Abstract
Zero-field cooled (ZFC) and field cooled (FC) magnetizations are measured for NiO nanoparticles of size 5–55 nm. Variations with particle size (
d
) and temperature of the coercivity (
H
C
), exchange bias field (
H
E
), coercivity enhancement (
Δ
H
C
) are discussed. The results are interpreted in terms of exchange bias (EB) models.
H
E
and the ferromagnetic magnetization (
M
FM
) arising from uncompensated surface spins of otherwise antiferromagnetic (AF) NiO show inverse trends when presented as functions of particle size. An interfacial exchange energy
Δ
σ
of ∼0.03 erg/cm
2, comparable to those of NiO/Co and NiO/permalloy bilayers, is observed. Finally, it has been found that the coercivity enhancement
Δ
H
C
=
H
C
(
FC
)
−
H
C
(
ZFC
)
scales with the interfacial exchange energy in the present system.