Surface anisotropy and surface/core interaction in Co-Ni-B and Fe-Ni-B dispersed amorphous nanoparticles

DE BIASI EMILIO; RAMOS CARLOS; ZYSLER ROBERTO; ROMERO HÉCTOR

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

Año: 2005 vol. 71 p. 1 - 6

0163-1829

We report on Monte Carlo simulations of the magnetization behavior of ,3 nm of sFe0.26Ni0.74d50B50 and,3 nm of sFe0.26Ni0.74d50B50 and sCo0.25Ni0.75d65B35 ferromagnetic amorphous nanoparticles dispersed in a polymer matrix. Simulations based on a core-shell model, describing the nanoparticles as consisting of a ferromagnetically ordered core and a disordered surface shell, reproduce satisfactorily the significant features observed in hysteresis cycles, i.e.,Co0.25Ni0.75d65B35 ferromagnetic amorphous nanoparticles dispersed in a polymer matrix. Simulations based on a core-shell model, describing the nanoparticles as consisting of a ferromagnetically ordered core and a disordered surface shell, reproduce satisfactorily the significant features observed in hysteresis cycles, i.e., HcsTd and MrsTd curves. The results provide clear evidence of the major role played at low temperature by surface anisotropy and surface-core exchange interaction in determining some anomalies of the hysteresis cycles and the large increase in effective particle anisotropy at low temperature.csTd and MrsTd curves. The results provide clear evidence of the major role played at low temperature by surface anisotropy and surface-core exchange interaction in determining some anomalies of the hysteresis cycles and the large increase in effective particle anisotropy at low temperature.