Co57 and Fe57 mössbauer studies of the spinels FeCo2O4 and Fe0.5Co2.5O4

Smith, Paul A.; Spencer, Charles D.; Stillwell, R. P.

doi:10.1016/0022-3697(78)90208-1

Cited by 32 publications

(21 citation statements)

References 11 publications

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“…FeCo 2 O 4 is the only completely inverse spinel under equilibrium conditions, due to the highly exothermic process of inversion, which agrees with experimental evidence. 108,109 Nevertheless, our results for the Co-based oxide disagree with the equilibrium inversion degree of x = 0.565 and 0.605 obtained by means of fitting the dependence of the magnetic moment with x 39,106 and the similar values within the range 0.52 ≤ x ≤ 0.7 derived from Mössbauer spectra, 40,105,107 see Table III. Its sulfide counterpart, which has not been studied experimentally, shows an equilibrium inversion degree of x = 0.48 in our calculations.…”

Section: Fecr2s4contrasting

confidence: 90%

First-principles study of the inversion thermodynamics and electronic structure ofFeM2X4(thio)spinels (M=Cr, Mn, Co, Ni;
Santos‐Carballal
¹
,
Roldan
²
,
Grau‐Crespo
³

et al. 2015
Phys. Rev. B

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FeM 2 X 4 spinels, where M is a transition metal and X is oxygen or sulfur, are candidate materials for spin filters, one of the key devices in spintronics. We present here a computational study of the inversion thermodynamics and the electronic structure of these (thio)spinels for M = Cr, Mn, Co, Ni, using calculations based on the density functional theory with on-site Hubbard corrections (DFT+U). The analysis of the configurational free energies shows that different behaviour is expected for the equilibrium cation distributions in these structures: FeCr 2 X 4 and FeMn 2 S 4 are fully normal, FeNi 2 X 4 and FeCo 2 S 4 are intermediate, and FeCo 2 O 4 and FeMn 2 O 4 are fully inverted. We have analyzed the role played by the size of the ions and by the crystal field stabilization effects in determining the equilibrium inversion degree. We also discuss how the electronic and magnetic structure of these spinels is modified by the degree of inversion, assuming that this could be varied from the equilibrium value. We have obtained electronic densities of states for the completely normal and completely inverse cation distribution of each compound. FeCr 2 X 4 , FeMn 2 X 4 , FeCo 2 O 4 and FeNi 2 O 4 are half-metals in the ferrimagnetic state Accepted for publication in Physical Review B (2015) 2 when Fe is in tetrahedral positions. When M is filling the tetrahedral positions, the Cr-containing compounds and FeMn 2 O 4 are half-metallic systems, while the Co and Ni spinels are insulators. The Co and Ni sulfide counterparts are metallic for any inversion degree together with the inverse FeMn 2 S 4 . Our calculations suggest that the spin filtering properties of the FeM 2 X 4 (thio)spinels could be modified via the control of the cation distribution through variations in the synthesis conditions. PACS number(s): 75.50.Gg, 61.50.Ah, 61.66.Fn I. INTRODUCTIONThe electronics industry has been revolutionized over the last four decades due to the continuous miniaturization of integrated circuits. Spintronics, short for spin electronics, has emerged as the basis for the next generation of electronic devices. 1 The concept of spintronics is to take advantage of both the electron charge and spin in solid-state systems, and therefore its applications require magnetic materials with highly spin-polarized electrons at the Fermi energy. 2 This can be achieved by half-metallic ferrimagnets (HMF) 3 with Curie temperature higher than room temperature. The spin-polarized density of states (DOS) of these compounds has a marked asymmetry around the Fermi energy, where one of the spin channels is a conductor while the other one behaves as an insulator, 4 making them electronic spin filters. Spintronic applications are based on spin valves, 5,6 where two HMF layers are sandwiching a non-magnetic layer. In spintronic applications of high efficiency, the resistivity of the spin valve is required to be extremely sensible to the magnetic field (magnetoresistance). 1The magnetoresistive behavior, 7,8 and the half-metallic and ferrimagnetic 9-12 ...

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Section: Fecr2s4contrasting

confidence: 90%

First-principles study of the inversion thermodynamics and electronic structure ofFeM2X4(thio)spinels (M=Cr, Mn, Co, Ni;
Santos‐Carballal
¹
,
Roldan
²
,
Grau‐Crespo
³

et al. 2015
Phys. Rev. B

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“…It may be mentioned that we did not find any significant change in the XRD spectrum when slow cooled sample is compared with the direct air quenched samples. Smith et al [24] has reported the same effect from X-ray diffraction and Mössbauer measurements.…”

Section: Resultsmentioning

confidence: 61%

“…A few works may be mentioned here, which indicated that the distribution of cations in Co 2 FeO 4 is very much sensitive on the preparation techniques. Murray et al [23] [24], Magnetic measurement [25] and Neutron diffraction study [22], the estimated distribution of cations in Co 2 FeO [16][17][18]26] indicated an increase of band gap energy (0.14 eV to 1.1 eV) with the increase of Co content in Fe 3-x Co x O 4 . It is also noted that Co 2 FeO 4 is prepared in most of the reports using different chemical methods, e.g., coprecipitation [21,27] and combustion reaction [28].…”

Section: Introductionmentioning

confidence: 99%

Structural phase stability and magnetism in Co2FeO4 spinel oxide

Muthuselvam

Bhowmik

2009

Solid State Sciences

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We report a correlation between structural phase stability and magnetic properties of Co 2 FeO 4 spinel oxide. We employed mechanical alloying and subsequent annealing to obtain the desired samples. The particle size of the samples changes from 25 nm to 45 nm. The structural phase separation of samples, except sample annealed at 900 0 C, into Co rich and Fe rich spinel phase has been examined from XRD spectrum, SEM picture, along with EDAX spectrum, and magnetic measurements. The present study indicated the ferrimagnetic character of Co 2 FeO 4 , irrespective of structural phase stability. The observation of mixed ferrimagnetic phases, associated with two Curie temperatures at T C1 and T C2 (>T C1 ), respectively, provides the additional support of the splitting of single cubic spinel phase in Co 2 FeO 4 spinel oxide.

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“…The obtained Mössbauer spectrum ( Figure S11) reflects the presence of an oxidation product in the form of an associated quadrupole doublet component (  0.21(1) mm/s,   0.32(2) mm/s) with a relative area fraction of  13%, which may arise from Fe 3+ ions situated mainly at the tetrahedral site in a (Fe,Co) 3 O 4 spinel oxide phase [54,55]. Nevertheless, despite the long-time exposure to air,  87% of all iron atoms can still be found in the alloy phase, which confirms the considerable stability of the sample under ambient atmospheric conditions.…”

Section: Resultsmentioning

confidence: 99%

Structure and magnetism of Fe–Co alloy nanoparticles

Klencsár

Németh

Zoltán

et al. 2016

Journal of Alloys and Compounds

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We report the hydrothermal synthesis and structure of Fe x Co 1-x alloy nanoparticles with considerable stability against oxidation under ambient atmosphere. Powder X-ray diffractometry (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma mass spectrometry (ICP-MS), 57 FeMössbauer spectroscopy and magnetization measurements are applied to characterize the composition, morphology, crystal structure, atomic order and magnetic properties of the nanoparticles. As-prepared samples are composed mainly of the bcc Fe x Co 1-x alloy phase.TEM images of heat-treated samples confirm the nanoparticle nature of the original alloys. A consistent analysis of the experimental results leads to x  53% and x  62% Fe atomic ratio respectively in two analogous alloy samples, and suggests that the atomic level structure of the nanoparticles corresponds to that of a fully disordered (A2-type) alloy phase. Exploration of the effect of cobalt on the 57 Fe hyperfine parameters of iron microenvironments suggests that in these alloys the electronic state of Fe atoms is perturbed equally and in an additive manner by atoms in their first two coordination spheres.

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Co57 and Fe57 mössbauer studies of the spinels FeCo2O4 and Fe0.5Co2.5O4

Cited by 32 publications

References 11 publications

First-principles study of the inversion thermodynamics and electronic structure ofFeM2X4(thio)spinels (M=Cr, Mn, Co, Ni;
Santos‐Carballal
¹
,
Roldan
²
,
Grau‐Crespo
³

et al. 2015
Phys. Rev. B

First-principles study of the inversion thermodynamics and electronic structure ofFeM2X4(thio)spinels (M=Cr, Mn, Co, Ni;
Santos‐Carballal
¹
,
Roldan
²
,
Grau‐Crespo
³

et al. 2015
Phys. Rev. B

Structural phase stability and magnetism in Co2FeO4 spinel oxide

Structure and magnetism of Fe–Co alloy nanoparticles

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Co57 and Fe57 mössbauer studies of the spinels FeCo2O4 and Fe0.5Co2.5O4

Cited by 32 publications

References 11 publications

First-principles study of the inversion thermodynamics and electronic structure ofFeM2X4(thio)spinels (M=Cr, Mn, Co, Ni;Santos‐Carballal1, Roldan2, Grau‐Crespo3 et al. 2015Phys. Rev. B

First-principles study of the inversion thermodynamics and electronic structure ofFeM2X4(thio)spinels (M=Cr, Mn, Co, Ni;Santos‐Carballal1, Roldan2, Grau‐Crespo3 et al. 2015Phys. Rev. B

Structural phase stability and magnetism in Co2FeO4 spinel oxide

Structure and magnetism of Fe–Co alloy nanoparticles

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Resources

About

First-principles study of the inversion thermodynamics and electronic structure ofFeM2X4(thio)spinels (M=Cr, Mn, Co, Ni;
Santos‐Carballal
¹
,
Roldan
²
,
Grau‐Crespo
³

et al. 2015
Phys. Rev. B

First-principles study of the inversion thermodynamics and electronic structure ofFeM2X4(thio)spinels (M=Cr, Mn, Co, Ni;
Santos‐Carballal
¹
,
Roldan
²
,
Grau‐Crespo
³

et al. 2015
Phys. Rev. B