title: Magnetic force microscopy reveals meta-stable magnetic domain states that prevent reliable absolute palaeointensity experiments.
abstract: Obtaining reliable estimates of the absolute palaeointensity of the Earth's magnetic field is notoriously difficult. The heating of samples in most methods induces magnetic alteration--a process that is still poorly understood, but prevents obtaining correct field values. Here we show induced changes in magnetic domain state directly by imaging the domain configurations of titanomagnetite particles in samples that systematically fail to produce truthful estimates. Magnetic force microscope images were taken before and after a heating step typically used in absolute palaeointensity experiments. For a critical temperature (250 °C), we observe major changes: distinct, blocky domains before heating change into curvier, wavy domains thereafter. These structures appeared unstable over time: after 1-year of storage in a magnetic-field-free environment, the domain states evolved into a viscous remanent magnetization state. Our observations qualitatively explain reported underestimates from otherwise (technically) successful experiments and therefore have major implications for all palaeointensity methods involving heating.
authors.affiliation: Paleomagnetic laboratory Fort Hoofddijk, Department of Earth Sciences, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands.
authors.forename: Lennart V
authors.initials: LV
authors.lastname: de Groot
authors.affiliation: NGU, Geological Survey of Norway, Leiv Eirikssons vei, 7491 Trondheim, Norway.
authors.forename: Karl
authors.initials: K
authors.lastname: Fabian
authors.affiliation: Van't Hoff Laboratory for Physical and Colloid Chemistry, Department of Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Iman A
authors.initials: IA
authors.lastname: Bakelaar
authors.affiliation: Paleomagnetic laboratory Fort Hoofddijk, Department of Earth Sciences, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Dekkers