Unusual ferromagnetic critical behavior owing to short-range antiferromagnetic correlations in antiperovskite Cu1-xNMn3+x(0.1<x<0.4)

TL;DR

This study uncovers unusual critical magnetic behavior in Cu1-xNMn3+x manganese nitrides caused by short-range antiferromagnetic correlations, revealing deviations from universal classes and the influence of composition on critical fluctuations.

Contribution

It demonstrates the impact of short-range antiferromagnetic correlations on critical behavior and the deviation from universal classes in manganese nitrides.

Findings

Critical fluctuations above TC are robust at x=0.1 and weaken with increasing x.

Paramagnetic susceptibility deviates from Curie-Weiss law above TC, especially at lower x.

Short-range antiferromagnetic order explains the unusual critical behavior and susceptibility deviations.

Abstract

For ferromagnets, varying from simple metals to strongly correlated oxides,the critical behaviors near the Curie temperature (TC) can be grouped into several universal classes. In this paper, we report an unusual critical behavior in manganese nitrides Cu1-xNMn3+x(0.1<x<0.4). Although the critical behavior below TC can be well described by mean field (MF) theory, robust critical fluctuations beyond the expectations of any universal classes are observed above TC in x=0.1. The critical fluctuations become weaker when x increases, and the MF-like critical behavior is finally restored at x=0.4. In addition, the paramagnetic susceptibility of all the samples deviates from the Curie-Weiss (CW) law just above TC. This deviation is gradually smeared as x increases. The short-range antiferromagnetic ordering above TC revealed by our electron spin resonance measurement explains both the unusual critical behavior and the breakdown of the CW law.