An article for magnetic heat exchange comprising a magnetocalorically active phase with a NaZn13-type crystal structure is provided by hydrogenating a bulk precursor article. The bulk precursor article is heated from a temperature of less than 50° C. to at least 300° C. in an inert atmosphere and hydrogen gas only introduced when a temperature of at least 300° C. is reached. The bulk precursor article is maintained in a hydrogen containing atmosphere at a temperature in the range 300° C. to 700° C. for a selected duration of time, and then cooled to a temperature of less than 50° C.
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