arXiv subjects

W. C. Nunes

Publications and source records attributed to W. C. Nunes.

3 recordsLinked to original sources

arXiv2004

Temperature dependence of the coercive field in single-domain particle systems

The magnetic properties of Cu97Co3 and Cu90Co10 granular alloys were measured over a wide temperature range (2 to 300K). The measurements show an unusual temperature dependence of the coercive field. A generalized model is proposed and explains well the experimental behavior over a wide temperature range. The coexistence of blocked and unblocked particles for a given temperature rises difficulties that are solved here by introducing a temperature dependent blocking temperature. An empirical factor gamma arise from the model and is directly related to the particle interactions. The proposed generalized model describes well the experimental results and can be applied to other single-domain particle system.

cond-mat.mtrl-sci↗

arXiv2002

The role of the alloy structure in the magnetic behavior of granular systems

The effect of grain size, easy magnetization axis and anisotropy constant distributions in the irreversible magnetic behavior of granular alloys is considered. A simulated granular alloy is used to provide a realistic grain structure for the Monte Carlo simulation of the ZFC-FC curves. The effect of annealing and external field is also studied. The simulation curves are in good agreement with the FC and ZFC magnetization curves measured on melt spun Cu-Co ribbons.

cond-mat.mtrl-sci↗

arXiv1999

Low temperature specific heat of the molecular cluster Fe$_{8}$: contribution of the local field

We present low temperature specific heat and ac-susceptibility measurements on Fe$_{8}$ powdered sample. Below 1.3 K, superparamagnetic blocking effects as well as an excess specific heat contribution are evident. The latter is attributed to a splitting of the ground state doublet in an inhomogeneous local field of hyperfine and dipolar origin. The local field contributions are evident in the resonances observed in the field dependent ac-susceptibility and specific heat below 0.5 K. The low temperature Schottky contribution allowed us to check the crystal field parameters of effective spin Hamiltonians, recently proposed to simulate EPR and inelastic neutron scattering experiments.

cond-mat.mes-hall↗