Microwave synthesis and magnetic properties of amorphous ferrites

非晶铁氧体的微波合成及磁性能

• 批准号: 12450263
• 负责人: TAKIZAWA Hirotsugu
• 金额: $ 6.34万
• 依托单位: Tohoku University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450263/
• 关键词: microwave heating; ferrites; amorphous; spinel-type oxides; ferromagnetism; electro-magnetic processing; millimeter-wave; 積層欠陥; アルモファス; 拡散; ビクスバイト型酸化物; ガーネット型酸化物; 結晶化

Various amorphous ferrites were synthesized by microwave irradiation on the powder mixture of component oxides using 28 GHz frequency. Microwave absorbing behavior of component oxides was analyzed by measuring the temperature-time profiles under microwave irradiation. Strong microwave absorption was observed in powder mixture of oxides with spinel-and magnetoplumbite-type compositions. After irradiation of high power microwaves, the specimens turned to amorphous phases showing ferromagnetism. These amorphous phases did not crystallize by high-temperature annealing at 1200℃, but easily crystallized by applying shear stress. It was found that the tendency of amorphisation strongly correlate with the magnetostriction constant of the crystalline ferrites. The obtained amorphous ferrites shows ferromagnetic behavior similar to those of crystalline phases with the same compositions, i.e., the Curie temperature and saturation magnetization are nearly the same for both amorphous and crystalline phases, but the coercive force (Hc) of the amorphous phase is much smaller than that of crystalline phase. In the case of ZnFe_2O_4, the amorphous phase shows ferromagnetism although the crystalline ZnFe_2O_4 (normal spinel-type) is antiferromagnetic. The possible presence of tetrahedral Fe^<3+> ion confirmed by XPS spectra. The mechanism of amorphisation is discussed in terms of material-microwave interactions, especially, structure fluctuation induced by coupling with microwave energy.

采用微波辐射技术，在28 GHz的频率下，合成了多种非晶铁氧体。通过测量微波辐射下的温度-时间曲线，分析了复合氧化物的微波吸收行为。在尖晶石型和磁铅石型氧化物的粉末混合物中观察到强微波吸收。在高功率微波辐照后，样品变成非晶相，显示铁磁性。这些非晶相在1200℃高温退火时不晶化，而在剪切应力作用下易晶化。结果发现，非晶化的趋势强烈相关的磁致伸缩常数的结晶铁氧体。所获得的非晶铁氧体显示出与具有相同组成的晶相的铁磁行为相似的铁磁行为，即，非晶相和晶相的居里温度和饱和磁化强度几乎相同，但非晶相的矫顽力（Hc）远小于晶相。在ZnFe_2O_4的情况下，非晶相显示铁磁性，而晶态ZnFe_2O_4（正常尖晶石型）显示反铁磁性。XPS谱图证实了四面体Fe^<3+>离子的可能存在。从材料与微波相互作用的角度，特别是与微波能量耦合引起的结构涨落，讨论了非晶化的机理。