Physics
Scientific paper
Jun 1975
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975gecoa..39..889s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 39, Issue 6-7, pp.889-902
Physics
2
Scientific paper
Magnetic hysteresis properties have been measured for single-phase spinels (as determined by X-ray diffraction) of the solid solution series Fe(Fe x Cr 2- x )O 4 synthesized at 1573°K and oxygen fugacities in the range 10 -3 -10 -10 atm. The spinel solid solution series can be divided into three regions on the basis of characteristics of the magnetic hysteresis loops at 300°K. Region I (1.3 x 2.0) is characterized by hysteresis loops typical of single-phase ferrimagnetic spinels, whereas region II (0.7 x 1.3) and region III (0 x 0.7), respectively, are characterized by constricted hysteresis loops and by hysteresis loops typical of twophase materials. The hysteresis loops for samples in region I are similar to those obtained for the solid solution series MgFe 2 O 4 -MgCr 2 O 4 synthesized at 1573°K in air. The hysteresis loops measured at 77°K for field-cooled samples from regions II and III show shifted loops and magnetic viscous behavior. These features are interpreted as indicating magnetic exchange anisotropy involving coupling of the spin system of the host ferrimagnetic spinel with that of an antiferromagnetic wüstite-type submicroscopio phase or microstate. It is suggested that the presence of the microstate is due to incipient reduction. This interpretation is consistent with the phase relations and previously established magnetic properties of the oxide phases in the system FeO-Fe 2 O 3 -Cr 2 O 3 . Also consistent with the hypothesis of reduction-induced inhomogeneities in the iron-chromium spinels are the observations of similarly `anomalous' magnetic properties in naturally and experimentally reduced basaltic rocks and in certain titaniumchromium-bearing spinels. The techniques described provide a new approach to phase characterization that is more sensitive to the redox condition of spinels than conventional techniques of X-ray diffraction, electron microprobe analysis, and optical microscopy.
Schwerer F. C.
Ulmer Gene C.
Virgo David
Wasilewski Peter
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