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, DeltaE, 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