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|Type:||Artigo de periódico|
|Title:||Magnetoresistivity As A Probe To The Field-induced Change Of Magnetic Entropy In R Al2 Compounds (r=pr,nd,tb,dy,ho,er)|
|Abstract:||The heat capacity CP (T) of the ferromagnetic compounds R Al2 (R=Pr,Nd,Tb,Dy,Ho,Er) was measured at zero and applied magnetic field of 5 T in the temperature interval from 2 to 200 K. From these results are calculated the magnetic component of the entropy change, -Δ Smag (T) =S (0,T) -S (H,T). From resistivity measurements, ρ (H,T), from 2 to 300 K in the same compounds, we calculated the resistivity change due to the applied magnetic field, -Δ ρmag (T) = [ρmag (0,T) - ρmag (H,T)]. The results are compared and we observed a similar dependence between -Δ ρmag (T) and (T/ TC) m Δ Smag (T) with m=0 for T≥ TC and m=1 for T≤ TC. A simple model using a Hamiltonian considering molecular and crystalline electric fields, in a mean field approximation, is adopted for the calculus. Our results show that theory and experiment are in good agreement showing that the magnetoresistivity is a probe to the field-induced change of magnetic entropy in these compounds and can be extended to other materials. A model for the factor connecting both quantities, -Δ Smag (T) and -Δ ρmag (T), is developed. This factor contains mainly the effective exchange integral which is related to Fermi energy that in turn is related to the electron effective mass. © 2006 The American Physical Society.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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