Tunable negative thermal expansion related with the gradual evolution of antiferromagnetic ordering in antiperovskite manganese nitrides Ag1-xNMn3+x (0<x<0.6)

TL;DR

This study investigates how substituting Mn for Ag in antiperovskite manganese nitrides extends negative thermal expansion to cryogenic temperatures and links magnetic phase evolution with thermal properties.

Contribution

It reveals the tunability of negative thermal expansion through compositional changes and correlates magnetic ordering evolution with volume change in Ag1-xNMn3+x.

Findings

Negative thermal expansion broadens and shifts to cryogenic temperatures with Mn substitution.

Multiple magnetic transitions, including PM-FM and AFM, are observed and linked to volume changes.

Electron spin resonance indicates a close relationship between AFM ordering and volume change near T*.

Abstract

The thermal expansion and magnetic properties of antiperovskite manganese nitrides Ag1-xNMn3+x were reported. The substitution of Mn for Ag effectively broadens the temperature range of negative thermal expansion and drives it to cryogenic temperatures. As x increases, the paramagnetic (PM) to antiferromagnetic (AFM) phase transition temperature (TN) decreases. At x~0.2, the PM-AFM transition overlaps with the AFM to glass-like state transition. Above x=0.2, two new distinct magnetic transitions were observed: one occurs above room temperature from PM to ferromagnetic (FM), and the other one evolves at a lower temperature (T*) below which both AFM and FM orderings are involved. Further electron spin resonance measurement suggests that the broadened volume change near T* is closely related with the evolution of {\Gamma}5g AFM ordering.