Uniform spin wave modes in antiferromagnetic nanoparticles with uncompensated moments

Bahl, Christian; Garde, J.; Lefmann, Kim; Jensen, Thomas Bagger Stibius; Lindgård, Per‐Anker; Madsen, Daniel Esmarch; Mørup, Steen

doi:10.1140/epjb/e2008-00122-1

Cited by 15 publications

(15 citation statements)

References 30 publications

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“…This spin re-orientation is down to a change in sign of the overall anisotropy of the system made up of κ 1 and κ 2 (Eq. (1)), [15][16][17] where κ 1 is related to the anisotropy constant of the (111) direction (the (001) hexagonal direction) and κ 2 is related to the uniaxial anisotropy constant in the basal plane and is positive:…”

Section: A Properties Of "Bulk" α-Fe 2 Omentioning

confidence: 99%

Magnetic properties of nano-scale hematite, α-Fe2O3, studied by time-of-flight inelastic neutron spectroscopy

Hill

Jacobsen

Stewart

et al. 2014

The Journal of Chemical Physics

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Samples of nanoscale hematite, α-Fe 2 O 3 , with different surface geometries and properties have been studied with inelastic time-of-flight neutron scattering. The 15 nm diameter nanoparticles previously shown to have two collective magnetic excitation modes in separate triple-axis neutron scattering studies have been studied in further detail using the advantage of a large detector area, high resolution, and large energy transfer range of the IN5 TOF spectrometer. A mesoporous hematite sample has also been studied, showing similarities to that of the nanoparticle sample and bulk α-Fe 2 O 3 . Analysis of these modes provides temperature dependence of the magnetic anisotropy coefficient along the c-axis, κ 1 . This is shown to remain negative throughout the temperature range studied in both samples, providing an explanation for the previously observed suppression of the Morin transition in the mesoporous material. The values of this anisotropy coefficient are found to lie between those of bulk and nano-particulate samples, showing the hybrid nature of the mesoporous 3-dimensional structure. © 2014 AIP Publishing LLC. [http://dx

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Section: A Properties Of "Bulk" α-Fe 2 Omentioning

confidence: 99%

Magnetic properties of nano-scale hematite, α-Fe2O3, studied by time-of-flight inelastic neutron spectroscopy

Hill

Jacobsen

Stewart

et al. 2014

The Journal of Chemical Physics

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“…Indeed, nanoparticles of AFM materials have non-zero magnetic moments and are therefore, strictly speaking, not AFM. [22][23][24][25] Numerous magnetization studies of AFM nanoparticles have shown that both the initial susceptibility and the magnetization in large applied fields are considerably larger than in the corresponding bulk materials. Néel justified this result due to the finite number of magnetic atoms in the nanoparticles, which may lead to a difference in the numbers of spins in the two sublattices because of the random occupancy of lattice sites.…”

Section: View Article Onlinementioning

confidence: 99%

Interplay of chemical structure and magnetic order coupling at the interface between Cr₂O₃ and Fe₃O₄ in hybrid nanocomposites

Otero‐Lorenzo

Weber

Thomas

et al. 2014

Phys. Chem. Chem. Phys.

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“…Considering only motion with small deviations from the minimum energy configuration, we obtain two normal modes with frequencies [7] …”

Section: Analytical Theorymentioning

confidence: 99%

“…The method was tested against analytical results in the limit of vanishing fluctuation and dissipation [7,19], and for the one-sublattice (ferromagnetic) case [27,31].…”

Section: The Fluctuating Field Is Uncorrelated In Time B(t)b(t ) ∝ δmentioning

confidence: 99%

“…The magnetic dynamics of antiferromagnetic (AFM) nanoparticles has attracted much attention, because it displays much richer intrinsic dynamics than that of ferromagnetic nanoparticles [6], and because complications due to dipolar interactions between particles can be neglected. In AFM nanoparticles with uniaxial anisotropy, the uniform precession * lefmann@nbi.ku.dk mode resembles a q = 0 AFM spin wave, and its frequency is influenced both by the anisotropy and by the strength of the magnetic exchange interaction [7].…”

Section: Introductionmentioning

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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Uniform spin wave modes in antiferromagnetic nanoparticles with uncompensated moments

Cited by 15 publications

References 30 publications

Magnetic properties of nano-scale hematite, α-Fe2O3, studied by time-of-flight inelastic neutron spectroscopy

Magnetic properties of nano-scale hematite, α-Fe2O3, studied by time-of-flight inelastic neutron spectroscopy

Interplay of chemical structure and magnetic order coupling at the interface between Cr₂O₃ and Fe₃O₄ in hybrid nanocomposites

Dynamic rotor mode in antiferromagnetic nanoparticles

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Uniform spin wave modes in antiferromagnetic nanoparticles with uncompensated moments

Cited by 15 publications

References 30 publications

Magnetic properties of nano-scale hematite, α-Fe2O3, studied by time-of-flight inelastic neutron spectroscopy

Magnetic properties of nano-scale hematite, α-Fe2O3, studied by time-of-flight inelastic neutron spectroscopy

Interplay of chemical structure and magnetic order coupling at the interface between Cr2O3 and Fe3O4 in hybrid nanocomposites

Dynamic rotor mode in antiferromagnetic nanoparticles

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Interplay of chemical structure and magnetic order coupling at the interface between Cr₂O₃ and Fe₃O₄ in hybrid nanocomposites