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Hoffman, K. A.

Publications and source records attributed to Hoffman, K. A..

Combining paleointensity methods - A dual-valued determination on lunar sample 10017,135

A single-heating procedure for the determination of two partially independent values of paleofield intensity for one sample is presented. The procedure combines data for Shaw-type and 'ARM-method' determinations furnishing the ratio thermoremanent magnetization (TRM) to ARM acquisition efficiency corrected for physicochemical alteration to the magnetic carriers. Applicability of the Shaw-method to Fe-bearing samples is demonstrated by simulated paleointensity determinations on synthetic samples containing multidomain grains. The combined Shaw-ARM procedure was applied to a linear basalt sample, but the Thellier-Thellier method could not provide a meaningful determination of the neighboring chip. These conflicting findings may be explained by multiple step-wise heatings causing more damage to carriers than a single heating procedure, and by the natural remanent magnetization in this lunar basalt not being a simple TRM.

Hoffman, K. A.↗

Magnetic 'zig-zag' behavior in lunar rocks

A lunar olivine basalt sample is analyzed which exhibits unorthodox alternating field (AF) demagnetization behavior characterized by nonreproducible remanent magnetization values upon demagnetization at a given peak AF. It is shown that the direction of the remanence following AF demagnetization is roughly confined to a particular plane and that this behavior is an intrinsic property of certain magnetic carriers present in the sample. The viscous acquisition coefficient is found to be about 1-1/2 times greater than the absolute value of the decay coefficient. It is suggested that the behavior of this sample is due to the presence of a few planar, multidomain grains which represent a local mineral fabric, do not demagnetize, and may interfere with the determination of a meaningful time variation of lunar magnetic paleointensity.

Hoffman, K. A.↗