Magnetization Process of h.c.p.-CoIr Nanoparticles With Negative Uniaxial Magnetocrystalline Anisotropy

To increase the superparamagnetic blocking frequency, we propose magnetic nanoparticles with negative uniaxial magnetocrystalline anisotropy,
$K_u^ grain$
. Using this material, both high ferromagnetic resonance frequency,
$f_ r$
, and low magnetic potential height,
$Delta E$
, can be satisfied simultaneously. Thus,
$f_ b$
can be greatly improved. From the results of DC magnetization process of highly oriented h.c.p. Co
$_83$
Ir
$_17$
nanogranular with negative
$K_ u^ grain$
, it is verified that the nanoparticles with negative
$K_ u^ grain$
have superparamagnetic properties only in the c-plane.