1. Ferromagnetic Resonance ofFerromagnetic Resonance of
Precipitated Phases in LunarPrecipitated Phases in Lunar
GlassesGlasses
David L. GriscomDavid L. Griscom
impact Glass research internationalimpact Glass research international
Lote 454 Ranchitos, San Carlos, Sonora, MexicoLote 454 Ranchitos, San Carlos, Sonora, Mexico
Mail to: 3938 E Grant Rd #131, Tucson, AZ 85712Mail to: 3938 E Grant Rd #131, Tucson, AZ 85712
PresentationPresentation àà L’INSTNL’INSTN au Centre des Etudes Nucléaires de Saclay,au Centre des Etudes Nucléaires de Saclay,
3. Mare Imbrium Seen from the Apollo 15 Lunar ModuleMare Imbrium Seen from the Apollo 15 Lunar Module
Apennine Mountains
Hadley Rill
Apollo 15 landing site
4. On the Moon with Apollo 15: View Across Hadley RillOn the Moon with Apollo 15: View Across Hadley Rill
Apennine Mountain Front
Mare Surface
Far side of Hadley Rill
Lunar Soil
Basalt Flow !
5. Morphologies of Lunar-Soil GlassesMorphologies of Lunar-Soil Glasses
The lunar soil (regolith) typically comprises up to 50% glass – mostly due to impacts
Glassy
Agglutinates
Splash forms
6. Transmission Electron Micrograph of a TypicalTransmission Electron Micrograph of a Typical
Lunar-Soil Glassy AgglutinateLunar-Soil Glassy Agglutinate
From: R.M. Housley, R.W. Grant, and N.E. Patton, Proc. Lunar Sci. Conf. 4th
(1973) 2737.
they are spherical – assuring
that the FMR spectrum is
governed by magnetocrystalline
anisotropy.
they are smaller than ~200 Å –
guaranteeing that they have no
more than one magnetic
domain and…
These particles are ideal for
ferromagnetic resonance
(FMR) investigations
because...
7. • Source of microwaves
οf frequency ν. MICROWAVE SOURCE
θ
DETECTOR,
AMPLIFIER
SAMPLE
X AXIS
Y AXIS
Absorption
Magnetic Field
FIELD PROBE
ELECTROMAGNET
POLE FACES
CHART RECORDER
θ=0 θ=90
• The microwaves are
absorbed by unpaired
electrons in the sample
when hν = gβH + A, where
h is Planck’s constant,
β is the Bohr magneton, and
A represents one of many
possible interactions with
atoms in the crystal lattice.
• g and the parameters of A (which generally
display angular dependencies) comprise the
measurable parameters.
• The sample is placed
between the pole faces
of an electromagnet
producing a variable
magnetic field, H.
The Experimental MethodThe Experimental Method
8. The “Characteristic” Resonance of Lunar SoilsThe “Characteristic” Resonance of Lunar Soils
Adapted from: R.A. Weeks et al. (1970) Science 167, 704.
…was determined to be a ferromagnetic resonance by F.-D. Tsai
9. Ferromagnetic Resonance ofFerromagnetic Resonance of SphericalSpherical,, Single-DomainSingle-Domain
Single Crystals of Cubic StructureSingle Crystals of Cubic Structure
Angle of applied magnetic
field, H, relative to the
crystallographic axes
Field position of resonance
line as function of angle
FMR spectrum
averaged over
all angles
Measured parameters include the g value and magnetocrystalline anisotropy
constant, K1.
H MagnitudeofH→
(Ha = K1/Ms, where Ms is the saturation magnetization.)
K1
10. Powder
Patterns
Simulated
Spectra
Spectrum of Pure α Iron Precipitated in Silica
Glass and Fitted Simulation Using Literature
Values for g Value and Magnetocrystalline
Anisotropy Constants, K1, K2, and K3.
D.L. Griscom (1981) J. Magn. Res. 45, 81-87.
FMR Spectrum of Single-Domain Spherical Particles ofFMR Spectrum of Single-Domain Spherical Particles of αα IronIron
A small distribution
in K1 was required
11. Computer Simulations Using Different Convolution LinewidthsComputer Simulations Using Different Convolution Linewidths
Δ = (5/3)[2K1/Ms]
σp-p is the peak-to
-peak Lorentzian
linewidth.
Similar to spectrum
of α Fe particles in
silica glass
Similar to “characteristic”
resonance of lunar soils
Typical of
as-returned
lunar soils.
Typical of
annealed
lunar soils.
}
Similar to that
of annealed
lunar soils
∆
12. The Algebraic Sign of the MagnetocrystallineThe Algebraic Sign of the Magnetocrystalline
Anisotropy ConstantAnisotropy Constant
N.B. K1 is positive for metallic α iron.
13. N.B. K1 is negative for pure magnetite (Fe3O4) above ~130 K.
The Algebraic Sign of the MagnetocrystallineThe Algebraic Sign of the Magnetocrystalline
Anisotropy ConstantAnisotropy Constant
14. Magnetite-Like Phases in Simulated Lunar GlassesMagnetite-Like Phases in Simulated Lunar Glasses
HaveHave PositivePositive Magnetocrystalline Anisotropy Constants(!)Magnetocrystalline Anisotropy Constants(!)
Positive magnetocrystalline anisotropy is not proof of metallic iron!
All curves are magnetite-like phases in
simulated lunar glasses except the dashed
one, which is an Apollo 12 soil.
15. Simulated Lunar GlassesSimulated Lunar Glasses
Synthetic glasses of actual lunar compositions were melted under
extremely reducing conditions to yield the known mean valence state
of iron in lunar materials (Fe2+
). Sub-solidus oxidation darkens these glasses.
16. Simulation of Lunar “Fire Fountain” VocanismSimulation of Lunar “Fire Fountain” Vocanism
This process caused mild oxidation – and also stimulated precipitation
of small ferromagnetic particles similar to magnetite (Fe3O4).
This wonderful experimental rig
is due to the genius, initiative,
and toils of Charles Marquardt.
The temperatures of these
powdered simulated glasses
were held in the glass tran-
sition range of ~650 – 850 ºC.
17. The Apollo 15 Green Glass SpherulesThe Apollo 15 Green Glass Spherules
From J.W. Delano, Proc. 10th
Lunar Planet. Sci. Conf. (1979) 278.
Volcanic fire-fountain magma erupted from a depth of ~400 km
3.34 billion years ago
Sample 15426 (0.67 mm in horizontal dimension)
18. Simulated Lunar GlassesSimulated Lunar Glasses
Titanomagnetites are the source of magnetism in terrestrial rocks.
They consist of Fe3O4 with some iron ions substituted by Ti4+
.
Typical Lunar Soil Compositions Selected for Laboratory-Melted Glasses
Wt. %
ppm
}
19. Simulated Lunar Glasses vs. Apollo 15 Green SpherulesSimulated Lunar Glasses vs. Apollo 15 Green Spherules
FMR Linewidth FMR Intensity
0.3% TiO2
0.3% TiO2
0% TiO2
0% TiO2
Magnetite-like phases in simulated lunar glasses emulate A-15 green spherules!
Effect of TiO2 content demonstrated (would not occur if FMR due to metallic Fe).
Verwey
Transition
in Fe3O4
at ~130 K
20. Temperature Dependence of FMR LinewidthTemperature Dependence of FMR Linewidth
Linewidth data (Wp-p) for many
actual lunar samples and simulated
lunar glasses, each normalized to
unity at 300 K.
Note that none of the lunar samples
(five-numeral numbers + A-15 GGS)
precisely matches the data or theory
for Fe metal !
However, the Apollo 15 green glass
spherules almost exactly match the
data for magnetite-like phases in a
simulated lunar glass !
21. Temperature Dependence of FMR IntensityTemperature Dependence of FMR Intensity
Metallic Iron Magnetite
Verwey
Transition
in Fe3O4
at ~130 K
This trend
due to the
microwave
“skin effect”
in Fe metal
U “Inverted U”
behavior
22. Temp. Dependence of FMR Intensity of Lunar SoilsTemp. Dependence of FMR Intensity of Lunar Soils
Magnetite-like behavior evident in every sample
U
U
Apollo 17 Orange Soil
23. How Much “Magnetite” in Lunar Soils?How Much “Magnetite” in Lunar Soils?
GreenGlassSpherules
Fractional contribution of magnetite phases (based on temperature dependence) in blue.
Apollo17OrangeSoil
24. Correlation of FMR Linewidth with Lunar Soils ChemistryCorrelation of FMR Linewidth with Lunar Soils Chemistry
Correlation suggests titanomagnetites. Correlation suggests Ni-Fe alloys.
Data for as-received samples (○) and after in-vacuo heat treatment at 650 o
C for 3200 h (●).
Russian Unmanned
Probe, Luna-16
Lunar Volcanic
Glasses
25. Why Should There Be “Magnetite” in Lunar Soils?Why Should There Be “Magnetite” in Lunar Soils?
Undisputed Mean
Stoichiometry
of Lunar Rocks
Disproportionation
Disproportionation
Metallic Iron Magnetite
Heating above
560 C in reducing
atmosphere
produces metallic
Fe
But
Heating below
560 C in any
atmosphere
produces both
metallic Fe and
magnetite
26. Why Should There Be “Magnetite” in Lunar Soils?Why Should There Be “Magnetite” in Lunar Soils?
This uni-variant phase diagram due to Heiken and Williams ca. 1974
N.B. Pressures of this magnitude may apply
to the ~400 km depth in the Moon where
lunar fire-fountain volcanism has been
deduced by others to have originated…
Range of glass
transition
temperatures of
lunar glasses
Magnetite is Stable Here!
The most reducing gas
phases possible on the Moon:
27. Two-Domain Fe Particles in a Lunar Glass ChipTwo-Domain Fe Particles in a Lunar Glass Chip
(a) FMR of Single Domain
Magnetite and/or Metallic
Iron Particles in a Lunar
Soil (dashed curve) and
of Magnetite Precipitated
in a Simulated Lunar
Glass (solid curve).
(b) FMR of Something
Else in a Glass Chip from
an Apollo 11 Soil Sample
and Reproduction of the
Same Spectrum in a
Simulated Lunar Glass.
What Is It???
28. FMR Theory and Spectra of 2-Domain Fe ParticlesFMR Theory and Spectra of 2-Domain Fe Particles
Multiple
Domains
Can Exist
Multiple Domains
Cannot Exist
The experimental first-derivative spectra recorded at
3 frequencies ν have been numerically integrated.
MagneticFieldHnormalizedbystep-wisevariableν→
Saturation magnetization Ms divided by ν →
Case for H
parallel to
domain wall
Case for H
perpendicular
to domain
wall
29. Plagioclase fragments from an Apollo 14 Sample
Terrestrial Plagioclase Sample
Adapted from: R.A. Weeks (1973) J. Geophys. Res. 78, 2393.
Early Evidence of Fe3+ in Lunar MaterialsEarly Evidence of Fe3+ in Lunar Materials
