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首页> 外文期刊>Journal of Physics. Condensed Matter >Size-dependent magnetic properties of VO2 nanocrystals dispersed in a silica matrix
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Size-dependent magnetic properties of VO2 nanocrystals dispersed in a silica matrix

机译：分散在二氧化硅基质中的VO2纳米晶体的尺寸依赖性磁性

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Magnetic nanocrystalline VO2 particles have been successfully synthesized in a silica glass matrix by the sol-gel method at calcination temperatures of 700 degrees C and above. The presence of small quantities of diamagnetic V2O5 nanocrystals in glass samples calcined at >= 800. C has been confirmed. The thermal behavior of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of VO2 nanocrystals in the 10-300 K temperature interval have demonstrated that the VO2 nanocrystals present in these glasses display superparamagnetic-ferromagnetic transition at low temperatures. X-band electron paramagnetic resonance (EPR) spectra of VO2 nanoparticles have depicted broad symmetric lines [Delta H-pp similar to 104 mT at room temperature (RT) and 250 mT at liquid nitrogen temperature (LNT)]. The increase in EPR line intensity on going from RT to LNT suggests that VO2 nanocrystals have undergone ferromagnetic-like ordering in the temperature interval RT-77 K. The presence of small numbers of isolated VO2+ ions in the SiO2 matrix has also been confirmed from EPR studies. From EPR and optical spectral studies it has been shown that the VO2+ ion has square pyramidal conformation with tetragonal compression having C-4v symmetry. It is established that the in-plane sigma bonding and out-of-plane pi bonding are predominantly ionic in nature.
机译：磁性纳米晶体VO2粒子已通过溶胶-凝胶法在700摄氏度及以上的煅烧温度下成功合成在二氧化硅玻璃基质中。已确认在> = 800.C的煅烧玻璃样品中存在少量的反磁性V2O5纳米晶体。 VO2纳米晶体在10-300 K温度区间内的磁化（零场冷却和场冷却）和磁滞的热行为表明，这些玻璃中的VO2纳米晶体在低温下显示出超顺磁-铁磁跃迁。 VO2纳米粒子的X带电子顺磁共振（EPR）光谱描绘了宽对称线[在室温（RT）类似于104 mT在液氮温度（LNT）类似于250 mT的ΔH-pp]。从RT到LNT时EPR线强度的增加表明VO2纳米晶体在RT-77 K的温度区间内经历了类似铁磁的有序化。从EPR中也证实了SiO2基质中存在少量孤立的VO2 +离子学习。从EPR和光谱研究中已经表明，VO 2+离子具有正方形金字塔构象，具有C-4v对称性的四方压缩。已经确定，面内σ键和面外π键本质上主要是离子性的。

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