Size effects in the magnetic anisotropy of embedded cobalt nanoparticles: from shape to surface

Abstract

Strong size-dependent variations of the magnetic anisotropy of embedded cobalt clusters are evidenced quantitatively by combining magnetic experiments and advanced data treatment. The obtained values are discussed in the frame of two theoretical models that demonstrate the decisive role of the shape in larger nanoparticles and the predominant role of the surface anisotropy in clusters below 3 nm diameter.

Impact of aligned carbon nanotubes array on the magnetostatic isolation of closely packed ferromagnetic nanoparticles

“…We will neglect this last term further in this study. The effective anisotropy constant K found above, determines the total contribution of all components [60,61].…”

Size effects of the magnetic anisotropy of fcc cobalt nanoparticles embedded in copper

“…These comprise, amongst others, size effects, where, on the one hand, the reduced dimensionality can induce new crystalline phases such as fivefold symmetric icosahedral structures [1] and, on the other hand, the electronic confinement can lead to effects such as the localized surface plasmon resonance [2] or superparamagnetism [3]. We have demonstrated in a recent publication [4] that the advanced treatment of magnetic data from cobalt clusters embedded in copper matrices allows the highly accurate characterization and determination of properties such as the magnetic particle diameter distribution as well as the effective magnetic anisotropy constant, its dispersion about a mean value and a possible biaxial component. We have quantified size-dependent variations in the effective magnetic anisotropy constant of a factor of two in the range between 1.9 and 5.5 nm.…”

Electronic Transport and Magnetic Properties of Co/SiO2Magnetic Nanocomposites

“…This is because the effective magnetic energy barrier of nanoparticles results from various contributions, namely, cubic magnetocrystalline, surface, shape and magnetoelastic anisotropy. Recent results indicate, that for Co nanoparticles with D < 3 nm the surface anisotropy is dominating, whereas for larger nanoparticles ( D > 3 nm) the shape anisotropy is decisive . It has been also found experimentally that for nearly spherical 20 nm fcc‐Co nanoparticles the presence of planar defects, such as twin boundaries and stacking faults, alter the magnetocrystalline anisotropy leading to dominating shape anisotropy that should be of the order of 10 5 erg/cm 3 (10 4 J m −3 ) .…”