Surface Spin Disorder in Fe $_{3}$ O $_{4}$ Nanoparticles Probed by Electron Magnetic Resonance Spectr

SQUID magnetometry and electron magnetic resonance (EMR) spectroscopy at 9.28 GHz were employed to probe magnetism and surface spin disorder in Fe₃O₄ nanoparticles. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis showed magnetite particles with size sime8 nm. Magnetization (M) versus temperature studies yielded blocking temperature T_Bsime 170 K in H= 50 Oe. For T>T_B, M scales approximately as H/T with mu_psime5400 mu_B as the magnetic moment/particle. At 5 K, the magnitudes of hysteresis loop parameters viz. coercivity H_c sime 37 Oe and saturation magnetization M_s= 62 emu/g are considerably smaller than the reported values for larger 150 nm Fe₃O₄ particles. In EMR studies, a single symmetric line at gsime2.11 with linewidth DeltaH= 850Oe is observed at 300 K with the g-value and DeltaH increasing with decreasing T. These results are interpreted in terms of a disordered surface spin layer of 0.5 nm thickness