High-temperature characteristics of a natural titanomagnetite

Hartstra, R. L.

doi:10.1111/j.1365-246x.1982.tb05997.x

Cited by 22 publications

(20 citation statements)

References 12 publications

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“…The observed SD features for small grains of DKA may be a reflection of such a high SD to pseudo-single domain (PSD) transition for this titanomagnetite. However, in DKA submicroscopic Fe-rich inclusions were observed (Hartstra 1982). At laboratory temperature these inclusions are magnetically screened and therefore should not influence the isothermal processes which we are dealing with here.…”

Section: R L Haftsrramentioning

confidence: 90%

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Grain-size dependence of initial susceptibility and saturation magnetization-related parameters of four natural magnetites in the PSD--MD range

Hartstra¹

1982

Geophysical Journal International

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Initial susceptibility, coercive force and several types of remanent coercive forces were measured on a set of artificial rock specimens containing grain-size fractions of a natural magnetite and titanomagnetite, both of which are optically homogeneous and a natural titanomagnetite and titanomaghemite, both of which show exsolution phenomena. It was found subsequently that the optically homogeneous titanomagnetite contains some submicroscopic Fe-rich inclusions. These inclusions are magnetically screened in coarse grains; only for the lower grain sizes studied they have an appreciable influence on the data. The size of the fractions varied from < 5 to 250pm. The parameters and several parameter ratios are plotted as a function of grain size. Several of these parameters can be used as mineralogical and grain-size indicators. The varying degree of exsolution of the minerals is reflected in the gradients of the plots. From plots of initial susceptibility versus grain size it is concluded that the shape of the grains does not play a dominant role in determining the change of this parameter with grain size. Variation of the various parameters with grain size is explained in terms of a gradual transition from large PSD grains to MD grains without there being any sharp transition. For titanomagnetite ( x = 0.55) the transition takes place at grain sizes that are about 15 pm larger than for magnetite.

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Section: R L Haftsrramentioning

confidence: 90%

“…However, during later experiments involving thermal demagnetization techniques, it was found that this titanomagnetite contains submicroscopic Fe-rich inclusions that are smaller than 0.020 pm (Hartstra 1982). Probably we are dealing here with an early stage of exsolution.…”

Section: W Y 2 I )mentioning

confidence: 95%

Grain-size dependence of initial susceptibility and saturation magnetization-related parameters of four natural magnetites in the PSD--MD range

Hartstra¹

1982

Geophysical Journal International

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“…In the case of a natural titanomagnetite, which was in an early stage of exsolution, it was found that normalized continuous thermal decay curves for Z , , and ARM were identical, whereas those for TRM were of a completely different shape (Hartstra 1982a).…”

Section: Introductionmentioning

confidence: 97%

“…In the present study alternating field demagnetization curves for ARM induced in artificial rock specimens were studied as a function of PSD/MD grain size and were compared with alternating field demagnetization curves for Z , , induced in identical specimens (Hartstra, 1982a). Furthermore, continuous recordings of low-temperature cycles to liquid-nitrogen temperature applied to ARM and I,, which were induced in the artificial specimens are presented for various grain sizes.…”

Section: Introductionmentioning

confidence: 97%

A comparative study of the ARM and Isr of some natural magnetites of MD and PSD grain size

Hartstra¹

1982

Geophysical Journal International

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ARM and I, stability with respect to alternating field and lowtemperature treatment were measured for a set of artificial rock specimens. Each of the specimens contained a known amount of a natural magnetic mineral of a known grain size. The following minerals were used: a homogeneous natural magnetite, a natural titanomagnetite with submicroscopic Fe-rich inclusions, and a natural titanomagnetite and a natural titanomaghemite that both show exsolution phenomena. The grain size of the fractions varied from < 5 to 250pm. It is found that the stability of ARM and Z , of multi-domain grains with respect to alternating fields and low-temperature treatment is similar, whereas for the smallest grains studied (< 5 pm) ARM is more stable than I,. Multi-domain ARM data from this study are in agreement with current multi-domain ARM theory. Low-temperature behaviour of ARM and I,, can be explained either in terms of a model in which stable moments in the bulk of the grains are screened by the surrounding matrix or in terms of a model in which regeneration of the bulk remanence plays a role and in which stable moments are situated on the surfaces of the grains.

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“…It is commonly observed (e.g., HARTSTRA, 1982) that when a sample (which shows a peak in the continuous thermal demagnetization curve) with a remanence is cooled in zero field from or near the peak temperature, the remanence decreases and becomes nearly zero, and then increases again (Fig. 9).…”

Section: S Psd Momentmentioning

confidence: 94%

Measurement of magnetization at high temperatures and the origin of thermoremanent magnetization. A review.

Sugiura

1989

J. geomagn. geoelec

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Recent studies on the measurements of magnetization at high temperatures are reviewed. Use of a second gradient magnetometer is the main advance in instrumentation. Direct observation of how remanent magnetization is acquired and/ or lost by changing temperature provides strong evidence about the origin of thermoremanent magnetization. According to such observation, Neel's single domain theory seems to be correct. Neel's multi domain theory (which is originally a two domain theory, but is frequently applied to grains with many domains), however, cannot explain the behavior of magnetization at high temperatures. The behavior of magnetization in pseudo single domain (psd) grains is strongly dependent on the grain size. It seems that the heterogeneity in the magnetic grains and the screening effect are the main effects which characterize the psd moment.It should be emphasized that at high temperatures, there are still many interesting phenomena which have not been adequately described and/ or explained. Some of these interesting phenomena are shown as a guide for future studies.The high temperature measurement of magnetization is undoubtedly important for understanding TRM (thermoremanentrnagnetization), because TRM is acquired at high temperatures. In the 1950's and 1960's, when astatic magnetometers were the main instruments for the measurements of magnetization, there were many studies which reported measurements of magnetization at high temperatures and important advancements were made (e.g., NAGATA and OZIMA, 1955). In the 1970's and early 1980's, however, relatively few such studies were done. This is probably because of the difficulty in using spinner magnetometers and SQUID magnetometers at high temperatures (COLLINSON, 1983). Although some spinner magnetometers can be used at high temperatures, it is difficult to control the atmosphere, and induced magnetization cannot be measured. For rock magnetic purposes, it is important to control the atmosphere so that the magnetic grains are not altered during high temperature measurements. SQUID magnetometers of ordinary design cannot be used with electronic furnaces (CoLLINSON,1983). Such disadvantage has prevented the use of these modern instruments for high temperature measurements. Recently, however, second gradient SQUID magnetometers were put to use for high

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High-temperature characteristics of a natural titanomagnetite

Cited by 22 publications

References 12 publications

Grain-size dependence of initial susceptibility and saturation magnetization-related parameters of four natural magnetites in the PSD--MD range

Grain-size dependence of initial susceptibility and saturation magnetization-related parameters of four natural magnetites in the PSD--MD range

A comparative study of the ARM and Isr of some natural magnetites of MD and PSD grain size

Measurement of magnetization at high temperatures and the origin of thermoremanent magnetization. A review.

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