A novel technique was used for the synthesis of manganese oxide nanocrystal by applying an external magnetic field (EMF) on the precursor solution before sonication with ultrasonic bath. The results were compared in the presence and absence of EMF. Manganese acetate solution as precursor was circulated by a pump at constant speed (7 rpm, equal to flow rate of 51.5 mL/min) in an EMF with intensity of 0.38 T in two exposure times (tMF, 2 h and 24 h). Then, the magnetized solution was irradiated indirectly by ultrasonic bath in basic andneutralmedia.Oneexperimentwasdesignedfortheeffectofoxygenatmosphereinthecaseofmagnetic treated solution in neutral medium. The as prepared samples were characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (HRTEM, TEM), energy-dispersive spectrum (EDS), and superconducting quantum interference device (SQUID) analysis. In neutral medium, the sonication of magnetized solution (tMF, 24 h) led mainly to a mixture of Mn3O4 (hausmannite) and c-MnOOH (manganite) and sonication of unmagnetized solution led to a pure Mn3O4. In point of particle size, the larger and smaller size of nanoparticles was obtained with and without magnetic treatment, respectively. In addition, the EMF was retarded the nucleation process, accelerated the growth of the crystal, and increased the amount of rod-like structure especially in oxygen atmosphere. In basic medium, a differencewas observed onthe compositionofthe products between magnetictreated and untreated solution.Forthesesamples,themagneticmeasurementsasafunctionoftemperaturewereexhibitedareduction in ferrimagnetic temperature to Tc = 39 K, and 40 K with and without magnetic treatment, respectively. The ferrimagnetic temperature was reported for the bulk at Tc = 43 K. A superparamagnetic behavior was observed at room temperature without any saturation magnetization and hysteresis in the measured field strength.TheeffectofEMFonthesamplepreparedinthebasicmediumwasnegligiblebut,inthecaseofneutralmedium,theEMFaffectedtheslopeofthemagnetizationcurves.Themagnetizationatroomtemperature washigherforthesamplesobtainedinneutralmediumwithoutmagnetictreatment.Inaddition,ahorizontal shift loop was observed in neutral medium at low temperature.
کلید واژگان :Hausmannite Manganite External magnetic field Superparamagnetic Ferrimagnetic
ارزش ریالی : 600000 ریال
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