Ferromagnetic-Paramagnetic Transition in Iron

Arajs, Sigurds; Colvin, R. V.

doi:10.1063/1.1702873

Cited by 83 publications

(28 citation statements)

References 10 publications

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“…Thorpe and Senfile [1964] have suggested that X• in splash-form tektites may be due to the presence of submicroscopic spherules in the glass. For a small ferromagnetic spherical particle the demagnetizing field is equal and opposite to the applied dc field, and therefore spherical iron or magnetite particles appear to be paramagnetic at low dc magnetic fields [see Arajs and Colvin, 1964]. Alternatively, the same spherules will be ferromagnetic at high magnetic fields (above saturation).…”

Section: Experimental Measurements and Resultsmentioning

confidence: 99%

Magnetic measurements of glass from Tikal, Guatemala: Possible tektites

Senftle¹,

Thorpe²,

Grant³

et al. 2000

J. Geophys. Res.

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Abstract. Certain glass nodules found at the archeological site at Tikal, Guatemala, have been considered as possible tektites. To test this possibility, magnetic studies have been made on three of the glass specimens. These specimens are similar to tektites, both visually and also because they contain very little Fe 3+ as detected by M6ssbauer spectroscopy. The magnetic Curie constants are similar in magnitude to those found for normal tektites but show some variation from point to point in the same specimen. This variation reflects an inhomogeneity in the iron concentration. The Fe 2+ calculated from the Curie constants accounts for most of the iron. The temperature-independent component of the total dc magnetic susceptibility is several times higher than that found in tektites from other strewn fields. The high values can be explained if the glass contains metallic iron spherules with Fe in the parts per million range and/or a ferromagnetic component which does not saturate in a low magnetic field. The magnetic properties resemble those of Muong Nong type tektites and suggest that the Tikal glass specimens are tektites of the Muong Nong type. IntroductionEsserie et al. [1987] have reported microprobe analyses of 11 unworked nodules of olive-green vesicular glass found in the Mayan city of Tikal, Guatemala. Their analysis indicated that the glass had an andesitic composition. They suggested that because of the complete lack of crystallites these specimens would be highly anomalous if they were andesitic obsidians. Because it is unlikely, and surely unique, that these specimens were derived from andesitic obsidian, Esserie et al. [1987] further suggested that the specimens may be impactites from a terrestrial andesitic source rock. Later, Moholy-Nagy and Nelson [1990] reported on a study of some 30 obsidian artifacts from the same area. In an effort to trace the source of the obsidian they analyzed the specimens for 10 different elements using X-ray fluorescence. One of the specimens (their number 1589) was an unworked brownish-green glass nodule that had a composition distinctly different from the other obsidian artifacts. The Fe, Ti, and Sr concentrations were higher, and the Rb and Nb concentrations were lower than those determined for any of the other obsidian fragments. The obsidian fragments could all be related to known local quarries, while specimen 1589 was of unknown origin and from a source of more andesitic composition. The surface of the nodule was pitted, and the glass was remarkably free of crystallites. Because of these characteristics it was suggested that this specimen might We report here a magnetic study on three of the specimens described in the above studies and designated as 12T-451/79, 20M-97B/41 (same as Moholy-Nagy and Nelson [1990] specimen 1589), and 24F-26/11 (hereinafter referred to as 12T, 20M, and 24F) in an attempt to confirm them as true tektites. Senfile and Thorpe [1959] have shown that magnetic properties can be used to distinguish tektites from obsidian glass. Obsidians ...

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Section: Experimental Measurements and Resultsmentioning

confidence: 99%

Magnetic measurements of glass from Tikal, Guatemala: Possible tektites

Senftle¹,

Thorpe²,

Grant³

et al. 2000

J. Geophys. Res.

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“…Because the paramagnetic susceptibility of ferrite satisfies the Curie-Weiss law only above 1150 K, the paramagnetic H ϭ 1.82 B derived from the Curie constant cannot be used for ferrite in most temperature ranges and it may be more reasonable to use the ferromagnetic H . [9] A mapping of the magnetization-magnetic field-temperature diagram (M-H-T) surface is calculated and is shown in Figure 4. This curve corresponds to the shape of an experimental curve, such as that reported by Gorodestsky et al [10] for the weak ferromagnet YFeO 3 .…”

Section: A Calculation Of the Phase Transformation Temperature Changmentioning

confidence: 99%

“…These are fitted as functions of temperature at the magnetic fields of 100, 200, 300, 400, and 500 kOe, and are described by Eqs. [8], [9], [10], [11], and [12], respectively. at T Ͻ 1043 K and H ϭ 100 kOe at T Ͼ 1043 K and H ϭ 100 kOe [8] at T Ͻ 1043 K and H ϭ 200 kOe at T Ͼ 1043 K and H ϭ 200 kOe [9] at T Ͻ 1043 K and H ϭ 300 kOe at T Ͼ 1043 K and H ϭ 300 kOe [10] at T Ͻ 1043 K and H ϭ 400 kOe at T Ͼ 1043 K and H ϭ 400 kOe [11] at T Ͻ 1043 K and H ϭ 500 kOe at T Ͼ 1043 K and H ϭ 500 kOe [12] ⌬G M a (T) ϭ Ϫ39.…”

Section: Gibbs Free Energy Change By Magnetic Fieldmentioning

confidence: 99%

“…[8], [9], [10], [11], and [12], respectively. at T Ͻ 1043 K and H ϭ 100 kOe at T Ͼ 1043 K and H ϭ 100 kOe [8] at T Ͻ 1043 K and H ϭ 200 kOe at T Ͼ 1043 K and H ϭ 200 kOe [9] at T Ͻ 1043 K and H ϭ 300 kOe at T Ͼ 1043 K and H ϭ 300 kOe [10] at T Ͻ 1043 K and H ϭ 400 kOe at T Ͼ 1043 K and H ϭ 400 kOe [11] at T Ͻ 1043 K and H ϭ 500 kOe at T Ͼ 1043 K and H ϭ 500 kOe [12] ⌬G M a (T) ϭ Ϫ39. 15 Equation [7] may also be applied to the magnetic Gibbs free energy change of austenite because the Neel temperature of austenite is very low.…”

Section: Gibbs Free Energy Change By Magnetic Fieldmentioning

confidence: 99%

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An effect of a strong magnetic field on the phase transformation in plain carbon steels

Joo

Kim

Koo

et al. 2004

Metall Mater Trans A

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The effect of a magnetic field on the Gibbs free energy of a material depends on its magnetization behaviors. To investigate the change in the Fe-Fe 3 C phase diagram caused by a high external magnetic field, the magnetic Gibbs free energies of the phases such as austenite, ferrite, and cementite are calculated on the basis of the molecular field theory. Using the calculated Gibbs free energy as a function of weight percent carbon and temperature at a particular magnetic field, a phase diagram of the Fe-Fe 3 C system is drawn. The phase diagram is shifted upward so that the Ac 1 and Ac 3 temperatures increase as the magnetic field is applied, but the Ac m temperature change is almost independent of applied magnetic field value. The increase of eutectoid temperature and composition and its application to microstructural control are discussed.

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“…Hao and Ohtsuka [12] reported a value 0.8 • C T −1 for the phase boundary between bcc and fcc of pure Fe in the paramagnetic state when the applied filed is low ( 10 T). In this report, the paramagnetic susceptibility data of pure Fe in its bcc and fcc structures [21][22][23][24][25][26][27] is first re-evaluated. The new susceptibility values as a function of temperature are then used to calculate the Gibbs energy change due to applied magnetic fields based upon the Curie-Weiss law.…”

Section: Introductionmentioning

confidence: 99%

On Hartogs Compacts of Holomorphy

Širinbekov¹

1982

Math. USSR Sb.

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The CALPHAD (calculations of phase diagrams) method is used to examine the effects of applied magnetic fields on the α/γ phase boundary in the Fe-Si system in the paramagnetic state. The reported susceptibility data for pure Fe is first re-evaluated. The contributions to the total Gibbs energy of the ferrite (α) and austenite (γ ) from the external fields are calculated based on the Curie-Weiss law and the re-evaluated susceptibility data. The Fe-Si phase diagram on the Fe-rich side as a function of applied field is calculated using the Thermo-Calc ™ package. With increasing field strength, the γ loop shrinks monotonically; that is, the α/γ -Fe transition temperature increases while that for γ /δ-Fe transition decreases, albeit more slowly. Finally, in conformance with the existing CALPHAD databank, Redlich-Kister polynomials are proposed to account for the compositional and temperature dependence of the contribution to the total Gibbs energy from the applied field in the paramagnetic state in the range over which the Curie-Weiss law is obeyed.

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Ferromagnetic-Paramagnetic Transition in Iron

Cited by 83 publications

References 10 publications

Magnetic measurements of glass from Tikal, Guatemala: Possible tektites

Magnetic measurements of glass from Tikal, Guatemala: Possible tektites

An effect of a strong magnetic field on the phase transformation in plain carbon steels

On Hartogs Compacts of Holomorphy

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