High magnetization and the high-temperature superparamagnetic transition with intercluster interaction in disordered zinc ferrite thin film
High magnetization and the high-temperature superparamagnetic transition with intercluster interaction in disordered zinc ferrite thin film
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DOI：
10.1088/0953-8984/17/1/013
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发表时间：
2005-01
期刊：
影响因子：
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通讯作者：
S. Nakashima;K. Fujita;Katsuhisa Tanaka;K. Hirao
中科院分区：
文献类型：
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作者：
S. Nakashima;K. Fujita;Katsuhisa Tanaka;K. Hirao
用溅射方法在玻璃衬底上沉积了接近室温的锌铁氧体薄膜，研究了其磁性。X-射线衍射仪分析表明，薄膜由纳米晶的ZnFe2O4组成，其尺寸约为10 nm。300K时的磁化强度随外加磁场的变化呈现亚铁磁性，当外加磁场大于30kOe时，磁化强度趋于饱和，达到32emu g−1的高值。认为溅射法制备的ZnFe2O4薄膜，由于需要快速冷却水蒸气而形成固相，导致了锌、铁离子在尖晶石结构中的随机分布。在这种情况下，Fe3+离子同时占据八面体和四面体位置，它们之间强烈的超交换作用导致了伴随着高磁化强度的亚铁磁性。静态和动态磁响应，如线性交流磁化率的频率依赖关系、非线性交流磁化率的温度依赖关系、零场冷却(ZFC)和场冷直流磁化强度之间的差异以及ZFC磁化强度的弛豫，表明该薄膜的磁性是由于磁团簇之间相互作用的超顺磁性所致。自旋冻结发生在高于室温(K)的温度。
Magnetic properties have been investigated for a zinc ferrite thin film deposited on glass at a substrate temperature close to room temperature using a sputtering method. X-ray diffraction analysis reveals that the thin film consists of nanocrystalline ZnFe2O4 with the size of approximately 10 nm. The magnetization at 300 K as a function of the external magnetic field shows ferrimagnetic behaviour, and tends to be saturated to the high value of 32 emu g−1 when the external magnetic field is higher than 30 kOe. It is considered that the preparation of the ZnFe2O4 thin film by the sputtering method, which involves very rapid cooling of vapour to form the solid-state phase, causes the random distribution of Zn2+ and Fe3+ ions in the spinel structure. In such a situation, Fe3+ ions occupy both octahedral and tetrahedral sites, and the strong superexchange interaction among them gives rise to ferrimagnetic properties accompanied with high magnetization. The static and dynamic magnetic responses, such as the frequency dependence of the linear ac susceptibility, the temperature dependence of the nonlinear ac susceptibility, the discrepancy between the zero-field-cooled (ZFC) and field-cooled dc magnetizations, and the relaxation of the ZFC magnetization, demonstrate that the magnetism of the present thin film is attributable to the superparamagnetism with the interaction among magnetic clusters. Spin freezing occurs at a temperature higher than room temperature ( K).