Self-reversal of magnetization in oceanic submarine basalts studied with XMCD

In oceanic basalts, self-reversal of magnetization can be produced during extreme low-temperature oxidation of titanomagnetite by ionic reordering, which leads to Neel N-type magnetism. Titanomaghemites showing N-type reversal below room temperature were found in submarine basalts recovered during Ocean Drilling Program (ODP) Leg 197. In order to better understand the mechanism of self-reversal, we carried out X-ray magnetic circular dichroism (XMCD) at Fe K-edge at room temperature and low-temperature on such a titanomaghemite sample as well as on pure magnetite and maghemite samples. We found that the XMCD spectrum of the N-type titanomaghemite at 20 K is a mirror image of the XMCD spectrum at 300 K, which shows that the octahedral and tetrahedral subnetworks reverse in this process. Ligand-field multiplet calculations of XMCD at Fe K-edge help identify the contributions of the different elements in the measured XMCD spectra. This mechanism could also cause self-reversal above room temperature, which has important consequences for the reliability of paleomagnetic measurements. Citation: Carvallo, C., P. Sainctavit, M.-A. Arrio, Y. Guyodo, R. L. Penn, B. Forsberg, A. Rogalev, F. Wilhelm, and A. Smekhova (2010), Self-reversal of magnetization in oceanic submarine basalts studied with XMCD, Geophys. Res. Lett., 37, L11306, doi: 10.1029/2010GL043390.