Anisotropy evolution of nanoparticles under annealing: Benefits of isothermal remanent magnetization simulation

Abstract Isothermal remanent magnetization (IRM) combined with Direct current demagnetization (DcD) are powerful tools to qualitatively study the interactions (through the Δ m parameter) between magnetic particles in a granular media. For magnetic nanoparticles diluted in a matrix, it is possible to reach a regime where Δ m is equal to zero, i.e. where interparticle interactions are negligible: one can then infer the intrinsic properties of nanoparticles through measurements on an assembly, which are analyzed by a combined fit procedure (based on the Stoner–Wohlfarth and Neel models). Here we illustrate the benefits of a quantitative analysis of IRM curves, for Co nanoparticles embedded in amorphous carbon (before and after annealing): while a large anisotropy increase may have been deduced from the other measurements, IRM curves provide an improved characterization of the nanomagnets intrinsic properties, revealing that it is in fact not the case. This shows that IRM curves, which only probe the irreversible switching of nanomagnets, are complementary to widely used low field susceptibility curves.