First principles electronic structure of spinel LiCr2O4: A possible half-metal?

We have employed first-principles electronic structure calculations to examine the hypothetical (but plausible) oxide spinel, LiCr2O4 with the d^{2.5} electronic configuration. The cell (cubic) and internal (oxygen position) structural parameters have been obtained for this compound through structural relaxation in the first-principles framework. Within the one-electron band picture, we find that LiCr2O4 is magnetic, and a candidate half-metal. The electronic structure is substantially different from the closely related and well known rutile half-metal CrO2. In particular, we find a smaller conduction band width in the spinel compound, perhaps as a result of the distinct topology of the spinel crystal structure, and the reduced oxidation state. The magnetism and half-metallicity of LiCr2O4 has been mapped in the parameter space of its cubic crystal structure. Comparisons with superconducting LiTi2O4 (d^{0.5}), heavy-fermion LiV2O4 (d^{1.5}) and charge-ordering LiMn2O4 (d^{3.5}) suggest the effectiveness of a nearly-rigid band picture involving simple shifts of the position of E_F in these very different materials. Comparisons are also made with the electronic structure of ZnV2O4 (d^{2}), a correlated insulator that undergoes a structural and antiferromagnetic phase transition.Comment: 9 pages, 7 Figures, version as published in PR

Utilização de resíduo agroindustrial de abacaxi desidratado em dietas para caprinos em crescimento: digestibilidade e desempenho Use of dehydrated pineapple by-product in diets for growing goats: digestibility and performance

Avaliou-se o efeito da substituição do feno de coastcross (Cynodon dactylon) pelo resíduo agroindustrial de abacaxi desidratado sobre o desempenho, a digestibilidade aparente e o consumo de nutrientes digestíveis em caprinos em crescimento. Foram utilizadas 24 fêmeas mestiças Saanen x Crioula com peso vivo médio inicial de 19,2 kg, em um delineamento inteiramente casualizado, com quatro tratamentos, representados pelos níveis de 0, 33, 66 e 100% de inclusão de resíduo agroindustrial de abacaxi desidratado (RAD) em substituição ao feno de coastcross. Não houve efeito dos níveis de substituição sobre os coeficientes de digestibilidade aparente da MS, PB e FDN. A digestibilidade da MO e celulose (CEL) aumentaram linearmente, enquanto a da FDA apresentou efeito quadrático. Os consumos médios de nutrientes digestíveis, em g/kgPV0,75, para os níveis de substituição de 0, 33, 66 e 100% foram, respectivamente, de 62,35; 63,58; 59,53 e 54,47 (MS), 60,40; 61,51; 57,94 e 51,83 (MO), 7,91; 7,86; 7,27 e 6,44 (PB), 24,85; 22,94; 21,61 e 18,75 (FDN), 7,62; 5,30; 5,96 e 7,11 (FDA) e 37,62; 27,83; 32,91 e 31,98 (CEL), resultando em ganhos de peso de 204, 215, 198 e 196 g/dia. A utilização de resíduo agroindustrial de abacaxi desidratado em rações para caprinos melhora os coeficientes de digestibilidade de MO, CEL e FDA e proporciona ganhos de peso satisfatórios em fêmeas em crescimento.<br>The objective of this study was to evaluate the effect of replacing coastcross (Cynodon dactylon) hay with a dehydrated pineapple by-product (DPB) on performance, apparent digestibility, and intake of digestible nutrients in growing goats. Twenty-four crossbred Saanen x Criola female goats averaging 19.2 kg of body weight (BW) at the beginning of the trial were used in a completely randomized design. Animals were assigned to one of the following four treatments: 0, 33, 66, or 100% of DPB in the diet. Replacing coastcross hay with DPB did not significantly affect the apparent digestibility of dry matter (DM), crude protein (CP), and neutral detergent fiber (NDF). However, the apparent digestibility of both organic matter (OM) and cellulose (CEL) increased linearly while that of acid detergent fiber (ADF) showed a quadratic effect with the increasing levels of DPB in the diet. The average intake of digestible nutrients, expressed in g/kg BW0.75, for treatments with 0, 33, 66, or 100% of dietary DPB were in this order: 62.35, 63.58, 59.53 and 54.47 for DM; 60.40, 61.51, 57.94 and 51.83 for OM; 7.91, 7.86, 7.27 and 6.44 for CP; 24.85, 22.94, 21.61 and 18.75 for NDF; 7.62, 5.30, 5.96 and 7.11 for ADF; and 37.62, 27.83, 32.91 and 31.98 for CEL. Replacing coastcross hay by DPB in the diet improved the apparent digestibility of OM, CEL, and ADF and resulted in BW that was considered satisfactory for growing female goats