Theoretical analysis of thermomagnetic properties, low-temperature hysteresis and domain structure of titanomagnetites

Clark, David; Schmidt, P. W.

doi:10.1016/0031-9201(82)90029-2

Cited by 35 publications

(16 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[23] When heated in argon, the samples show a gradual increase of k with a well-pronounced Hopkinson peak, followed by a sharp decrease of k to the Curie temperature ( Figure 3a). Such a behavior is characteristic for small pseudo single domain (PSD) and single-domain (SD) magnetite grains [Dunlop, 1974;Clark and Schmidt, 1982]. On cooling, the Hopkinson peak disappears and a small bump is observed at lower (400 -500°C) temperatures ( Figure 3a).…”

Section: Thermomagnetic Analysismentioning

confidence: 98%

Thermochemical remanent magnetization in Precambrian rocks: Are we sure the geomagnetic field was weak?

Смирнов

Tarduno

2005

J. Geophys. Res.

View full text Add to dashboard Cite

[1] Thellier paleointensity determinations from two dikes of the Early Proterozoic ($2.46 Ga) Matachewan dike swarm (Canada) yield field values of 2.14 ± 0.18 and 9.81 ± 1.65 mT. Corresponding values of virtual axial dipole moment are very low (0.54 ± 0.05 Â 10 22 and 2.49 ± 0.42 Â 10 22 Am 2 , respectively) when compared with the modern field. The characteristic remanent magnetization (ChRM) was isolated over a narrow range of high unblocking temperatures ($520-580°C). Detailed rock magnetic analyses indicate that the ChRM is carried by nearly stoichiometric pseudo single domain magnetite. Scanning electron microscopy (SEM) reveals that the magnetite is in the form of fine intergrowths with ilmenite, formed by oxyexsolution during cooling. The high-temperature oxidation defined in the SEM images could have continued at temperatures below the Curie point of magnetite. In this case, the ChRM would be a thermochemical remanent magnetization (TCRM) rather than a thermal remanent magnetization (TRM). Estimates of the TCRM/TRM ratio show that the Thellier data could underestimate the true field value by a factor of 4 without violating experimental selection criteria. This uncertainty in TRM fidelity translates into a potential range of field values that spans that defined by the modern field ($8 Â 10 22 Am 2 ) and proposed low Precambrian levels ($2 Â 10 22 Am 2 ). Therefore understanding further how TCRM is acquired and records the field represents a major challenge if these and many other similar rocks are to be used in Thellier studies aimed at defining the strength of the Precambrian field.Citation: Smirnov, A. V., and J. A. Tarduno (2005), Thermochemical remanent magnetization in Precambrian rocks: Are we sure the geomagnetic field was weak?,

show abstract

Section: Thermomagnetic Analysismentioning

confidence: 98%

Thermochemical remanent magnetization in Precambrian rocks: Are we sure the geomagnetic field was weak?

Смирнов

Tarduno

2005

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…The Hopkinson peak in the plagioclase κ( T ) curve with a sharp descent just below 580°C (Figure 1a) is characteristic of SD magnetite [ Dunlop , 1974; Radhakrishnamurty et al , 1981; Clark and Schmidt , 1982]. A possible second peak with a descent around 675°C, the Curie point of hematite, is not seen in the cooling curve and is probably noise.…”

Section: Magnetic Properties Characterizationmentioning

confidence: 99%

“…A possible second peak with a descent around 675°C, the Curie point of hematite, is not seen in the cooling curve and is probably noise. In the heating curve of the dark minerals, κ is independent of T (Figure 1b), a hallmark of large MD grains where κ is governed by self‐demagnetization [ Dunlop , 1974; Deutsch et al , 1981; Radhakrishnamurty et al , 1981; Clark and Schmidt , 1982; Soffel et al , 1982]. The only magnetic mineral is magnetite.…”

Section: Magnetic Properties Characterizationmentioning

confidence: 99%

Linear and nonlinear Thellier paleointensity behavior of natural minerals

2005

View full text Add to dashboard Cite

We tested single‐domain (SD) and multidomain (MD) theories of the acquisition and thermal demagnetization of thermoremanent magnetization (TRM) and partial TRM (pTRM) in Thellier paleointensity determination, using as samples plagioclase and mafic minerals extracted from Matachewan diabase dikes. Susceptibility, hysteresis, and coercivity data indicate that the plagioclase contains mainly SD grains of magnetite while the mafic minerals (clinopyroxene, biotite, and actinolite) contain mainly MD magnetite. The extracted minerals were used in simulated Thellier experiments with laboratory TRM as a proxy for natural remanent magnetization (NRM). The plagioclase behaved ideally, as predicted by Néel SD theory, giving a linear NRM‐pTRM (Arai) plot with positive pTRM checks. The mafic minerals behaved nonideally, with strongly curved Arai plots sagging below the ideal SD line, in accord with observations for MD magnetites and with predictions that in heating to moderate temperatures T, more TRM is lost than can be regained as pTRM, causing convex‐down Arai plots. In experiments with pTRM parallel to NRM, all pTRM tail checks were zero, but pTRM checks increasingly deviated from the Arai curve toward the SD line as T increased. However, in repeat Thellier experiments, pTRMs at all T agreed with the original pTRMs. The negative pTRM checks were therefore not due to physicochemical alteration but rather to departure from initial states with different magnetic histories than those of the original pTRMs. The inability of pTRM checks to reliably distinguish between MD behavior and irreversible alteration could lead to overestimates of paleointensity from straight‐line fits to the low‐T “unaltered” part of the Arai curve or underestimates from fits to high‐T data. Alternating field cleaning to 15 mT before each Thellier step made the Arai plot only marginally less curved. Low‐temperature demagnetization (LTD, zero‐field cycling through the 120 K Verwey transition) hardly changed the curvature of the Arai plot for pTRM parallel to NRM. For pTRM perpendicular to NRM, LTD led to an inflected Arai curve straddling the ideal SD line. Data of either form would not give reliable paleointensity values. No presently available pretreatment renders the paleointensity data of MD grains usable. SD and nearly SD grains which behave ideally in the Thellier experiment remain the only useful recorders of absolute paleointensity.

show abstract

“…TM10 is known to show the isotropic point slightly below 100 K (Syono, 1965). Based on this result, Clark and Schmidt (1982) have theoretically predicted that multidomain TM10 should exhibit a peak in susceptibility around this temperature. Moskowitz et al (1998) has reported SIRM(T) and χ (T ) curves for a suite of synthetic single crystal titanomagnetites in the composition range from TM0 to TM60.…”

Section: The Verwey Transitionmentioning

confidence: 99%

Magnetic properties of subaerial basalts at low temperatures

Kosterov

2014

Earth Planet Sp

View full text Add to dashboard Cite

Magnetic properties have been measured as a function of temperature from 2 K to room temperature for twentyone samples of subaerial basalts of different origin and age, using an MPMS instrument. In all samples but four, titanomagnetite with a titanium content of less than 5 per cent has been determined as a dominant magnetic mineral carrying NRM from χ(T ) measurements above room temperature and Verwey transition observations. However, the new low-temperature experiments yielded evidence of the presence of another magnetic mineral in all samples. This mineral accounts for up to 70 per cent of saturation magnetization at 2 K and acquires a relatively strong but thermally unstable SIRM at this temperature. Comparison of susceptibility vs. temperature curves measured in low and high DC biasing fields reveals evidence of superparamagnetic behavior, peaks marking the effective blocking temperatures being shifted from <2 K to about 16 K by a 4.8 T DC magnetic field. At the same time, the presence of peaks in the high-field susceptibility curves indicate that the corresponding magnetic phase does not reach saturation, even in the highest field available to us. A possible candidate to account for these properties is a hemoilmenite with 8-10 mole per cent of hematite, originating from high-temperature deuteric oxidation. This is in accordance with the prevailing occurrence of exsolution lamellae within titanomagnetite grains observed in scanning electron microscopy (SEM) images.

show abstract

Theoretical analysis of thermomagnetic properties, low-temperature hysteresis and domain structure of titanomagnetites

Cited by 35 publications

References 36 publications

Thermochemical remanent magnetization in Precambrian rocks: Are we sure the geomagnetic field was weak?

Thermochemical remanent magnetization in Precambrian rocks: Are we sure the geomagnetic field was weak?

Linear and nonlinear Thellier paleointensity behavior of natural minerals

Magnetic properties of subaerial basalts at low temperatures

Contact Info

Product

Resources

About