Magnetic properties of weak itinerant electron ferromagnets FexCo1−xSi under high pressure

High-pressure AC magnetic susceptibility measurements have been carried out for the weak itinerant-electron ferromagnet FexCo1−x  Si with x=0.3x=0.3, 0.4, 0.5 and 0.7 using a cubic anvil apparatus up to 7.5 GPa in the temperature range from 4.2 to 300 K in order to investigate their itinerant-electron ferromagnetic character under high pressure. The slope of the curves of the temperature dependence of the susceptibility around the Curie temperature TC was found to become steeper with pressure for the alloys with x=0.4 and 0.5. It suggests a change in the magnetic phase transition from the second to the first order to occur at higher pressure for these alloys by analogy from the case of MnSi that is a weak itinerant-electron ferromagnet with the same crystal structure as FexCo1−xSi. It was found that for all alloys TC obeys 34 power law of pressure derived from the SCR theory. Pressure derivative of the ratio TC/T0, where T0 is the spin fluctuation parameter, was roughly estimated for all alloys using the data of the macroscopic magnetic measurements.