epsl, 2004, 229/1-2 pp. 31-43
DESCRIPTION
A new three-axis vibrating sample magnetometer for continuous high-temperature magnetization measurements : Applications to paleo- and archeointensity determinations. Maxime LE GOFF and Yves GALLET. EPSL, 2004, 229/1-2 pp. 31-43. - PowerPoint PPT PresentationTRANSCRIPT
EPSL, 2004, 229/1-2 pp. 31-43.
Maxime LE GOFF and Yves GALLET
A new three-axis vibrating sample magnetometer for continuous high-temperaturemagnetization measurements :
Applications to paleo- and archeointensity determinations
Paleo- and archeointensity studiesare fastidious and often unproductive
due to poor data quality
It is possible to make them fasterby measuring the magnetization
at high temperatures
TRIAXE SENSOR
must take into account the thermal dependence of the spontaneous
magnetization
High-temperature version of the Thellier and Thellier method revised by Coe
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Temperature (°C)
Mto
tal (
10-8
Am
²)
NRM
T1 = 148°C
H = 0
High-Temperature Magnetization Measurements
Heating Troom to T1 (H=0)
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Temperature (°C)
Mto
tal (
10-8
Am
²)
H = 0NRM
T1 = 148°C
T2 = 448°CCurve #1
High-Temperature Magnetization Measurements
Heating T1 to T2 (H=0)
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Temperature (°C)
Mto
tal (
10-8
Am
²)
H = 0NRM
T1 = 148°C
T2 = 448°C
Curve #1
Curve #2
Curve #3
High-Temperature Magnetization Measurements
Cooling to T1 andHeating T1 to T2 (H=0)
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Temperature (°C)
Mto
tal (
10-8
Am
²)
H = 70µT
H = 70 µTNRM
T1 = 148°C
T2 = 448°CCurve #1
Curve #2
Curve #3
High-Temperature Magnetization Measurements
Applying Hlab = 70µT
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Temperature (°C)
Mto
tal (
10-8
Am
²)
NRM
T1 = 148°C
T2 = 448°C
Curve #1
Curve #2
Curve #3
Curve #4
High-Temperature Magnetization Measurements
Cooling T2 to T1 (H = 70µT)
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700
800
900
0 50 100 150 200 250 300 350 400 450 500
Temperature (°C)
Mto
tal (
10-8
Am
²)
H = 0NRM
T1 = 148°C
T2 = 448°C
Curve #1
Curve #2
Curve #3
Curve #4
High-Temperature Magnetization Measurements
Hlab = 0µT
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900
0 50 100 150 200 250 300 350 400 450 500
Temperature (°C)
Mto
tal (
10-8
Am
²)
NRM
T1 = 148°C
T2 = 448°C
Curve #1
Curve #2
Curve #3
Curve #4Curve #5
High-Temperature Magnetization Measurements
Heating T1 to T2 (H=0)
R(Ti) = Hlab * 1(Ti) / 5(Ti)
R’(Ti) = Hlab * 1’(Ti) / 5’(Ti)
Remaining NRM (1) and TRM (5) fractions between Ti and T2
R ratio
Lost NRM (1’) and TRM (5’) fractions between T1 and Ti
R’ ratio
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TiT1 = 150°C
T2 = 450°C
Two possibilities to derive intensity data
NRM
TRM
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Temperature (°C)
R, R
' (µT
)
R
R'
Test on a pseudo NRM acquired in a field of 50µT in the same conditions as the laboratory TRM (Hlab=50 µT)
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R
R'
Ancient NRM : R increasing, R’ much more constant
Ti, (°C)
R, R’ (µT)
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Temperature (°C)
R, R
' (µT
)
NRM 0.5°/mn; TRM 25°/mn
NRM 0.5°/mn, TRM 6°/mn
NRM 0.5°/mn, TRM 2°/mn
Cooling rate effect
R’ must be considered
Correction for the TRM anisotropy
Comparison between archeointensity
data obtained from the Thellier and
Thellier method revised by Coe and
from the Triaxe
(Samples from Mesopotamia previously studied by Genevey et al., JGR, 2003)
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R
R'
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Selection criteria
• A large NRM fraction must be involved
• Expected behaviour of R and R’ curves
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Temperature (°C)
R
R'
Example of rejected sample
MR 15
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Temperature (°C)
R' (
µT)
Archeointensity results from a site of baked bricks from Mesopotamia (Mari, Syria)
6 samples
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-4000 -3000 -2000 -1000 0
Thellier Thellier - CoeTriaxe Same SiteTriaxe New Site
Comparison between archeointensity results obtained from the Thellier and Thellier and Triaxe methods
H (µT)
Age (BC)
CONCLUSIONS
• The experimental procedure was successfully tested with archeological baked materials. We need now to work on volcanic samples.
• Other applications of the Triaxe :- Viscosity at high temperature.- Alteration.- Coupling between different magnetic phases.- etc.
