Orientation of the magnetization easy axes of interacting nanoparticles: Influence on the hyperthermia properties

• Heating is strongly influenced by easy-axes collinearity and field direction.
• Easy-axes collinearity marks a threshold for heat dissipation at low interaction.
• Increasing interactions attenuates this influence.

The relative orientation between anisotropy easy axes of magnetization of magnetic nanoparticles (MNPs) and the applied magnetic field direction determines their heating properties and thus needs to be considered for accurate heating applications. In this work we systematically study the heating properties of a system of interacting MNPs with ferromagnetic-like behavior (i.e. in the blocked state), randomly distributed in space, as a function of the degree of collinearity of their easy anisotropy axes along the magnetic field direction. The easy-axes of the particles were distributed at random within cones of different aperture angles (0, 10, 22.5 and 45 degrees with respect to the field direction), under different conditions of magnetic field amplitude and interparticle interactions. Our results show that easy-axes collinearity marks a clear threshold for heat dissipation at low interacting conditions, but increasing interactions tends to attenuate this effect.