Heat capacity of magnetite in the range 0.3 to 10 K

Jw, Koenitzer; Keesom, P. H.; Jm, Honig

doi:10.1103/physrevb.39.6231

Cited by 20 publications

(12 citation statements)

References 12 publications

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“…Based on the simple assumption that the hopping conductivity indefinitely decreases with decreasing size and saturates to the bulk value with increasing size, we adopt a phenomenological formula of , where E P,bulk and T 2,bulk are the polaron-binding energy and T 2 in bulk, respectively. A linear fit of our data with the reported values (θ D ≈ 500 K, 38 E P ≈ 200 meV, 39 and T 2,bulk ≈ 30 ms 18 ) gives α ≈ 0.54 and d c ≈ 8.3 nm. The exponent α decreases and the critical size d c increases as T 2,bulk increases.…”

supporting

confidence: 64%

“…Then, for d > d c , the nanocrystals should satisfy the following equation: , where E P,bulk and T 2,bulk are the polaron-binding energy and T 2 in bulk, respectively. A linear fit of our data with the reported values (θ D ≈ 500 K, E P ≈ 200 meV, and T 2,bulk ≈ 30 ms) gives α ≈ 0.54 and d c ≈ 8.3 nm. The exponent α decreases and the critical size d c increases as T 2,bulk increases.…”

supporting

confidence: 63%

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Microscopic States and the Verwey Transition of Magnetite Nanocrystals Investigated by Nuclear Magnetic Resonance

et al. 2018

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Fe nuclear magnetic resonance (NMR) of magnetite nanocrystals ranging in size from 7 nm to 7 μm is measured. The line width of the NMR spectra changes drastically around 120 K, showing microscopic evidence of the Verwey transition. In the region above the transition temperature, the line width of the spectrum increases and the spin-spin relaxation time decreases as the nanocrystal size decreases. The line-width broadening indicates the significant deformation of magnetic structure and reduction of charge order compared to bulk crystals, even when the structural distortion is unobservable. The reduction of the spin-spin relaxation time is attributed to the suppressed polaron hopping conductivity in ferromagnetic metals, which is a consequence of the enhanced electron-phonon coupling in the quantum-confinement regime. Our results show that the magnetic distortion occurs in the entire nanocrystal and does not comply with the simple model of the core-shell binary structure with a sharp boundary.

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supporting

confidence: 64%

supporting

confidence: 63%

Microscopic States and the Verwey Transition of Magnetite Nanocrystals Investigated by Nuclear Magnetic Resonance

et al. 2018

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“…The heat capacities of type I and II materials differ significantly below their respective Τv values down to the lowest measured temperatures, as shown in Fig. 10 [20,22]. This trend is also mirrored in the Debye θ values extracted from such measurements.…”

Section: Transitions Of Variable Order In Magnetitesupporting

confidence: 54%

Correlation-Driven Metal-Insulator Transitions

Honig

2000

Acta Phys. Pol. A

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“…Lattice vacancies are generally determined using redox titrations or thermogravimetric analysis (TGA) [53][54][55][56][57][58][59], but for nanomaterials and materials with very few vacancies, less conventional methods are required such as EXAFS [60,61], XANES [61], other X-ray techniques [53,61], Raman spectroscopy [60,61], high resolution TEM [61], EELS [62], XEDS [63], STEM [64], neutron diffraction [53,59], and a plethora of esoteric techniques [65][66][67][68][69][70][71][72][73].…”

Section: B Lattice Vacanciesmentioning

confidence: 99%

Lattice vacancies responsible for the linear dependence of the low-temperature heat capacity of insulating materials

Schliesser

Woodfield

2015

Phys. Rev. B

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The linear dependence on temperature (γT) of the heat capacity at low temperatures (T < 15 K) is traditionally attributed to conduction electrons in metals; however, many insulators also exhibit a linear dependence that has been attributed to a variety of other physical properties. The property most commonly used to justify the presence of this linear dependence is lattice vacancies, but a correlation between these two properties has never been shown. We have devised a theory that justifies a linear heat capacity as a result of lattice vacancies, and we provide measured values and data from the literature to support our arguments. We postulate that many small Schottky anomalies are produced by a puckering of the lattice around these vacancies, and variations in the lattice caused by position or proximity to some form of structure result in a distribution of Schottky anomalies with different energies. We present a mathematical model to describe these anomalies and their distribution based on literature data that ultimately results in a linear heat capacity. From these calculations, a quantitative relationship between the linear term and the concentration of lattice vacancies is identified, and we verify these calculations using values of γ and vacancy concentrations for several materials. We have compiled many values of γ and vacancy concentrations from the literature which show several significant trends that provide further evidence for our theory.

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Heat capacity of magnetite in the range 0.3 to 10 K

Cited by 20 publications

References 12 publications

Microscopic States and the Verwey Transition of Magnetite Nanocrystals Investigated by Nuclear Magnetic Resonance

Microscopic States and the Verwey Transition of Magnetite Nanocrystals Investigated by Nuclear Magnetic Resonance

Correlation-Driven Metal-Insulator Transitions

Lattice vacancies responsible for the linear dependence of the low-temperature heat capacity of insulating materials

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