Magnetic ordering of the martensite phase in Ni-Co-Mn-Sn-based ferromagnetic shape memory alloys

TL;DR

This study clarifies the magnetic ordering in Ni-Co-Mn-Sn ferromagnetic shape memory alloys, demonstrating antiferromagnetic order in one alloy and spin glass behavior in another, resolving previous conflicting reports.

Contribution

It provides definitive experimental evidence distinguishing antiferromagnetic and spin glass states in different Ni-Co-Mn-Sn alloys, using combined magnetization, ac susceptibility, and neutron scattering techniques.

Findings

AF order in Ni45Co5Mn38Sn12 alloy

SG order in Ni44Co6Mn40Sn10 alloy

Nanometre-sized clusters grow from 3 nm to 11 nm with temperature

Abstract

The magnetic state of low temperature martensite phase in Co-substituted Ni-Mn-Sn-based ferromagnetic shape memory alloys (FSMAs) has been investigated, in view of numerous conflicting reports of occurrences of spin glass (SG), superparamagnetism (SPM) or long range anti-ferromagnetic (AF) ordering. Combination of dc magnetization, ac susceptibility and small angle neutron scattering (SANS) studies provide a clear evidence for AF order in martensitic phase of Ni45Co5Mn38Sn12 alloy and rule out SPM and SG orders. Identical studies on another alloy of close composition of Ni44Co6Mn40Sn10 point to presence of SG order in martensitic phase and absence of SPM behavior, contrary to earlier report. SANS results do show presence of nanometre-sized clusters but they are found to grow in size from 3 nm at 30 K to 11 nm at 300 K, and do not correlate with magnetism in these alloys.