64,758 research outputs found
Metallic Continuum Quantum Ferromagnets at Finite Temperature
We study via renormalization group (RG) and large N methods the problem of
continuum SU(N) quantum Heisenberg ferromagnets (QHF) coupled to gapless
electrons. We establish the phase diagram of the dissipative problem and
investigate the changes in the Curie temperature, magnetization, and magnetic
correlation length due to dissipation and both thermal and quantum
fluctuations. We show that the interplay between the topological term (Berry's
phase) and dissipation leads to non-trivial effects for the finite temperature
critical behavior.Comment: Corrected typos, new discussion of T=0 results, to appear in
Europhys. Let
Metamasius sp. (Coleoptera, Curculionidae) vetor do Rhadinaphelenchus cocophilus agente causador do anel vermelho do dendezeiro.
A doença conhecida com Anel Vermelho é de grande importância para o cultivo do dendezeiro, por causar a morte das plantas afetadas. Na Bahia, a doença já causou perdas acima de 50% do stand de algumas plantações, e, no Estado do Pará vem se alastrando gradativamente, chegando a ser a doença mais importante em várias localidades.bitstream/item/61701/1/Belem-PA17.pd
Tunable asymmetric magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films
We investigate the magnetization dynamics through the magnetoimpedance effect
in ferromagnetic NiFe/Cu/Co films. We observe that the magnetoimpedance
response is dependent on the thickness of the non-magnetic Cu spacer material,
a fact associated to the kind of the magnetic interaction between the
ferromagnetic layers. Thus, we present an experimental study on asymmetric
magnetoimpedance in ferromagnetic films with biphase magnetic behavior and
explore the possibility of tuning the linear region of the magnetoimpedance
curves around zero magnetic field by varying the thickness of the non-magnetic
spacer material, and probe current frequency. We discuss the experimental
magnetoimpedance results in terms of the different mechanisms governing the
magnetization dynamics at distinct frequency ranges, quasi-static magnetic
properties, thickness of the non-magnetic spacer material, and the kind of the
magnetic interaction between the ferromagnetic layers. The results place
ferromagnetic films with biphase magnetic behavior exhibiting asymmetric
magnetoimpedance effect as a very attractive candidate for application as probe
element in the development of auto-biased linear magnetic field sensors.Comment: 5 figure
Frequency Modulation of Spin-Transfer Oscillators
Spin-polarized dc electric current flowing into a magnetic layer can induce
precession of the magnetization at a frequency that depends on current. We show
that addition of an ac current to this dc bias current results in a frequency
modulated (FM) spectral output, generating sidebands spaced at the modulation
frequency. The sideband amplitudes and shift of the center frequency with drive
amplitude are in good agreement with a nonlinear FM model that takes into
account the nonlinear frequency-current relation generally induced by spin
transfer. Single-domain simulations show that ac current modulates the cone
angle of the magnetization precession, in turn modulating the frequency via the
demagnetizing field. These results are promising for communications and signal
processing applications of spin-transfer oscillators.Comment: 13 pages, 3 Figure
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