Thermal fluctuations of fine magnetic particles

Würger, Aloïs

doi:10.1209/epl/i1998-00442-2

Cited by 6 publications

(4 citation statements)

References 20 publications

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“…A derivation for the spectrum of a fluctuating ferromagnetic nanoparticle in a uniaxial anisotropy was earlier derived by Würger 24 . However, in this scenario, the frequency of the uniform modes decrease with increasing temperature, in contrary to our observations.…”

Section: Analytical Theorymentioning

confidence: 99%

“…To describe the low-energy dynamics, we follow Würger 24 and assume collective motion (q = 0) of the spins in each of the two sublattices (A and B). This is justified by the fact that the highest temperature in our study, 300 K, is far below the Néel temperature of the system and therefore the spin waves have reduced the ordered moment of the sublattices only slightly.…”

Section: Analytical Theorymentioning

confidence: 99%

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Dynamic rotor mode in antiferromagnetic nanoparticles

et al. 2015

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We present experimental, numerical, and theoretical evidence for an unusual mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8-nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K. However, the signal from inelastic neutron scattering remains above that temperature, indicating a magnetic system in constant motion. In addition, the precession frequency of the inelastic magnetic signal shows an increase above 100 K. Numerical Langevin simulations of spin dynamics reproduce all measured neutron data and reveal that thermally activated spin canting gives rise to an unusual type of coherent magnetic precession mode. This "rotor" mode can be seen as a high-temperature version of superparamagnetism and is driven by exchange interactions between the two magnetic sublattices. The frequency of the rotor mode behaves in fair agreement with a simple analytical model, based on a high-temperature approximation of the generally accepted Hamiltonian of the system. The extracted model parameters, such as the magnetic interaction and the axial anisotropy, are in excellent agreement with results from Mössbauer spectroscopy.

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Section: Analytical Theorymentioning

confidence: 99%

Section: Analytical Theorymentioning

confidence: 99%

Dynamic rotor mode in antiferromagnetic nanoparticles

et al. 2015

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“…Then the two types of magnetic dynamics cannot be separated clearly, because the sublattice magnetization vectors can fluctuate with similar probabilities in all directions in or close to the (111) plane. The transition to this isotropic relaxation regime has been discussed by Würger [47]. For this reason, the data obtained above 250 K are not included in the fits.…”

Section: Temperature Dependence Of the Resonance Energymentioning

confidence: 99%

Spin dynamics in weakly and strongly interacting NiO nanoparticles

Bahl

Lefmann

Kuhn

et al. 2006

J. Phys.: Condens. Matter

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The spin dynamics of plate-shaped nanoparticles of NiO has been studied by inelastic neutron scattering and Mössbauer spectroscopy. A value of the in-plane anisotropy energy constant significantly larger than the bulk value has been measured. The temperature and field dependence of the energy of the antiferromagnetic resonance mode associated with this in-plane anisotropy has been studied. Both Mössbauer spectroscopy and neutron scattering data show that the magnetic fluctuations are strongly affected by the strength of interparticle interactions.

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“…A main goal of the paper is to understand the respective dynamics and relaxation of both the superparamagnetic fluctuations and the collective magnetic excitations with respect to the temperature T . Prior to the present work, theoretical studies have analytically shown that the superparamagnetic relaxation follows the simple Arrhenius behavior of ∼ Γ 0 (T )e −EB/T with a certain form of Γ 0 (T ), where E B the energy barrier, for FM grains (like Mn 12 O 12 molecules) [7,8,9]. At the very low temperatures (T < ∼ 2 K), however, it is found that the relaxation deviates from the Arrhenius law and is dominated by a resonant tunneling between low-lying states [10].…”

mentioning

confidence: 91%

Spin correlation, excitation, and relaxation of antiferromagnetic hematiteα−Fe2O3nanoparticles

Lee

2004

Phys. Rev. B

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We study the dynamics of spins in the canted antiferromagnetic hematite nanoparticles α-Fe2O3. The system includes an antiferromagnetic exchange (J) between two sublattices as well as the potential dominated by a uniaxial anisotropy and dissipates through the thermally triggered spinphonon mechanism. The exchange J is found to reduce the superparamagnetic relaxation and drive the incoherent relaxation of transverse spins in the low temperature. Dynamical properties are semiquantitatively understood within a role of the exchange interaction J and agree well with recent inelastic neutron scattering experiments.

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Thermal fluctuations of fine magnetic particles

Cited by 6 publications

References 20 publications

Dynamic rotor mode in antiferromagnetic nanoparticles

Dynamic rotor mode in antiferromagnetic nanoparticles

Spin dynamics in weakly and strongly interacting NiO nanoparticles

Spin correlation, excitation, and relaxation of antiferromagnetic hematiteα−Fe2O3nanoparticles

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