MOSSBAUER-EFFECT STUDY OF PD-BASED HEUSLER ALLOYS .1. MAGNETIC COUPLING

Mossbauer effect experiments have been performed on Heusler alloys from the series Pd2MnIn1-xSnx (0.01<or=x<or=1.0) and Pd2MnIn1-ySby (0.1<or=y<or=0.5) using the isotopes 119Sn and 121Sb respectively. Spectra were recorded with the samples at 4.2K which was well below the magnetic transition temperature in all cases, and at room temperature where all alloys were paramagnetic. Due to the atomic disorder on the Z site in the alloys, distribution of hyperfine fields were observed at 4.2K in most cases. The magnetic phases of the alloys were determined from the behaviour of the spectra upon application of external magnetic fields of up to 6 T. At 4.2K the alloys with x<or=0.4 (or y<or=0.2) were antiferromagnetic those with x>or=0.7 (or y>or=0.4) were ferromagnetic while those in the intermediate regions contained more than one magnetic phase, in agreement with previously published neutron diffraction data. It is concluded that the magnetic coupling depends sensitively on the conduction electron concentration, and that the Mn-Mn exchange interaction is dominated by long-range coupling via the conduction electrons.