We visualize, with a magneto optical imaging technique with indicat or film, the local magnetic response of the compound La FeCoSi 0.9 0.0150.08513 ( ) 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 Curietem perature 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, weare able to correlate the average thermal
hysteres is of the transition with the local magnetic properties at single sites and analyze the influence of defects on the transition dynamics.