Abstract
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 (~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.
Highlights
Cycling a macroscopic crystal of magnetic material between above and below its Curie temperature (Tc) usually results in the formation of magnetic domain patterns in the low temperature phase1,2
Using a variable temperature spin-polarized low-energy electron microscope (SPLEEM)16 we detected that the spin reorientation transition takes place in two stages with a discontinuous change of magnetization followed by a continuous one
In this work we focus on the evolution and fate of the magnetic domains on magnetite (001) at high temperatures, from the Tsrt up to the Curie point
Summary
Cycling a macroscopic crystal of magnetic material between above and below its Curie temperature (Tc) usually results in the formation of magnetic domain patterns in the low temperature phase. In some cases, such as when the characteristic length scale of domain sizes is similar to sample size, the domain patterns in the low temperature phase approach energy minimum configurations; one example is the stability of Landau closure domains in small magnetic particles In such cases the observed geometry of domains may be reproduced in detail after each heating/cooling cycle. Both the (111) and the (100) lack easy-axes within the surface plane Thereby they correspond to the case of strongly-misoriented magnetic surfaces, where the competition between anisotropies is expected to give rise to complex patterns. In this work we focus on the evolution and fate of the magnetic domains on magnetite (001) at high temperatures, from the Tsrt up to the Curie point
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