磁场中磁液微粒超顺磁性稳定混悬的临界尺寸

Critical Size of Particles in Superparamagnetic Magnetic Agents Keeping Stable and Superparamagnetism in Magnetic Fields

探讨处于磁场中超顺磁性混悬液(SMA)中磁性微粒既能保持稳定混悬、又具有超顺磁性的临界尺寸.根据超顺磁性理论,推导有无外加磁场时微粒显示超顺磁性的理论公式.根据磁学理论,分析SMA的稳定机理;推导外加磁场中SMA稳定悬浮的临界尺寸公式.由相应的理论公式可知,无外磁场时Fe3O4和Fe2O3微粒显示超顺磁现象的临界尺寸理论值分别为25.0 nm和31.8 nm,有外磁场时,临界尺寸下降,且随磁场的增强而下降.同时磁粒稳定混悬的临界尺寸也会随梯度磁场的增强而下降.若要既能稳定悬浮又具有超顺磁性,其临界尺寸应选两者中的最小值.

Explores the critical size of particles in superparamagnetic magnetic agent （SMA） keeping stable and superparamagnetism in magnetic fields. Based on superparamagnetic theory, the expression for keeping superparamagnetism is deduced. Based on magnetic theory, the mechanism of stability of contrast agent is analyzed, and the critical size of magnetic microparticles keeping stable in the contrast agent developed. The critical size of Fe3O4 and Fe2O3 particals keeping superparamagnetism is 25.0 nm or 31.5 nm respectively. The size decreases as the magnetic fields grow up. Meanwhile the size of microparticles decreases as the gradient magnetic fields grow up. The definite size to be chosen is the lesser one between them.