Bulk cobalt ferrite, being a hard ferrite, shows high magnetization, high resistivity and high coercivity. If thin films of cobalt ferrite can be deposited at a low enough temperature and if its coercivity can be reduced, cobalt ferrite will make a very good candidate for use as a magnetic core of an integrated inductor in RF-CMOS ICs. Though polycrystalline and epitaxial thin films of cobalt ferrite have been made by various techniques, there are no reports of thin films of superparamagnetic cobalt ferrite. In this work, nanocrystalline cobalt ferrite thin films, which are superparamagnetic as deposited, have been prepared in the solution medium at ∼190 °C, using microwave irradiation. The as-prepared films have a saturation magnetization (MS) of 401 emu/cc and coercivity (HC) of 19 Oe at room temperature for a crystallite size of 2 nm. The cobalt ferrite powder obtained as a by-product during the same process has MS of 50 emu/g and HC of 5 Oe at room temperature, making it superparamagnetic. The as-prepared films were annealed in air at 300 °C for 5 min and 10 min. Annealing for 10 min results in an increase in crystallite size to 36 nm, MS increases from 401 emu/cc to 545 emu/cc, and HC increases from 19 Oe to 860 Oe. The change in magnetic properties can be directly associated with change in the crystallite size and degree of crystallographic inversion, as determined by neutron diffraction and deduced from X-ray photoelectron spectroscopy.

中文翻译：

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低温下沉积的超顺磁性纳米晶钴铁氧体薄膜的磁性能

摘要 块状钴铁氧体是一种较硬的铁氧体，具有高磁化、高电阻和高矫顽力。如果可以在足够低的温度下沉积钴铁氧体薄膜，并且可以降低其矫顽力，那么铁氧体钴将非常适合用作 RF-CMOS IC 中集成电感器的磁芯。尽管已经通过各种技术制备了钴铁氧体的多晶和外延薄膜，但还没有关于超顺磁性钴铁氧体薄膜的报道。在这项工作中，使用微波辐射在约 190 °C 的溶液介质中制备了沉积时具有超顺磁性的纳米晶钴铁氧体薄膜。对于 2 nm 的微晶尺寸，所制备的薄膜在室温下具有 401 emu/cc 的饱和磁化强度 (MS) 和 19 Oe 的矫顽力 (HC)。在同一过程中作为副产品获得的钴铁氧体粉末在室温下具有 50 emu/g 的 MS 和 5 Oe 的 HC，使其具有超顺磁性。所制备的薄膜在空气中在 300°C 下退火 5 分钟和 10 分钟。退火 10 分钟导致微晶尺寸增加到 36 nm，MS 从 401 emu/cc 增加到 545 emu/cc，HC 从 19 Oe 增加到 860 Oe。磁性的变化可以与微晶尺寸和晶体学反转程度的变化直接相关，如通过中子衍射确定并从 X 射线光电子能谱推断。退火 10 分钟导致微晶尺寸增加到 36 nm，MS 从 401 emu/cc 增加到 545 emu/cc，HC 从 19 Oe 增加到 860 Oe。磁性的变化可以与微晶尺寸和晶体学反转程度的变化直接相关，如通过中子衍射确定并从 X 射线光电子能谱推断。退火 10 分钟导致微晶尺寸增加到 36 nm，MS 从 401 emu/cc 增加到 545 emu/cc，HC 从 19 Oe 增加到 860 Oe。磁性的变化可以与微晶尺寸和晶体学反转程度的变化直接相关，如通过中子衍射确定并从 X 射线光电子能谱推断。