Determining Demagnetization Energy and Internal Stress in Natural Magnetite Bearing Samples

The stability and acquisition of remanent magnetization in Earth and planetary rocks is controlled by the magnetization state of magnetic particles. Magnetic properties are often characterized by magnetic grain size. Besides grain size, also stress, magnetostatic interactions, and grain shape influence and modify magnetic stability. Moreover, internal stress in magnetite may substantially affect remanence acquisition and might be responsible for enhanced remanence for which the processes are often still enigmatic.

To better understand the impact of internal stress on the efficiency of remanence acquisition, their contribution needs to be separated from the magnetostatic and demagnetizing energy contributions. Direct observations of the influences of magnetocrystalline and stress anisotropy on the magnetic behavior of magnetite are obscured by the large demagnetizing energy. A new temperature-dependent hysteresis measurement and evaluation procedure was developed by Béguin & Fabian, (2021), which allows the determination and separation of demagnetizing energy and internal stress. The validity of the method was demonstrated for a suite of synthetic magnetite samples under different stress conditions.

Here we present the first results of applying the new scaled reversible work (SRW) method to a set of natural magnetite bearing samples. We used samples with homogeneous and heterogeneous microstructures and end-member stress-free magnetite samples. The magnetic behavior as function of temperature is less ideal for the natural samples than for the previously studied synthetic magnetite samples, for example, the Curie temperatures are less distinct. Here we present how these challenges can be overcome, and present additional evaluation steps to ease the interpretation of the temperature-dependent hysteresis data.