Large exchange bias in polycrystalline ribbons of Ni56Mn21Al22Si1

• Ni56Mn21Al22Si1 shows an orthorhombic 14M structure at room temperature.
• Spin glass behavior is observed below 68 K and superparamagnetic (SPM) above 60 K.
• Martensitic transformation temperatures are observed above 300 K.
• Large exchange bias (HEB) ~2.6 kOe is observed for cooling field (HCF) of 20 kOe.
• Large HEB is a consequence of a strong dependence of the SPM cluster size on HCF.

Large exchange bias (EB) effect is demonstrated in a Ni56Mn21Al22Si1 polycrystalline ribbon that shows spin-glass behaviour below 68 K and superparamagnetic (SPM) behaviour above this temperature. The average magnetic moment μ of the SPM clusters is estimated to be considerably smaller than that reported for other Heusler alloy systems that demonstrate spin glass behaviour and EB effect. The M–H loops measured in field-cooled (FC) conditions show significant asymmetry that is observed to be strongly field and temperature dependant. The maximum EB field (HEB ~2.6 kOe at 20 kOe and 2 K) is much larger than that reported for any metallic alloy system with conventional EB effect. The dependence of HEB on temperature shows an exponential decrease. An approach towards enhancement of the EB effect in this conventional EB system can be realized via manipulation of SPM or superferromagnetic (SFM) cluster size with variation of cooling magnetic field.