Interparticle interaction effects in the magnetic properties of NiO nanorods

Magnetic properties of nanorods of NiO (diameter ≈ 5 nm and average aspect ratio ≈ 12 ), with and without oleic acid coating, are reported. Temperature variations (5 to 300 K) of the magnetization and electron magnetic resonance (EMR) spectra were measured to determine the respective blocking temperatures T b ( m ) and T b ( EMR ) . The following differences are noted: (1) T b ( m ) is reduced from 230 K (uncoated) to 85 K (coated) for H = 25 Oe ( 2.5 mT ) ; (2) Decrease of T b ( m ) with H is weaker and the ratio T b ( EMR ) ∕ T b ( m ) is smaller for the uncoated particles. These differences are due to stronger interparticle interaction present in the uncoated particles.