Avoided ferromagnetic quantum critical point: Unusual short-range ordered state in CeFePO

TL;DR

This study investigates CeFePO, revealing short-range magnetic order that prevents reaching a ferromagnetic quantum critical point, with evidence of glassy, cooperative spin fluctuations distinct from typical spin glasses.

Contribution

It provides new insights into the magnetic behavior of CeFePO, showing an unusual short-range ordered state that avoids a ferromagnetic quantum critical point.

Findings

Short-range static magnetism appears below 0.7 K.

Muon-spin relaxation indicates glassy, cooperative spin fluctuations.

Behavior differs from canonical spin glasses and disorder-driven mechanisms.

Abstract

Cerium 4f electronic spin dynamics in single crystals of the heavy-fermion system CeFePO is studied by means of ac-susceptibility, specific heat and muon-spin relaxation ($\mu$SR). Short-range static magnetism occurs below the freezing temperature Tg ~ 0.7 K, which prevents the system from accessing the putative ferromagnetic quantum critical point. In the $\mu$SR, the sample-averaged muon asymmetry function is dominated by strongly inhomogeneous spin fluctuations below 10 K and exhibits a characteristic time-field scaling relation expected from glassy spin dynamics, strongly evidencing cooperative and critical spin fluctuations. The overall behavior can be ascribed neither to canonical spin glasses nor other disorder-driven mechanisms.