2,122 research outputs found
Quantum critical 5f-electrons avoid singularities in U(Ru,Rh)2Si2
We present specific heat measurements of 4% Rh-doped U(Ru,Rh)2Si2 at magnetic
fields above the proposed metamagnetic transition field Hm~34 T, revealing
striking similarities to the isotructural Ce analog CeRu2Si2, suggesting that
strongly renormalized hybridized band models apply equally well to both
systems. The vanishing bandwidths as H --> Hm are consistent with a putative
quantum critical point close to Hm. The existence of a phase transition into an
ordered phase in the vicinity of Hm for 4% Rh-doped U(Ru,Rh)2Si2, but not for
CeRu2Si2, is consistent with a stronger super-exchange in the case of the U 5-f
system, with irreversible processes at the transition revealing a strong
coupling of the 5f orbitals to the lattice, most suggestive of orbital or
electric quadrupolar order.Comment: 4 pages, 4 figure
High magnetic field thermal-expansion and elastic properties of CeRhIn
We report high magnetic field thermal-expansion and magnetostriction results
on CeRhIn single crystals. Several transitions, both first and second
order, are observed when the field is applied perpendicular to the
crystallographic c-axis. The magnetic field dependence of the thermal-expansion
coefficient above 15 K, where the magnetic correlations are negligible, can be
explained supposing an almost pure ground state doublet, in
apparent contradiction with neutron scattering experiments. Although the
spin-lattice interaction is relevant in this compound, the effect of the
magnetic correlations on the elastic properties is relatively weak, as revealed
by resonant ultrasound spectroscopy experiments.Comment: 5 pages, 6 figure
High-Field Properties of Single-Crystalline Cavo3
The magnetic properties of perovskite CaVO3 single crystals have been studied
by means of magnetoresistance r(T, H) and magnetization M(H) measurements in
fields to 18T. At 2 K, the magnetoresistance is positive and a maximum value of
Dr(18T)/r(0) = 16.5% is found for H//a. The magnetization exhibits a smooth
increase at 2 K, reaching values of M(18T) = 0.03, 0.05, 0.17 mB/f.u. for H//a,
H//b, and H//c, respectively. This anisotropy found in M(H) is consistent with
that observed for Dr(H//a) > Dr(H//b) > Dr(H//c). These results can be
interpreted in terms of the field-dependent scattering mechanism of CaVO3.Comment: 10 pages, including 3 figure
High-magnetic field lattice length changes in URu2Si2
We report high magnetic field (up to 45 T) c-axis thermal expansion and
magnetostriction experiments on URu2Si2 single crystals. The sample length
change associated with the transition to the hidden order phase becomes
increasingly discontinous as the magnetic field is raised above 25 T. The
re-entrant ordered phase III is clearly observed in both the thermal expansion
and magnetostriction above 36 T, in good agreement with previous results. The
sample length is also discontinuous at the boundaries of this phase, mainly at
the upper boundary. A change in the sign of the coefficient of
thermal-expansion is observed at the metamagnetic transition (B_M = 38 T) which
is likely related to the existence of a quantum critical end point.Comment: 5 pages, 4 figures, to be published in PR
Comportamento de cultivares de café em áreas infestadas por Meloidogyne exigua.
O Meloidogyne exigua é uma espécie de nematóide que provoca galhas no sistema radicular do cafeeiro, reduzindo a capacidade de absorção de nutrientes pela planta, o que leva ao seu depauperamento e pode resultar em reduções significativas de produtividade. Embora não seja a espécie mais agressiva, sua importância reside também na sua disseminação generalizada, uma vez que este nematóide pode ser encontrado nas principais regiões produtoras de café arábica. O presente trabalho teve como objetivo avaliar o comportamento de cultivares comerciais de café, bem como, o efeito da utilização de um inseticida-nematicida sobre a produtividade destas lavouras instaladas em área infestadas com o M. exigua. Os experimentos estão instalados em Carmo da Cachoeira e Três Pontas, Sul de Minas Gerais, em área com histórico da presença do nematóide M. exigua. Foram utilizadas dez cultivares de café, sendo seis consideradas resistentes ao nematóide, e as demais susceptíveis. Em metade das parcelas, foi aplicado o inseticida nematicida Terburfós na dose de 3g por planta por ocasião do plantio e, posteriormente, 30kg/ha/ano. Foi utilizado o delineamento experimental com blocos casualizados com três repetições e parcelas com três plantas. Até o momento, não foi observada diferenças significativas relativas ao desenvolvimento e produção das cultivares resistentes ou suscetíveis associadas ou não ao manejo fitossanitário com o inseticida-nematicida terbufós
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