Magnetic behavior of zero-field-frozen ferrofluid

In contrast to the spin glass-like state described in the literature, an al ternative approach to explain the temperature dependence of the magnetizati on in a zero-field-frozen ferrofluid (ZFFF) is proposed in this work. It is claimed that the presence of a well-defined peak in the magnetization (M) versus temperature (T) curve results from the following combined effects: t he temperature dependence of the reorientation of the magnetic moment assoc iated to the nanomagnetic particle, saturation magnetization and magnetic a nisotropy, The sample used in this work is a Nickel ferrite-based ferroflui d, which was investigated using magnetometry and transmission electron micr oscopy, the latter indicating the presence of nanomagnetics with a mean par ticle diameter of 11.1 nm and standard deviation of 0.37. Excellent agreeme nt between theory and experiment is found for the M vs T curve using the fe rrofluid sample containing 3 x 10(16) particle/cm(3) and submitted to magne tic fields of 1, 3 and 5 kG. (C) 2000 Elsevier Science Ltd. All rights rese rved.