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. Co83Ir17 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.