表面活性剂介导的Ca-Mg掺杂的纳米铁水化物的穆斯堡尔谱和磁学研究
Mössbauer and Magnetic Studies of Surfactant Mediated Ca-Mg Doped Ferrihydrite Nanoparticles
摘要：
采用表面活性剂共沉淀法合成了超细（2-5 nm）的无定形钙镁共掺杂水铁矿。通过Ca-Mg共掺杂的无定形水铁矿的演变与我们早期对单独的Ca和Mg掺杂研究的调查完全不同。通过X射线衍射（XRD）和穆斯堡尔谱（Mössbauer spectroscopy）在室温和低温（40 K和20 K）下证实了本研究中的水铁矿为非晶相。在空气气氛中，分别在400、600和800 $^0$ C下退火，得到了晶粒尺寸分别为8、38和70 nm的纳米赤铁矿颗粒。超顺磁性已被发现在8 nm大小的赤铁矿纳米粒子，这已被证实从磁滞回线与零剩磁和矫顽场，也从超顺磁性的穆斯堡尔谱的室温双峰。通过室温磁滞回线测量和穆斯堡尔谱学研究了38和70 nm尺寸的颗粒的磁性。这些赤铁矿纳米颗粒中的矫顽场随着颗粒尺寸的增加而增加。在800 $^0$ C退火样品中检测到少量的尖晶石MgFe $_{2}$ O $_{4}$相。
英文摘要：
Ultrafine (2-5 nm) particles of amorphous Ca-Mg co-doped ferrihydrite have been synthesized by surfactant mediated co-precipitation method. The evolution of the amorphous ferrihydrite by Ca-Mg co-doping is quite different from our earlier investigations on individual Ca and Mg doping studies. Amorphous phase of ferrihydrite for the present study has been confirmed by X-ray diffraction (XRD) and Mössbauer spectroscopy at room temperature and low temperatures (40 K and 20 K). Hematite nanoparticles with crystallite size about 8, 38 and 70 nm were obtained after annealing the as-prepared samples at 400, 600 and 800$^0$C respectively in air atmosphere. Superparamagnetism has been found in 8 nm sized hematite nanoparticles which has been confirmed from the magnetic hysteresis loop with zero remanent magnetization and coercive field and also from the superparamagnetic doublet of its room temperature Mössbauer spectrum. The magnetic properties of the 38 and 70 nm sized particles have been studied by room temperature magnetic hysteresis loop measurements and Mössbauer spectroscopy. The coercive field in these hematite nanoparticles increases with increasing particle size. Small amount of spinel MgFe$_{2}$O$_{4}$ phase has been detected in the 800$^0$C annealed sample.
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