Superparamagnetic Ferrite Nanoparticles Research Articles

Detection of fine magnetic particles coated on a thread using an HTS–SQUID

Polymer-coated magnetic particles, which contain superparamagnetic ferrite nanoparticles, were attached to a nylon thread of 0.35 mm in diameter and were detected by an HTS–SQUID. The length of the sample attached into the thread was within 3 mm and its interval was 30 mm. The particles were magnetized by a coil applied dc field or by a magnet of 1.4 T. The thread ran 2 mm under the SQUID with 20–100 mm/s of the rate. Signals of magnetic beads were detected and the peak-to-peak amplitude of the signals was directly proportional to the applied field and the weight of the magnetic particles. Obtained peak-to-peak amplitude for 20 ng of magnetite particles was 350 pT at 0.25 mT of applied dc field with noise of 18 pT, and estimated detection limit was 10 ng. S/ N ratio was improved by the remanence measurement using the magnet and 5.8 ng of detection limit was obtained. This measurement has been proved to be promising for the continuous analysis of ultra dilute DNA solution.

Synthesis of Superparamagnetic Magnesium Ferrite Nanoparticles by Microwave-Hydrothermal Method

AbstractSuperparamagnetic magnesium ferrite, MgFe2O4, nanoparticles were synthesized under mild microwave hydrothermal (MH) conditions. Transmission electron microscopic studies showed that the average particle size of the ferrite obtained is ∼3 nm, with a narrow size distribution. Temperature dependent AC magnetic susceptibility measurements at 2 Oe showed characteristic feature of superparamagnetism with blocking temperature, TB, at 47 K. TB decreases with increasing DC magnetic field as evidenced by zero-field-cooled susceptibility studies at 50 and 500 Oe (TB = 38 and 27 K respectively). As a typical superparamagnetic behavior, the zero-field- cooled and the field-cooled magnetizations diverge below TB. Magnetic hysteresis behavior is observed below TB, with a high coercivity of 185 Oe at 12 K, and magnetic hysteresis behavior disappears when measured above TB. The results indicate that MH method is highly suitable for the synthesis of superparamagnetic ferrite nanoparticles of uniform size distribution.