Local magnetic behavior across the first order phase transition in La(Fe0.9Co0.015Si0.085)13La(Fe0.9Co0.015Si0.085)13 magneto caloric compound

• A magneto optical investigation at the phase transition of a La(Fe0.9Co0.015Si0.085)13La(Fe0.9Co0.015Si0.085)13 was performed.
• Main and minor phases at the surface (above/below Tc) are distinguished and analyzed.
• Through the sample magneto static field we mapped spatially the 1st order transition.
• Different sources of thermal hysteresis of the magneto-caloric compound are identified.
• Magnetic defects exert a magnetic friction to the front propagation of the new phase.

We visualize, with a magneto optical imaging technique with indicator film, the local magnetic response of the compound La(Fe0.9Co0.015Si0.085)13La(Fe0.9Co0.015Si0.085)13 during its first order magneto structural transition. The technique allowed us by comparing the stray fields of the main magneto caloric phase and of secondary phases present in the sample to obtain the magnetic behavior of each phase above and below the Curie temperature with respect to the surrounds. Computing the change in the total magnetic flux, when the sample crosses the Curie point, both in cooling and heating, we are able to correlate the average thermal hysteresis of the transition with the local magnetic properties at single sites and analyze the influence of defects on the transition dynamics.

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