Memory effect and magnetocrystalline anisotropy impact on the surface magnetic domains of magnetite(001)

© The Author(s) 2018 Tis research was partly supported by the Spanish Ministry of Economy and Competitiveness under Project No. MAT2015-64110-C02-1-P and MAT2014-52477-C5-2P. Experiments were performed at the National Center for Electron Microscopy Molecular Foundry, Lawrence Berkeley National Laboratory, supported by the Ofce of Science, Ofce of Basic Energy Sciences, Scientifc User Facilities Division, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. L.M.-G. thanks the MINECO for an FPI contract No. BES-2013- 063396.
The structure of magnetic domains, i.e. regions of uniform magnetization separated by domain walls, depends on the balance of competing interactions present in ferromagnetic (or ferrimagnetic) materials. When these interactions change then domain configurations also change as a result. Magnetite provides a good test bench to study these effects, as its magnetocrystalline anisotropy varies significantly with temperature. Using spin-polarized electron microscopy to map the micromagnetic domain structure in the (001) surface of a macroscopic magnetite crystal (similar to 1 cm size) shows complex domain patterns with characteristic length-scales in the micrometer range and highly temperature dependent domain geometries. Although heating above the Curie temperature erases the domain patterns completely, cooling down reproduces domain patterns not only in terms of general characteristics: instead, complex microscopic domain geometries are reproduced in almost perfect fidelity between heating cycles. A possible explanation of the origin of the high-fidelity reproducibility is suggested to be a combination of the presence of hematite inclusions that lock bulk domains, together with the strong effect of the first order magnetocrystalline anisotropy which competes with the shape anisotropy to give rise to the observed complex patterns.
Ministerio de Economía y Competitividad (MINECO)
Office of Science, Office of Basic Energy Sciences, Scientific User Facilities Division, of the U.S. Department of Energy
Depto. de Física de Materiales
Fac. de Ciencias Físicas
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