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El magnetismo lamelar en la serie hematita-ilmenita como una explicación de la fuerte magnetización remanente
Peter Robinson1, Richard J Harrison, Suzanne A McEnroe
1Geological Survey of Norway, N-7491, Trondheim, Norway. peter.robinson@ngu.no
Nature
|August 2, 2002
Resumen
Una nueva subestructura magnética en óxidos de hierro-titanio explica la inusualmente fuerte remanencia en las rocas volcánicas. Este descubrimiento, que involucra capas de contacto ferroso-ferrico, revela un mecanismo para mejorar las propiedades magnéticas en los materiales geológicos.
Área de la Ciencia:
- La geofísica es la geofísica.
- Física de los minerales Física de los minerales
- Magnetismo de las rocas Magnetismo de las rocas.
Sus antecedentes:
- Las anomalías magnéticas en las rocas ígneas y metamórficas están típicamente vinculadas a la magnetita.
- Los minerales intermedios de la serie ilmenita-hematita pueden llevar una fuerte remanencia, pero generalmente se conserva solo en rocas volcánicas rápidamente enfriadas.
- Se ha observado una remanencia inusualmente grande y estable en rocas con intercrecimiento ilmenita-hematita, pero no se ha explicado completamente.
Objetivo del estudio:
- Investigar la causa de la magnetización inusualmente fuerte y estable de los remanentes naturales en las rocas volcánicas que contienen ilmenita y hematita.
- Proponer una nueva subestructura magnética que tenga en cuenta la remanencia magnética alta observada.
Principales métodos:
- Análisis de las láminas de exsolución en fases de óxido de hierro y titanio.
- Modelado teórico de las subestructuras magnéticas a nanoescala (hasta 1 nm).
- Estimación de la magnetización de saturación basada en el modelo propuesto.
Principales resultados:
- Lamelas de exsolución observadas con espesores que van desde 100 micrómetros hasta 1 nm.
- Propuso una nueva subestructura ferrimagnética que involucra "capas de contacto" de hierro y férrico entre la hematita y la ilmenita.
- Magnetización de saturación estimada de hasta 55 kA m(-1), significativamente más alta que la hematita pura, mientras se mantiene una alta coercitividad.
Conclusiones:
- Las "capas de contacto" ferroso-ferrónicas propuestas proporcionan un mecanismo para la magnetización remanente excepcionalmente fuerte observada en ciertas rocas volcánicas.
- Esta subestructura explica cómo las rocas con un contenido de óxido menor pueden exhibir anomalías magnéticas significativas.
- Los hallazgos tienen implicaciones para la comprensión de las firmas magnéticas en los registros geológicos y potencialmente para aplicaciones de materiales magnéticos.
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