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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Proton nuclear magnetic resonance investigation of the spin dynamics in cobalt based one-dimensional magnetic molecular chains

A. Lascialfari, E. Micotti, S. Aldrovandi, A. Caneschi, and D. Gatteschi

J. Appl. Phys. 93, 8749 (2003); http://dx.doi.org/10.1063/1.1558597 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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1H nuclear magnetic resonance was used to investigate the spin dynamics of the molecular chain Co(hfac)2NITPhOMe. This helical chain is composed of alternating Co(II) ions and radical moieties with dominant nearest-neighbor antiferromagnetic interaction (J∼220 K). Below 50 K, the chain behaves as a 1/2–1/2 Ising chain, with the electronic spins freezing before a transition to three-dimensional order. Previous results stated that the relaxation time τM of the magnetization M follows a thermally activated mechanism τM=τ0 exp(Δ/T) with τ0≈3(±1)×10−11 s and Δ≈152(±2) K. Measurements of the 1H NMR spin-lattice relaxation rate T1−1 were performed as a function of the temperature for two different external magnetic fields (0.35 and 1.7 T). Below 50 K, where the 1/2–1/2 spin chain approximation is valid, explanation of the experimental data was found by assuming the presence of two thermally activated relaxation mechanisms. One of these corresponds to the correlation time detected by M while a second mechanism, undetected in the magnetization measurements, becomes effective in the low temperature range. The possibility of the two nuclear relaxation mechanisms being related to different spin dynamics of the Co(II) and the radical spins, respectively, is discussed. © 2003 American Institute of Physics.
Show PACS
75.50.Xx Molecular magnets
76.60.Es Relaxation effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Ds Spin waves
75.30.Wx Spin crossover
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Dual pumping of magnetostatic and spin-wave modes in yttrium–iron–garnet spheres

W. Araújo, F. M. de Aguiar, A. Azevedo, and S. M. Rezende

J. Appl. Phys. 93, 8752 (2003); http://dx.doi.org/10.1063/1.1539079 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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In ferrimagnetic materials subjected to a static magnetic field H, a parallel rf magnetic field h gives rise to nonlinear absorption due to the unstable growth of certain spin waves when exceeding a parametric instability threshold (PIT), h=hc. The excited spin waves have half the pumping frequency and a wave number k that depends on H, such that the curve hc vs H resembles the Greek symbol ν and is thus called a “butterfly curve.” Recent experiments in a yttrium–iron–garnet sphere have shown that the PIT is resonantly reduced in the presence of a simultaneous perpendicular rf field at half the parallel-pumping frequency only on the right wing of the butterfly curve, where “volume” magnetostatic modes (k∼0) are primarily excited. Here, dual pumping experiments are reported at lower frequencies (8.882 and 4.441 GHz), allowing the presence of “surface” magnetostatic modes on the left wing and corresponding resonant PIT reduction in that region, where spin waves with k∼105 cm−1 are primarily excited by the parallel-pumping field. The results qualitatively agree with a model that put no restriction on the pumping frequency, thus extending earlier calculations by White and Schlömann [R. M. White and Schlömann, J. Appl. Phys. 33, 2437 (1962)]. © 2003 American Institute of Physics.
Show PACS
75.50.Gg Ferrimagnetics
75.30.Ds Spin waves
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Rf Surface magnetism

Magnetization reversal and aftereffect in orthoferrites

Y. S. Didosyan, H. Hauser, G. A. Reider, R. Glatz, and H. Wolfmayr

J. Appl. Phys. 93, 8755 (2003); http://dx.doi.org/10.1063/1.1558598 (3 pages) | Cited 7 times

Online Publication Date: 9 May 2003

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A magnetic aftereffect of several μs duration has been discovered in 1.2 mm thick samples of yttrium orthoferrite crystals cut perpendicularly to the optical axis at 1.3 μm wavelength. The aftereffect is associated with nucleation and expansion of oppositely magnetized domains that occur in a monodomain sample after removal of an external magnetic field. Magnetization reversal processes are visualized in a Faraday setup and studied by measuring the temporal dependence of the state of polarization of a transmitted light beam. © 2003 American Institute of Physics.
Show PACS
75.50.Gg Ferrimagnetics
75.60.Jk Magnetization reversal mechanisms
75.60.Lr Magnetic aftereffects
75.60.Ch Domain walls and domain structure
78.20.Ls Magneto-optical effects

Formation of envelope solitons from parametrically amplified and conjugated spin wave pulses

A. A. Serga, S. O. Demokritov, B. Hillebrands, and A. N. Slavin

J. Appl. Phys. 93, 8758 (2003); http://dx.doi.org/10.1063/1.1558603 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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Formation of dipolar spin wave envelope solitons from input pulses parametrically amplified by microwave pumping has been investigated experimentally in an axially magnetized yttrium–iron–garnet (YIG) film waveguide by means of the space- and time-resolved Brillouin light scattering technique. The interaction of a linear input spin wave packet with double-frequency microwave pumping leads to the formation of two parametrically amplified contrapropagating wave packets: forward and phase-conjugated reversed. It was found that both forward and reversed packets immediately after the interaction with pumping increase their lengths almost two times compared to the length of the input packet. In the course of further propagation both wave packets demonstrate a significant compression in length (up to 2.5 times) which depends on the power of the input signal and is a clear signature of envelope soliton formation. © 2003 American Institute of Physics.
Show PACS
75.30.Ds Spin waves
75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
78.35.+c Brillouin and Rayleigh scattering; other light scattering
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