Efeito de substituiÃÃo atÃmica no calor especÃfico da L-arginina fosfatada monohidratada e do FexZn1-xF2

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

A Physical Properties Measurement System â PPMS was assembled to perform heat capacity (Cp) measurements in the temperature range 1.8 â 390 K. The system was used to investigate the temperature dependence of Cp in samples of L-arginine phosphate monohydrated (LAP) at low temperatures. The measurements were carried out in pure LAP and in doped samples: Cu(0.25%), Fe(0.025%), Mn(0.005%) and Ni(0.075%). It was observed a temperature dependent excess in the heat capacity of the pure LAP sample. It was also found that this contribution increased is higher in the doped samples. Moreover, we were able to account for the temperature dependence of Cp using a model that included the Debye contribution, an Einstein term and a contribution due interstitial defects thermally created. The experimental data were fitted by the model yielding the Debye temperature (θD = 160 K), the energy required to created the defects (157.9 meV), the number of independent harmonic oscillators (Einstein term) and the number of defect present in each sample. The PPMS was also used to study the effect produced by replacing magnetic ions (Fe) by the non-magnetic Zn ion in the heat capacity of FeF2.The family of samples of FexZn1- xF2 investigated in the present work is of great interest for presenting the so called randomfield phenomenon. The measurements were done in thin slabs of samples with concentration in the range of 0.26 â 1. The measurements allowed us to follow the NÃel temperature TN(x) down to near the percolation concentration (xp = 0.24). It was observed that TN(x) presents a non-linear dependence in x. For 0.4

ASSUNTO(S)

specific heat l-arginina campo aleatÃrio l-arginine random-field fisica substitutional disorder desordem substitucional antiferromagnet antiferromagneto calor especÃfico

ACESSO AO ARTIGO

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