Magnetic irreversibility and saturation criteria in ultrasmall bi-magnetic nanoparticles

A numerical study on the interplay between the intra-particle and interparticle characteristics in bimagnetic soft/soft and hard/soft ultrasmall nanoparticle assemblies

“…Long-range inter-particle dipolar interactions among all spins in the assemblies are considered. In the case of the dense assembly (powder sample) for the particles that are in contact, because of the very small shell thickness, 31 the particle core spin interacts with the nearest neighbor shell spins via exchange interactions (J csh1 , J csh2 ). 37 The shell spins of the nearest neighbours are also exchange coupled (J sh1sh2 ).…”

“…22,[27][28][29] Indeed, in previous experimental studies, we have investigated the effect of core and shell composition on the exchange bias properties of MnFe 2 O 4 @g-Fe 2 O 3 and CoFe 2 O 4 @g-Fe 2 O 3 core/shell NPs of size $ 3 nm at low temperature (a few Ks). 24,[30][31][32] By studying dilute and dense dispersions as well as powders, it has been demonstrated experimentally that inter and intraparticle interactions play an important role in the EB properties. Our nding showed that in concentrated frozen dispersions, the dipolar interparticle interaction reduced the exchange bias eld.…”

“…In all cases we discuss the numerical results in the context of our experimental ndings. 24,30,31,35,36 O 3 shell thickness t sh ¼ 0.5 nm) assemblies in frozen fer-rouids (very dilute samples) and powders (dense samples), we consider systems of N ultra-small spherical nanoparticles with a ferrimagnetic (FiM) core/FiM shell morphology. We perform the Monte Carlo simulations technique with the implementation of the Metropolis algorithm to calculate the magnetic behaviour of these assemblies at low temperature T ¼ 0.01 in our units which corresponds to 5 K.…”

Magnetic Properties of Bi-Magnetic Core/Shell Nanoparticles: The Case of Thin Shells

“…Indeed, the cobalt ions with the high anisotropy are found to have been less subjected to the canting, while in softer ferrites the spin canting may be stronger [32,33]. According to the literature, the surface and interface terms contribute to the uniaxial magnetic anisotropy of magnetic NPs [34][35][36]. In this case, the surface/interface effects in both core/shell systems demonstrated a tendency towards cubic anisotropy with M R /M S value of around 0.75, which is close to the theoretical value of ~0.8, while in the case of the uniaxial anisotropy, the lower value of ~0.5 is expected [20].…”

“…Indeed, the cobalt ions with the high anisotropy are found to have been less subjected to the canting, while in softer ferrites the spin canting may be stronger[32,33]. According to the literature, the surface and interface terms contribute to the uniaxial magnetic anisotropy of magnetic NPs[34][35][36]. In this case, the surface/interface effects in both core/shell systems demonstrated a tendency towards cubic anisotropy with M R /M S value of around 0.75, which is close to the theoretical value of ~0.8, while in the case of the uniaxial anisotropy, the lower value of ~0.5 is expected[20].A typical fingerprint of exchange-coupled AFM/F(i)M systems with the Néel temperature (T N ) of an AFM phase below that of the Curie (Néel) temperature (T C ) of an F(i)M phase is the horizontal shift of the hysteresis cycle (i.e., Exchange Bias) that may be observed under specific conditions[37,38].…”