Electron delocalization and magnetic behavior in a single crystal of ilvaite, a mixed valence iron silicate

Ghosh, D.; Kundu, Tapanendu; Dasgupta, S.; Ghose, Subrata

doi:10.1007/bf00308218

Cited by 13 publications

(10 citation statements)

References 21 publications

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“…Other than in the "classic" cases of binary oxides showing electron order-disorder transitions (Fe304, Ti407) no discontinuity can be observed in d.c.-conductivity measurements (Coey et al 1984) or single crystal magnetic susceptibility measurements (Ghosh et al 1987) near the relevant transition temperature of approximately 335 K.…”

Section: Pnam) To Monoclinic Phase Transition (T~335 K P21/a)mentioning

confidence: 95%

Polarized single crystal absorption spectroscopy of the Pnam-P2 1/a transition of Ilvaite Ca(Fe2+, Fe3+)Fe2+Si2O8(OH) as measured between 300 K and 450 K

1989

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Abstract. The temperature dependence of the absorption spectra of ilvaite, Ca(FeZ+,Fe3+)FeZ+Si2Os(OH), shows strongly one dimensional transport behaviour with no singularity at the Pnam-P21/a phase transition point near 335 K. Polarized single crystal transmission measurements were carried out between 300 K and 450 K in a frequency range between 600 and 23 000 cm-1. No Drude -absorption at low energies was found at any temperature. A macroscopic, thermodynamic model based on Landau-Ginzburg theory is given which accounts for the observed macroscopic properties of the structural phase transition and its coupling with the Fe 2 +-Fe 3 + ordering. This ordering scheme is discussed on an atomistic level and compared with the behaviour of magnetite and trans-(CH)~.

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Section: Pnam) To Monoclinic Phase Transition (T~335 K P21/a)mentioning

confidence: 95%

Polarized single crystal absorption spectroscopy of the Pnam-P2 1/a transition of Ilvaite Ca(Fe2+, Fe3+)Fe2+Si2O8(OH) as measured between 300 K and 450 K

1989

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“…It is relevant to mention here that we had observed a slow increase in the internal energy in the DTA curve around 340 K (Ghosh et al 1987) shown in insert c of Fig. 1, as also detected by Robie et al (1988).…”

Section: Resultsmentioning

confidence: 54%

“…The set of parameters obtained from best fitting of K• Kit and AK values above 123_+0.5 K (i.e., the transition temperature, Ghosh et al 1987) have been shown in Table 1. The eigenvalues and eigenfunctions corresponding to these set of parameters have also been shown therein.…”

Section: Resultsmentioning

confidence: 99%

“…The present work is a continuation of our earlier work (Ghosh et al 1987) on the study of the thermal characteristic of the magnetic susceptibilities and their anisotropies in different crystallographic planes of a single crystal of ilvaite from Elba (Italy) in the temperature range of 400-21 K. The molar susceptibility Krr in the ab plane was found to rotate on cooling below 343 + 1 K till 90 + 2 K, the crystal being paramagnetic at these temperatures, and the symmetry of the magnetic ellipsoid was found to remain unchanged. The sign of magnetic anisotropy AK=(KII-K• was found to be negative which essentially suggested a singlet ground state 5.4 for the Fe 2+ ions in agreement with previous M6ssbauer studies (Coey et al 1984).…”

Section: Introductionmentioning

confidence: 92%

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Ligand field analysis of the magnetic susceptibilities and M�ssbauer spectra of ilvaite, a mixed valence iron mineral

Kundu

Ghosh

1990

Phys Chem Minerals

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Abstract, The thermal characteristics of magnetic susceptibilities and their anisotropies of single crystal of ilvaite, a mixed valence iron sorosilicate, have been analysed in the light of Ligand Field (LF) theory using a minimum number of approximations. The electronic energy pattern and the corresponding wavefunctions were obtained from best fitting of these experimental results with the corresponding theoretical values. These results were next used to calculate the thermal characteristic of the quadrupole splitting A EQ in ilvaite. It was found that the values of A E e are reasonably close to those reported from M6ssbauer studies. The present analysis suggest appreciable molecular overlap between the orbits of the ligand electrons and those of the Fe 2+ atoms, the overlap being prominent along the chain direction as also observed from electrical conductivity measurements.Burns 1970) and making a minimum number of approximations.It may be mentioned that in LF theory, the basic 3 d orbitals of the Crystal Field theory are modified to include overlap of the electron charge clouds of the ligands with those of the central ion as in Molecular Orbital (MO) theory. LF theory is therefore capable of describing bond polarities from total covalency to total ionic by considering appropriate reduction factors, which occur during calculation of matrix elements for the orbital angular momentum operators and spin angular momentum operators. Thus the expressions for the susceptibilities KII and Kl and the quadrupolar splitting of the Fe z+ are derived in terms of the LF parameters, which are to be determined from best fitting of the experimental results.

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“…Below T~, the symmetry is monoclinic (space group P21/a), where the mirror plane normal to the c axis is lost and the 8(d) sites split up into two 4(e) sites, A0 and Am, which principally contain Fe 2 § and Fe 3+ ions respectively. In addition, ilvaite shows two magnetic phase transitions at about 120 and 40K (Coey et al 1984;Ghosh et al 1987). The electron delocalization between the Fe z+ and Fe 3 + ions in the octahedral A sites has been extensively * Present address: Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou Province, People's Republic of China studied by M6ssbauer spectroscopy in the temperature range 300-520K (Gerard and Grandjean 1971;Grandjean and Gerard 1975;Heilmann et ai.…”

Section: Introductionmentioning

confidence: 99%

Phase transitions in ilvaite, a mixed-valence iron silicate I. A 57Fe M�ssbauer study of magnetic order and spin frustration

1988

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Abstract. llvaite, Ca (Fe 2 +,Fe 3 +)Fez + Si208(OH) shows two magnetic phase transitions, which have been studied by M6ssbauer spectroscopy within the temperature range 120-4 K. The continued charge localization between Fe 2+ and Fe 3 + ions in octahedral A-sites causes the Fe 2 + -Fe 3 + interaction to be ferromagnetic, although the overall magnetic order is antiferromagnetic. The thermal evolution of the hyperfine fields at the Fe 2 § (A) and Fe 3 + (A) sites indicates Bhf: 328 and 523 kOe respectively at 0 K and TN1 = 116K. The corresponding values for Fe z + (B) site are: Bhf 186 kOe and TN2 = 36K. An additional hyperfine field exists at the Fe 2+ (B) site within the temperature range 116-36K due to short-range order induced by the spin ordering in A sites. The considerable difference between the two magnetic transition temperatures is due to spin frustration, because the Fe z + (B) site occurs on a corner common between two triangles with respect to two sets of Fe z+ (A) and Fe 3 + (A) sites with opposite spin directions.

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Electron delocalization and magnetic behavior in a single crystal of ilvaite, a mixed valence iron silicate

Cited by 13 publications

References 21 publications

Polarized single crystal absorption spectroscopy of the Pnam-P2 1/a transition of Ilvaite Ca(Fe2+, Fe3+)Fe2+Si2O8(OH) as measured between 300 K and 450 K

Polarized single crystal absorption spectroscopy of the Pnam-P2 1/a transition of Ilvaite Ca(Fe2+, Fe3+)Fe2+Si2O8(OH) as measured between 300 K and 450 K

Ligand field analysis of the magnetic susceptibilities and M�ssbauer spectra of ilvaite, a mixed valence iron mineral

Phase transitions in ilvaite, a mixed-valence iron silicate I. A 57Fe M�ssbauer study of magnetic order and spin frustration

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