Co-C纳米复合薄膜的微结构、磁性能和磁输运特性

MICROSTRUCTURE,MAGNETIC AND MAGNETOTRANSPORT PROPERTIES OF Co-C NANOCOMPOSITE THIN FILMS

采用磁控溅射法在硅基片上制备了Co原子分数为13.0%的Co-C纳米复合薄膜.在真空条件下,对薄膜进行退火处理,退火温度从473K逐步提高至773K,保温时间30min.形貌观察表明,未经退火处理的薄膜中,Co颗粒均匀分布在非晶C基体中,Co颗粒尺寸为1.5-3.0nm;673K退火后,Co颗粒尺寸增大.磁性能测试表明,未经退火处理的薄膜磁性较弱,随着退火温度升高,薄膜的磁化强度和矫顽力均明显增大;当退火温度增加至673—773K时,薄膜呈现出低温铁磁性、室温超顺磁性的典型颗粒体系磁性特征.磁输运特性研究表明,未经退火处理的薄膜在温度为4.2K,磁场为3980kA/m时表现出1.33%的负磁电阻,随着退火温度升高,样品磁电阻值下降;电阻与温度关系在4.2—60K范围内符合lnR-T^(-1/4)线性关系,磁输运遵循变程跳跃(variable range hopping)传导机制.

Co-C nanocomposite thin films with a Co atomic content of 13.0%were fabricated onto Si（100） substrates by magnetron co-sputtering technique.Post annealing was carried out in vacuum at annealing temperature ranging from 473 K to 773 K for 30 min.TEM images indicate that the Co nanoparticles are dispersed uniformly in an amorphous carbon matrix for the as-deposited samples,and Co particle size is in a range of 1.5—3.0 nm.After annealing at 673 K,the average Co particle size is enlarged distinctly.Magnetization hysteresis loops reveal that the as-deposited thin films show low magnetization.As annealing temperature is increased,both magnetization and coercivity are enhanced significantly.The samples annealed at 673 K and 773 K show ferromagnetic behaviors at low temperature,and superparamagnetic behaviors at room temperature, which are characteristic magnetic features for granular system.A negative magnetoresistance（MR） of 1.33%is observed for the as-deposited Co-C thin films at 4.2 K in the applied magnetic field of 3980 kA/m.The MR value decreases with increasing annealing temperature.Resistance（R） versus temperature（T） curves exhibit a good linear relationship of InR-T^（-1/4） at a broad low temperature range,suggesting that the conduction in Co-C nanocomposite thin films follows the variable range hopping transport mechanism.