A low temperature anomaly observed in off-stoichiometric Ni-Mn-Ga system studied by higher harmonic ac-susceptibility measurements

摘要

Results of fundamental and third order ac susceptibility measurements in a Ni_(49)Mn_(29)Ga_(22) single crystal demonstrate that higher harmonics of ac-susceptibility measurement is an excellent tool to identify transitions/anomalies originating from different magnetic substructures that remain undetected by usual dc susceptibility measurements. Anomaly observed at low temperature (～ 150 K) has also been explored by differential scanning calorimetry, temperature dependent x-ray diffraction, and transmission electron microscopy measurements. The results demonstrate that the magnetic subsystem in Ni-Mn-Ga is unstable at low temperatures not only for metastable modulated crystal structure but also for very stable nonmodulated tetragonal structure.