The Magnetic Behavior of Nanocrystalline Nickel Ferrites: The Effect of Surface Roughness and Aspect Ratio on Anisotropy

摘要

Magnetic properties of nanometer-sized particles of both ferrimagnetic and ferromagnetic materials have attracted considerable attention in recent years. Some of the application areas being explored are in high-density magnetic recording media, as ferrofluids, and giant magnetoresistive systems as sensors. The paper describes the effect of surface roughness and aspect ratio on the magnetic behavior of nanocrystalline nickel ferrites. Two different kinds of measurements were performed using SQUID magnetometer: (a) zero-field cooling (ZFC) and field cooling (FC) magnetization versus temperature and (b) magnetization as a function of the applied field. The analysis of magnetic measurements indicate that while the superparamagnetic behavior is retained by the nanocrystalline ferrites of different surface roughness (8-18 A) at 300 K, the hysteresis loop at 2 K becomes non-squared and the coercivity increases with increase in surface roughness. This behavior is discussed in terms of broken bonds and degree of surface spin disorder. Changes in magnetization curve because of aspect ratio are also mentioned.