1,454 research outputs found

    Spin-1/2 Triangular Lattice with Orbital Degeneracy in a Metallic Oxide Ag2NiO2

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    A novel metallic and magnetic transition metal oxide Ag2NiO2 is studied by means of resistivity, magnetic susceptibility, specific heat and X-ray diffraction. The crystal structure is characterized by alternating stacking of a Ni3+O2 layer and a (Ag2)+ layer, the former realizing a spin-1/2 triangular lattice with eg orbital degeneracy and the latter providing itinerant electrons. It is found that the NiO2 layer exhibits orbital ordering at Ts = 260 K and antiferromagnetic spin ordering at TN = 56 K. Moreover, a moderately large mass enhancement is found for the itinerant electrons, suggesting a significant contribution from the nearly localized Ni 3d state to the Ag 5s state that forms a broad band.Comment: 9 pages, 5 figures, to be published in Rapid Communications, Phys. Rev.

    Activation volumes in CoPtCr-SiO2 perpendicular recording media

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    CoPtCr-SiO2 perpendicular recording media with varying levels of SiO2 were examined by two different methods to determine the activation volume. The first is based on the sweep-rate dependence of the remanence coercivity using Sharrock's equation. The second is based on the measurement of the fluctuation field from time-dependence data, determined using a magneto-optical Kerr effect (MOKE) magnetometer. The values of V-act measured at the coercivity for both methods are almost the same, with the fluctuation field and activation volumes increasing with the SiO2 content. The difference between V-act and the grain volume measured directly from bright-field TEM images decreases as the SiO2 content increases due to the reduction of intergranular exchange coupling. The experimental results indicate that values of V-act obtained from single- and double-layered media are consistent. It was also found that the coercivity and normalized hysteresis loop slope at coercivity varied with SiO2 content, with the coercivity peaking at 8 at % SiO2 (nearly 26 vol% SiO2)

    Efeitos da adubação foliar do feijoeiro (Phaseolus vulgaris, L.) durante o estádio da formação dos grãos

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    An experiment was carried out with common bean (Phaseolus vulgaris, L.) in a Red Yellow Latossol, sandy phase, in order to study the influence of foliar spraying of the Hanway nutrient solution (NPKS) at grain filling stage on: 1) grain yield; 2) the uptake of fertilizer and soil nitrogen by this crop through the root system and 3) the efficiency of utilization of the nitrogen in the foliar spray solution by the grain. The results of this experiment showed that the foliar application of the Hanway solution with ammonium nitrate at the pod filling period caused severe leaf burn and grain yield was inferior to that of the plants which received a soil application of this fertilizer at the same stage. These facts can be attributed to the presence of ammonium nitrate in the concentration used. The composition of final spray was: 114,28 Kg NH4NO3 + 43,11 Kg potassium poliphosphate + 12,44 Kg potassium sulphate per 500 litres. The uptake of nitrogen fertilizer through the root system and the efficiency of its utilization was greater than that through the leaves.Urn experimento foi conduzido com feijoeiro (Phaseolus vulgaris, L.) num latossol vermelho amarelo, fase arenosa, a fim de estudar a influência da pulverização foliar de solução de nutrientes (NPKS) durante o estádio da formação de grão na: 1) produção; 2) absorção de nitrogênio do solo e do fertilizante pela cultura através do sistema radicular e 3) a eficiência pelo grão de utilização de nitrogênio contido na solução de nutrientes pulverizada. A composição da solução era: 114,28 kg NH4NO3 + 43,11 Kg polifosfato de potássio + 12,44 kg de sulfato de potássio por 500 litros. Os resultados deste experimento mostraram que a aplicação foliar desta solução de Hanway com nitrato de amônio em lugar de uréia, durante o estádio da formação de grão, causou queima da folha e a produção de grãos foi inferior àquela das plantas que receberam uma aplicação no solo de fertilizante nitrogenado no mesmo estádio. Esses fatos podem ser atribuídos a presença de nitrato de amônio na concentração usada. A absorção do nitrogênio do fertilizante através do sistema radicular e a eficiência da sua utilização foi maior do que daquela através das folhas

    Efeito do período do dia da pulverização foliar de várias doses de soluções NPKS no feijoeiro (Phaseolus vulgaris, L)

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    An experiment was carried out in order to determine the effect of day time of foliar spraying of several levels of nitrogen fertilizers, N-P-K-S station, and its components on common bean leaves. Results, based on the visual observations, indicated the maximum levels of each fertilizer that did not cause injuries and showed that the foliar spraying early in the morning is the best day time.Um experimento foi levado a efeito, para determinar o efeito do período do dia na pulverização foliar de várias doses de fontes de nitrogênio, da solução de nutrientes de Hanway e seus componentes, nas folhas do feijoeiro. Os resultados, baseados em observações visuais, indicaram os níveis de cada fertilizante utilizado na pulverização que não causou injurias, sendo o período da manhã, entre 6 e 7 horas, o melhor

    Room temperature ferromagnetic behavior in the hollandite-type titanium oxide

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    A hollandite-type K(x)Ti(8)O(16) polycrystalline sample has been prepared and studied by magnetization, resistivity and x-ray photoelectron spectroscopy (XPS). Room temperature ferromagnetic behavior is observed in the magnetic hysteresis measurement. The sample shows a semiconductive temperature dependence in the resistivity measurement. Analysis of the Ti 2p(3/2) core-level XPS spectrum indicates that the titanium ions have a mixed valence of Ti(4+) and Ti(3+). In addition, the valence band spectrum reveals that the 3d electrons tend to localize on Ti(3+) ions in the hollandite-type TiO(2) lattice. Also, analysis of the valence band spectrum shows that the prepared sample is a wide-gap oxide with a band gap of 3.6 eV. These results indicate that the present hollandite-type K(x)Ti(8)O(16) sample can be classified as a TiO(2)-based wide-gap semiconductor with Curie temperature above room temperature. Room temperature ferromagnetism (RTFM) decreases in the sample prepared under a strong reducing gas atmosphere, accompanied with the decrease in the resistivity. The results imply that the localized 3d electrons are responsible for the RTFM of the K(x)Ti(8)O(16) sample

    Avaliação agronômica de fertilizantes fosfatados em solos do Estado do Pará.

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    Switching field and thermal stability of CoPt/Ru dot arrays with various thicknesses

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    The switching fields and thermal stability of CoPt/Ru dot arrays with various dot thickness delta (5-20 nm) were experimentally investigated as a function of the dot diameter, D, (130-300 nm). All dot arrays showed a single domain state, even after removal of an applied field equal to the remanence coercivity Hr. The angular dependence of Hr for the dot arrays indicated coherent rotation of the magnetization during nucleation. We estimated the values of the "intrinsic" remanence coercivity H0 obtained by subtracting the effect of thermal agitation on the magnetization and the stabilizing energy barrier to nucleation E0/(kBT). The variation in H0 as a function of delta and D was qualitatively in good agreement with that of the effective anisotropy field at the dot center Hk eff(r=0), calculated taking account of the demagnetizing field in the dots. The ratio of H 0 to Hk eff(r=0) for the dot arrays with delta=10 nm increased from 0.53 to 0.70 as D decreased from 300 to 140 nm, and no significant difference in the H0/Hk eff(r=0) ratio due to the difference in delta was observed. On the other hand, E0/(k BT) decreased as delta decreased. E0/(kBT) increased slightly as D decreased, but, was not so sensitive to D over the present D rang

    Forming method and characteristics of coiled spring in small coil diameter and with high rectangular ratio in winding wire cross section

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    This paper presents a new forming method of a coiled spring which is used as a forceps manipulator of a surgical robot. Joint parts of forceps manipulator are required to be “easy to bend and strong to twist”. This demand is fulfilled by using coiled springs with high rectangular ratio in winding wire cross section. However, the coiled springs are conventionally expensive as they are fabricated by machining. This study proposed a new and inexpensive forming method for fabrication of the coiled spring with high rectangular ratio in the wire cross section. In this method, the coiled spring with circular shape in the winding wire cross section is compressed in the coil axial direction by upsetting, and then the rectangle ratio of the wire becomes high. The coiled spring with a high rectangular ratio of 3 was obtained by the proposed method. In addition, a numerical analysis and an experiment were conducted for evaluation of the formed coiled springs in terms of tensile, torsional, and bending characteristics. The formed coiled springs were easy to bend and strong to twist from results. Moreover, the elastic limit of the formed coiled springs improved due to work hardening by upsetting
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