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D. Serantes D. Baldomir M. Pereiro J.E. Arias C. Mateo-Mateo M.C. Buján-Núñez C. Vázquez-Vázquez J. Rivas 《Journal of Non》2008,354(47-51):5224-5226
We have studied the influence of the applied magnetic field on the blocking temperature (TB) of a fine magnetic particle system. By means of a Monte Carlo technique we have simulated zero field cooling (ZFC) curves under different applied fields, obtaining the respective TB as a function of H. We have focused our study on the limit H → HK (where HK is the anisotropy field), since the results found in the literature usually lack a detailed study of this range. The simulations were done at different sample concentration of the nanoparticles, with the purpose of observing how the magnetic dipolar interaction affects the field dependence of TB. The classical expression predicts TB to disappear for H ? HK, independently of the dipolar interaction strength. Our simulations show that at strong interacting conditions TB exists even for fields H > HK. 相似文献
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C. Mateo-Mateo C. Vázquez-Vázquez M.C. Buján-Núñez M.A. López-Quintela D. Serantes D. Baldomir J. Rivas 《Journal of Non》2008,354(47-51):5236-5237
Cobalt ferrite–poly(N-vinyl-2-pyrrolidone) nanocomposites were prepared by drying a dispersion of cobalt ferrite (CoFe2O4) nanoparticles and poly(N-vinyl-2-pyrrolidone). Magnetic measurements indicate a superparamagnetic behavior. Zero-field-cooling magnetization experiments at 100 Oe show different trends depending on the CoFe2O4 nanoparticles size. For the smaller ones (3.9 nm), the blocking temperatures shift to lower temperatures with increasing concentration; however, this shift is not observed for the larger ones (6.6 nm). These differences can be related to the anisotropy constant of the CoFe2O4 nanoparticles and the interparticle dipolar interactions. 相似文献
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Magnetocaloric properties of as-quenched Ni50.4Mn34.9In14.7 ferromagnetic shape memory alloy ribbons
Sánchez Llamazares J. L. García C. Hernando B. Prida V. M. Baldomir D. Serantes D. González J. 《Applied Physics A: Materials Science & Processing》2011,103(4):1125-1130
The temperature dependences of magnetic entropy change and refrigerant capacity have been calculated for a maximum field change
of Δ
H=30 kOe in as-quenched ribbons of the ferromagnetic shape memory alloy Ni50.4Mn34.9In14.7 around the structural reverse martensitic transformation and magnetic transition of austenite. The ribbons crystallize into
a single-phase austenite with the L21-type crystal structure and Curie point of 284 K. At 262 K austenite starts its transformation into a 10-layered structurally
modulated monoclinic martensite. The first- and second-order character of the structural and magnetic transitions was confirmed
by the Arrott plot method. Despite the superior absolute value of the maximum magnetic entropy change obtained in the temperature
interval where the reverse martensitic transformation occurs
(|\varDelta SMmax|=7.2 J kg-1 K-1)(|\varDelta S_{\mathrm{M}}^{\max}|=7.2\mbox{ J}\,\mbox{kg}^{-1}\,\mbox{K}^{-1}) with respect to that obtained around the ferromagnetic transition of austenite
(|\varDelta SMmax|=2.6 J kg-1 K-1)(|\varDelta S_{\mathrm{M}}^{\max}|=2.6\mbox{ J}\,\mbox{kg}^{-1}\,\mbox{K}^{-1}), the large average hysteretic losses due to the effect of the magnetic field on the phase transformation as well as the narrow
thermal dependence of the magnetic entropy change make the temperature interval around the ferromagnetic transition of austenite
of a higher effective refrigerant capacity (RCmagneff=95J kg-1\mathrm{RC}^{\mathrm{magn}}_{\mathrm{eff}}=95\mbox{J}\,\mbox{kg}^{-1} versus RCstructeff=60J kg-1)\mathrm{RC}^{\mathrm{struct}}_{\mathrm{eff}}=60\mbox{J}\,\mbox{kg}^{-1}). 相似文献
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M.C. Buján-Núñez N. Fontaiña-Troitiño C. Vázquez-Vázquez M.A. López-Quintela Y. Piñeiro D. Serantes D. Baldomir J. Rivas 《Journal of Non》2008,354(47-51):5222-5223
Zero field cooling curves (ZFC) under a relatively big magnetic field have been simulated in order to study the influence of the nanoparticle concentration on the rate of increase of the blocking temperature and its dependence with the nanoparticle size. Results show that for all nanoparticle concentrations the blocking temperature increases linearly with the nanoparticle size. The rate of increase of the blocking temperature is larger for larger nanoparticle concentrations, although it tends to a constant value for very large interactions between particles. 相似文献
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