Compressibility Anomaly in Magnetic Heuslar Alloy Ni2MnGa and Co2FeSi

Results of synchrotron based high pressure x ray diffraction measurements on Heuslar alloys Ni2MnGa and Co2FeSi are reported up to 30.6 and 24.6 GPa respectively. Pressure volume data for Ni2MnGa shows normal compressibility behaviour up to 30.6 GPa with the value of bulk modulus Bo and its pressure derivative B' as 130 GPa and 4.97 respectively. In case of Co2FeSi, the P-V data shows normal behaviour upto 5 Gpa and hereafter linear P-V relation. The estimated ambient pressure compressibility based on data up to 5 GPa is 267 GPa (with B'=4). The fit to linear P-V data above 5 GPa yields a compressibility of 279.5.