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|Type:||Artigo de periódico|
|Title:||Magnetic Properties Of Cu(l-aspartato)(h2o)2: A Linear Chain Antiferromagnet|
|Abstract:||Specific heat, magnetic susceptibility, and magnetization measurements were performed in polycrystalline samples of the copper complex of the amino acid L-aspartic acid [called Cu(L-asp)]. The specific heat was measured between 3 and 45 K, while dc and ac susceptibilities were measured between 1.8 and 300 K. The magnetization data were obtained as a function of an applied field up to 9 T, at various fixed temperatures between 2 and 10 K. The specific heat and magnetic susceptibility curves show peaks at 3.95 K and 6.9 K, respectively, and approach zero at lower and higher temperatures. This behavior cannot be accounted for by considering only the superexchange paths provided by the σ skeleton of aspartic acid. If this were the case, a uniform J0 along the asp-Cu-asp-Cu-asp chains would be expected. The data were well fitted, proposing for Cu(L-asp) a behavior characteristic of an alternating linear chain antiferromagnet. Each S=1/2 copper ion is coupled with an isotropic exchange interaction J0/k=(-5.3±0.1) K with one copper neighbor in the chain, and αJ0/k=(-1.5±0.1) K with the other [α=(0.29±0.02)]. The average g value is g=2.165±0.002. Considering the alternating chain model, the susceptibility and magnetization data suggest also the presence of an additional interchain ferromagnetic coupling, which (within a mean-field approximation) leads to J′/k =(0.7±0.1) K. Other exchange paths are proposed to explain the data. An important finding is that hydrogen bonds may support relatively large values of J. ©1999 The American Physical Society.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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