粒为球形、单畴,易轴随机取向. 对包含hcp结构、直径为3 nm的Co颗粒的Co-C膜给出了湿度从3 K到300 K的磁滞回线,超顺磁驰豫的截止温度约20 K;对包含fct结构CoPt的CoPt-C膜给出了300 K时平均颗粒尺寸从4 nm到6 nm,对应于不同尺寸分布下的磁滞回线. 模拟显示,由于fct结构CoPt-C有特大的各向异性,因而具备超高的矫顽力,可以满足超高密度磁记录的需要. 以上模拟的结果与Co-C颗粒膜和CoPt-C颗粒膜的实验结果一致.

In this paper, magnetic properties of Co-C and CoPt-C nanogranular films are modeled using the Monte Carlo method. Each grain in the films is assumed to be spherical in shape, with a single domain and a random crystalline easy axis in the model. For Co-C films, the hysteresis loop for hexagonal close-packed (hcp) Co grains of 3 nm in size is calculated at various temperatures ranging from 3 K to 300 K. The superparamagnetic relaxation blocking temperature (Tb) is demonstrated to be about 20 K. For CoPt-C films, hysteresis magnetization calculations are performed on face-central- tetragonal (fct) CoPt inter-metal compound grains encapsulated in carbon with various grain sizes ranging from 4 nm to 6 nm and different distributions. Extremely high coercivities required by ultra-high density magnetic recording are achieved in these films owing to the very large anisotropy of fct CoPt compound. The numerical results are compared with our experimental data of Co-C granular films and those of CoPt-C granular films recently reported in the literature.