Magnetism and associated exchange bias in Ni2−xCoxMn1.4Ga0.6

• The magnetic properties and associated exchange bias of Ni2-xCoxMn1.4Ga0.6 have been investigated.
• Ferromagnetic and antiferromagnetic interactions co-exist in the alloys.
• The competing interactions results in interesting magnetic properties.
• AC susceptibility data shows the existence of spin glass and super spin glass interactions.

A series of Ni2−xCoxMn1.4Ga0.6 Heusler alloys have been systematically investigated by x-ray diffraction, dc magnetization, and ac susceptibility measurements. For all Co concentration, the alloys exhibit the L10 martensitic structure at room temperature. Interestingly, Co doping simultaneously causes a reduction in the ferromagnetic exchange interaction and enhancement of magnetic anisotropy in Ni2−xCoxMn1.4Ga0.6. Exchange bias effects under both zero field cooled and field cooled condition have been observed in all alloys for x<0.3. The ac susceptibility data show frequency dependence that changes with increasing Co concentration, indicating a change of ground state from spin glass to super spin glass. The experimental results are explained considering the atomic radii of Ni and Co and the fundamental magnetic interactions in Heusler alloys.