Thermolyse von Kalium‐ und Ammoniumpentafluorometallat‐hydraten. Eine in situ‐EPR‐Studie

Lück, R.; Bentrup, Ursula; Stößer, Reinhard

doi:10.1002/zaac.19895760124

Cited by 3 publications

(1 citation statement)

References 9 publications

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“…The structural phase transition clearly indicated by DSC measurements is an important aspect in the complete understanding of the magnetic properties of this compound at low temperature. Additional evidence for the phase transition considered herein comes from the X-band ESR study of (NH 4 ) 2 FeF 5 ·H 2 O by Lück et al . On cooling from ambient to 77 K, they found (for an undiluted sample) a large increase in line width Γ for the intense signal at g ∼ 2.…”

Section: Discussionmentioning

confidence: 52%

Magnetic Properties of (NH₄)₂FeF₅·H₂O: Influence of a Structural Phase Transformation and Relevance of Ambient Temperature Structure Determinations to the Interpretation of Low Temperature Magnetic Behavior

1996

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Low temperature magnetic properties of (NH4)2FeF5·H2O have been investigated via iron-57 Mössbauer spectroscopy and ac susceptibility measurements. The high temperature ac susceptibility data can be fitted to a Curie−Weiss law with C = 4.22 ± 0.05 emu K mol-1 and ϑ = −3.9 ± 0.5 K while the fit of the low temperature data to a Heisenberg linear-chain model yields g = 1.97 ± 0.02 and an intrachain constant J/k B = −0.40 ± 0.02 K. At lower temperatures (NH4)2FeF5·H2O exhibits a crossover to three dimensional magnetic ordering with T c = 2.2 ± 0.05 K and 1.61 ± 0.05 K from Mössbauer spectroscopy and ac susceptibility, respectively. Differential scanning calorimetry measurements suggest a first-order structural phase transition centered at T s = 139 ± 1 K on heating and T s = 125 ± 1 K on cooling for (NH4)2FeF5·H2O. No such transformation is suggested by scanning calorimetry studies of the corresponding K+, Rb+ and Cs+ analogues. The limiting internal hyperfine field, H n(0 K), is 45 T, indicating some 25% zero point spin reduction consistent with significant 1-d magnetic behavior. All the experiments reported here have been performed following varied and careful thermal treatments. A particularly interesting result is the observation of a persistent rapidly relaxing fraction that the Mössbauer spectra of (NH4)2FeF5·H2O clearly exhibit below T c but which is not seen in previous studies of the K+, Rb+, and Cs+ compounds. A probable explanation for this is the loss of magnetic equivalence of the Fe3+ sites as a result of the structural phase transition. This behavior further calls into question the still common practice of interpretation of low temperature magnetic phenomena largely on the basis of ambient temperature structure determinations.

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Section: Discussionmentioning

confidence: 52%

Magnetic Properties of (NH₄)₂FeF₅·H₂O: Influence of a Structural Phase Transformation and Relevance of Ambient Temperature Structure Determinations to the Interpretation of Low Temperature Magnetic Behavior

1996

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ChemInform Abstract: Thermolysis of Potassium and Ammonium Pentafluorometallate Hydrates. An in situ‐EPR Study

1990

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ESR evidence of order/disorder transitions in solids caused by dehydration

Stößer

Scholz

1997

Appl. Magn. Reson.

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ESR spectroscopy was used to study order/disorder phenomena in paramagnetically doped solids. The dehydration process of alurninium fluoride and oxide hydrates and aluminosilicates was examined by ESR in situ measurements as well as using thermoanalytically quenched samples. Two types of amorphous states of solids have been studied: inorganic glasses in the conventional sense and amorphous states of solids which have not passed the liquid state. The complete ESR fine structure pattern of Fe 3 § ions is susceptible with respect to order/disorder processes of the actual host matrix. Dehydration processes bear some model character in this field. A quantitative description of the disorder effects on the Fe 3 § ESR could be given on the basis of a complete spin Hamiltonian using distributions of the fourth order spin coupling parameters.

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Thermolyse von Kalium‐ und Ammoniumpentafluorometallat‐hydraten. Eine in situ‐EPR‐Studie

Cited by 3 publications

References 9 publications

Magnetic Properties of (NH₄)₂FeF₅·H₂O: Influence of a Structural Phase Transformation and Relevance of Ambient Temperature Structure Determinations to the Interpretation of Low Temperature Magnetic Behavior

Magnetic Properties of (NH₄)₂FeF₅·H₂O: Influence of a Structural Phase Transformation and Relevance of Ambient Temperature Structure Determinations to the Interpretation of Low Temperature Magnetic Behavior

ChemInform Abstract: Thermolysis of Potassium and Ammonium Pentafluorometallate Hydrates. An in situ‐EPR Study

ESR evidence of order/disorder transitions in solids caused by dehydration

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Thermolyse von Kalium‐ und Ammoniumpentafluorometallat‐hydraten. Eine in situ‐EPR‐Studie

Cited by 3 publications

References 9 publications

Magnetic Properties of (NH4)2FeF5·H2O: Influence of a Structural Phase Transformation and Relevance of Ambient Temperature Structure Determinations to the Interpretation of Low Temperature Magnetic Behavior

Magnetic Properties of (NH4)2FeF5·H2O: Influence of a Structural Phase Transformation and Relevance of Ambient Temperature Structure Determinations to the Interpretation of Low Temperature Magnetic Behavior

ChemInform Abstract: Thermolysis of Potassium and Ammonium Pentafluorometallate Hydrates. An in situ‐EPR Study

ESR evidence of order/disorder transitions in solids caused by dehydration

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Magnetic Properties of (NH₄)₂FeF₅·H₂O: Influence of a Structural Phase Transformation and Relevance of Ambient Temperature Structure Determinations to the Interpretation of Low Temperature Magnetic Behavior

Magnetic Properties of (NH₄)₂FeF₅·H₂O: Influence of a Structural Phase Transformation and Relevance of Ambient Temperature Structure Determinations to the Interpretation of Low Temperature Magnetic Behavior