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Results of fundamental and third order ac susceptibility measurements in a Ni49Mn29Ga22 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. [ABSTRACT FROM AUTHOR]

• B2 structured Ni-Mn-Al thin film has been successfully deposited by Co-sputtering. • Observation of large exchange bias field at low temperature. • Field induced FM ordering at temperature ~50 K. • The negative interface exchange constant. • AFM coupling between the coexisting phases. In the present work exchange bias in Mn rich Ni-Mn-Al film has been studied. The film has been deposited by cosputtering from the targets of Ni, Mn and Al. It exhibits an antiferromagnetic B2 phase at room temperature. At low temperature, magnetization versus temperature (M - T) measurement shows a bifurcation among ZFC and FC curves. Hysteresis (M-H) loops measurements reveal the occurrence of exchange bias phenomenon at low temperature. Large H EB of 2.2 kOe for 20 kOe cooling field has been observed. There occurs a field induced ordering at temperature ~50 K reflected as coinciding ZFC (zero-field cooled) and FC (field-cooled) curves at large magnetic field. AC susceptibility measurement indicates the occurrence of cluster glass behaviour at low temperature. The exchange constant obtained from the best fit to the experimental data was found to be Ji ≈ −2 meV. The negative interface exchange constant indicates AFM coupling occurs among the coexisting phases. Exchange bias phenomenon may be associated to the coexistence of antiferromagnetic and ferromagnetic like ordering at low temperature. Cooling field dependence of H EB and coercive field H C indicate that an increase in anisotropy and growth of ferromagnetic clusters occurs at high magnetic field. [ABSTRACT FROM AUTHOR]