Ferromagnetic Resonance ofFerromagnetic Resonance ofPrecipitated Phases in Lunar Precipitated Phases in Lunar

GlassesGlasses

David L. GriscomDavid L. Griscomimpact Glass research internationalimpact Glass research international

Lote 454 Ranchitos, San Carlos, Sonora, MexicoLote 454 Ranchitos, San Carlos, Sonora, MexicoMail to: 3938 E Grant Rd #131, Tucson, AZ 85712Mail to: 3938 E Grant Rd #131, Tucson, AZ 85712

Presentation Presentation àà L’INSTN L’INSTN au Centre des Etudes Nucléaires de Saclay,au Centre des Etudes Nucléaires de Saclay,Gif-sur-Yvette, France, 19 May 2009Gif-sur-Yvette, France, 19 May 2009

Mare Imbrium

1214

16

11

17

15

Apollo Lunar Landing Sites

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

On the Moon with Apollo 15: View Across Hadley Rill On the Moon with Apollo 15: View Across Hadley Rill

Apennine Mountain Front

Mare Surface

Far side of Hadley Rill

Lunar Soil

Basalt Flow !

Morphologies of Lunar-Soil GlassesMorphologies of Lunar-Soil Glasses

The lunar soil (regolith) typically comprises up to 50% glass – mostly due to impacts

GlassyAgglutinates

Splash forms

Transmission Electron Micrograph of a TypicalTransmission Electron Micrograph of a TypicalLunar-Soil Glassy AgglutinateLunar-Soil Glassy Agglutinate

From: R.M. Housley, R.W. Grant, and N.E. Patton, Proc. Lunar Sci. Conf. 4 th (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...

• Source of microwavesf frequency MICROWAVE SOURCE

DETECTOR,AMPLIFIER

SAMPLE

X AXIS

Y AXIS

Abs

orpt

ion

Magnetic Field

FIELD PROBE

ELECTROMAGNETPOLE FACES

CHART RECORDER

• The microwaves are absorbed by unpaired electrons in the sample when h = gH + A, where h is Planck’s constant,

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

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

Ferromagnetic Resonance of Ferromagnetic Resonance of SphericalSpherical, , Single-DomainSingle-DomainSingle Crystals of Cubic StructureSingle Crystals of Cubic Structure

Angle of applied magnetic field, H, relative to thecrystallographic axes

Field position of resonanceline as function of angle

FMR spectrumaveraged overall angles

Measured parameters include the g value and magnetocrystalline anisotropy constant, K1.

HM

agni

tude

of H

→

(Ha = K1/Ms, where Ms is the saturation magnetization.)

K1

Powder Patterns

Simulated Spectra

Spectrum of Pure α Iron Precipitated in Silica Glass and Fitted Simulation Using Literature Values for g Value and MagnetocrystallineAnisotropy Constants, K1, K2, and K3.

D.L. Griscom (1981) J. Magn. Res. 45, 81-87.

FMR Spectrum of Single-Domain Spherical Particles of FMR Spectrum of Single-Domain Spherical Particles of αα Iron Iron

A small distributionin K1 was required

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 spectrumof α Fe particles insilica glass

Similar to “characteristic” resonance of lunar soils

Typical of as-returnedlunar soils.

Typical of annealedlunar soils.

Similar to thatof annealed lunar soils

The Algebraic Sign of the MagnetocrystallineThe Algebraic Sign of the MagnetocrystallineAnisotropy ConstantAnisotropy Constant

N.B. K1 is positive for metallic α iron.

N.B. K1 is negative for pure magnetite (Fe3O4) above ~130 K.

The Algebraic Sign of the MagnetocrystallineThe Algebraic Sign of the MagnetocrystallineAnisotropy ConstantAnisotropy Constant

Magnetite-Like Phases in Simulated Lunar GlassesMagnetite-Like Phases in Simulated Lunar GlassesHave Have PositivePositive Magnetocrystalline Anisotropy Constants(!) Magnetocrystalline Anisotropy Constants(!)

Positive magnetocrystalline anisotropy is not proof of metallic iron!

All curves are magnetite-like phases insimulated lunar glasses except the dashedone, which is an Apollo 12 soil.

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.

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.

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)

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

Simulated Lunar Glasses vs. Apollo 15 Green SpherulesSimulated Lunar Glasses vs. Apollo 15 Green SpherulesFMR 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).

VerweyTransitionin Fe3O4

at ~130 K

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 !

Temperature Dependence of FMR IntensityTemperature Dependence of FMR IntensityMetallic Iron Magnetite

VerweyTransitionin Fe3O4

at ~130 K

This trenddue to themicrowave“skin effect”in Fe metal

U“Inverted U”

behavior

Temp. Dependence of FMR Intensity of Lunar SoilsTemp. Dependence of FMR Intensity of Lunar Soils

Magnetite-like behavior evident in every sample

UU

Apollo 17 Orange Soil

How Much “Magnetite” in Lunar Soils?How Much “Magnetite” in Lunar Soils?

Gre

en G

lass

Sph

erul

es

Fractional contribution of magnetite phases (based on temperature dependence) in blue.

Apo

llo 1

7 O

rang

e So

il

Correlation of FMR Linewidth with Lunar Soils ChemistryCorrelation of FMR Linewidth with Lunar Soils ChemistryCorrelation suggests titanomagnetites. Correlation suggests Ni-Fe alloys.

Data for as-received samples (○) and after in-vacuo heat treatment at 650 oC for 3200 h (●).

Russian Unmanned Probe, Luna-16

Lunar Volcanic Glasses

Why Should There Be “Magnetite” in Lunar Soils?Why Should There Be “Magnetite” in Lunar Soils?Undisputed Mean

Stoichiometryof Lunar Rocks

Disproportionation

Disproportionation

Metallic Iron Magnetite

Heating above 560 C in reducing

atmosphereproduces metallic

Fe

ButHeating below 560 C in anyatmosphere

produces both metallic Fe and

magnetite

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:

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???

FMR Theory and Spectra of 2-Domain Fe ParticlesFMR Theory and Spectra of 2-Domain Fe Particles

MultipleDomainsCan Exist

Multiple Domains Cannot Exist

The experimental first-derivative spectra recorded at 3 frequencies have been numerically integrated.

Mag

netic

Fie

ld H

nor

mal

ized

by

step

-wis

e va

riabl

e

→

Saturation magnetization Ms divided by →

Case for H parallel to domain wall

Case for H perpendicular to domain wall

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