Magnetoresistivity as a probe to the field-induced change of magnetic entropy inRAl2compounds(R=Pr,Nd,Tb,Dy,Ho,Er)
| Autor: | J.C.P. Campoy, Adelino A. Coelho, E. J. R. Plaza, Sergio Gama |
|---|---|
| Rok vydání: | 2006 |
| Předmět: | |
| Zdroj: | Physical Review B. 74 |
| ISSN: | 1550-235X 1098-0121 |
| Popis: | The heat capacity ${C}_{P}(T)$ of the ferromagnetic compounds $R{\mathrm{Al}}_{2}$ $(R=\mathrm{Pr},\mathrm{Nd},\mathrm{Tb},\mathrm{Dy},\mathrm{Ho},\mathrm{Er})$ was measured at zero and applied magnetic field of $5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ in the temperature interval from $2\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. From these results are calculated the magnetic component of the entropy change, $\ensuremath{-}\ensuremath{\Delta}{S}_{\mathit{mag}}(T)=S(0,T)\ensuremath{-}S(H,T)$. From resistivity measurements, $\ensuremath{\rho}(H,T)$, from $2\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in the same compounds, we calculated the resistivity change due to the applied magnetic field, $\ensuremath{-}\ensuremath{\Delta}{\ensuremath{\rho}}_{\mathit{mag}}(T)=[{\ensuremath{\rho}}_{\mathit{mag}}(0,T)\ensuremath{-}{\ensuremath{\rho}}_{\mathit{mag}}(H,T)]$. The results are compared and we observed a similar dependence between $\ensuremath{-}\ensuremath{\Delta}{\ensuremath{\rho}}_{\mathit{mag}}(T)$ and ${(T∕{T}_{C})}^{m}\ensuremath{\Delta}{S}_{\mathit{mag}}(T)$ with $m=0$ for $T\ensuremath{\geqslant}{T}_{C}$ and $m=1$ for $T\ensuremath{\leqslant}{T}_{C}$. 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, $\ensuremath{-}\ensuremath{\Delta}{S}_{\mathit{mag}}(T)$ and $\ensuremath{-}\ensuremath{\Delta}{\ensuremath{\rho}}_{\mathit{mag}}(T)$, 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. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|