Investigation of the static and dynamic magnetic properties of CoFe2O4 nanoparticles
Investigation of the static and dynamic magnetic properties of CoFe2O4 nanoparticles
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DOI：
10.1016/j.jmmm.2008.02.065
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发表时间：
2008-07
影响因子：
2.7
通讯作者：
J. L. López;H. Pfannes;R. Paniago;J. Sinnecker;M. Novak
中科院分区：
文献类型：
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作者：
J. L. López;H. Pfannes;R. Paniago;J. Sinnecker;M. Novak
我们研究了平均直径为7.2 nm的钴铁氧体纳米粒子的磁性行为。测量了胶体钴铁氧体纳米粒子在2~300K温度范围内的交流磁化率，在f=10~10,000 Hz频率范围内，零直流电场下测量了其交流磁化率。在χ‘和χ中都出现了一个明显的峰，它“是T的函数”。χ的峰温度T2与f有关，遵循伏格尔-富勒定律。这些粒子在室温下表现出超顺磁性行为，分别在∼94K和交流磁化率119K处转变为阻挡态，这与外加磁场有关。在4.2K下测得的饱和磁化强度为27.3emu/g，矫顽力为14.7kOe。通过对295K下的磁化曲线进行拟合，得到了颗粒尺寸分布，并假定颗粒尺寸分布为对数正态分布。发现粒子间相互作用影响势垒，从而使估算的磁各向异性增强，K=6×10~6erg/cm~3。在较高温度下获得的穆斯堡尔谱表明，典型的超顺磁性弛豫的磁性超精细分裂逐渐崩溃。在4.2K，穆斯堡尔谱由两个内场分别为490、470和515kOe的磁子谱拟合，分别对应于A位和B位的Fe3+离子。
We have investigated the magnetic behavior of cobalt ferrite nanoparticles with a mean diameter of 7.2nm. AC susceptibility of colloidal cobalt ferrite nanoparticles was measured as a function of temperature T from 2 to 300K under zero external DC field for frequencies ranging from f=10 to 10,000Hz. A prominent peak appears in both χ′ and χ″ as a function of T. The peak temperature T2of χ″ depends on f following the Vogel–Fulcher law. The particles show superparamagnetic behavior at room temperature, with transition to a blocked state at TBm∼94K in ZFC and 119K in AC susceptibility measurements, respectively, which depends on the applied field. The saturation magnetization and the coercivity measured at 4.2K are 27.3emu/g and 14.7kOe, respectively. The particle size distribution was determined by fitting a magnetization curve obtained at 295K assuming a log-normal size distribution. The interparticle interactions are found to influence the energy barriers yielding an enhancement of the estimated magnetic anisotropy, K=6×106erg/cm3. Mössbauer spectra obtained at higher temperatures show a gradual collapse of the magnetic hyperfine splitting typical for superparamagnetic relaxation. At 4.2K, the Mössbauer spectrum was fitted with two magnetic subspectra with internal fields Hintof 490, 470 and 515kOe, corresponding to Fe3+ions in A and B sites.