Abstract
In magnetocaloric La(Fe,Si)13 alloys, it is known that hydrogen addition shifts the magnetic transition temperature TC near room temperature. By partial hydrogen desorption, TC can be adjusted precisely towards the working temperature of a magnetic cooling device. In this work, we studied the stability of partially desorbed LaFe11.6Si1.4Hy and show that the large volume difference of ferro- and para-magnetic phases drives the system from a single phase to a stable two-phase configuration. The hydrogen concentration separates on a macroscopic scale. The phase-coexistence is visualized by Kerr Microscopy. Differential scanning calorimetry measurements show that hydrogen can be reversibly recombined and separated again. We explain the separation by the coexistence of a high-volume ferromagnetic and low-volume paramagnetic phase that can be induced either by temperature or other external stimuli. This phenomenon can be applied to material systems that show a coupling of physical and structural transitions.
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