[Paper Review] Formation of short-range magnetic order and avoided ferromagnetic quantum criticality in pressurized LaCrGe$_3$

Elena Gati, John M. Wilde+12 more|Iowa State University Digital Repository (Iowa State University)|Nov 9, 2020

Magnetic and transport properties of perovskites and related materials4 citations

TL;DR

This study investigates the suppression of ferromagnetic quantum criticality in pressurized LaCrGe₃ using multi-technique experiments, revealing a first-order transition at ~1.5 GPa and the emergence of short-range magnetic order above this pressure, rather than long-range antiferromagnetic order. The results position LaCrGe₃ as a rare system bridging clean and weakly disordered itinerant ferromagnets near avoided quantum criticality.

ABSTRACT

LaCrGe$_3$ has attracted attention as a paradigm example of the avoidance of ferromagnetic (FM) quantum criticality in an itinerant magnet. By combining thermodynamic, transport, x-ray and neutron scattering as well as $μ$SR measurements, we refined the temperature-pressure phase diagram of LaCrGe$_3$. We provide thermodynamic evidence (i) for the first-order character of the FM transition when it is suppressed to low temperatures and (ii) for the formation of new phases at high pressures. From our microscopic data, we infer that short-range FM ordered clusters exist in these high-pressure phases. These results suggest that LaCrGe$_3$ is a rare example, which fills the gap between the two extreme limits of avoided FM quantum criticality in clean and strongly disordered metals.

Motivation & Objective

• To resolve the nature of the magnetic phase transition in LaCrGe₃ under high pressure, particularly near the avoided ferromagnetic quantum critical point.
• To determine whether long-range antiferromagnetic order or short-range magnetic correlations dominate in the high-pressure phase.
• To assess the role of weak disorder and competing FM/AFM interactions in stabilizing short-range order near the avoided quantum critical point.
• To refine the temperature-pressure phase diagram of LaCrGe₃ using thermodynamic, transport, and microscopic probes.

Proposed method

• Performed high-pressure transport, specific heat, and thermal expansion measurements to detect phase transitions and anomalies.
• Conducted x-ray and neutron diffraction to monitor lattice parameters and magnetic Bragg peak intensity changes.
• Applied muon spin rotation (µSR) to probe local magnetic fields and distinguish between long-range and short-range magnetic order.
• Analyzed anomalous contributions to thermodynamic quantities (ΔC/T, Δα) to identify critical behavior and phase transitions.
• Used neutron scattering to track the evolution of the (1 0 0) Bragg peak intensity, sensitive to magnetic ordering.
• Combined data across multiple techniques to construct a comprehensive temperature-pressure phase diagram.

Experimental results

Research questions

• RQ1 What is the nature of the magnetic transition in LaCrGe₃ as pressure suppresses the ferromagnetic transition to lower temperatures?
• RQ2 Does the high-pressure phase in LaCrGe₃ exhibit long-range antiferromagnetic order or short-range magnetic correlations?
• RQ3 Is the transition from second-order to first-order at ~1.5 GPa a signature of avoided quantum criticality in a clean itinerant ferromagnet?
• RQ4 To what extent does weak disorder or competing interactions drive the formation of short-range magnetic order near the avoided quantum critical point?
• RQ5 How do lattice distortions and volume changes correlate with the emergence of new magnetic phases under pressure?

Key findings

• The ferromagnetic transition in LaCrGe₃ becomes first-order at a tricritical point near 1.5 GPa, providing thermodynamic evidence for avoided ferromagnetic quantum criticality.
• Two distinct anomalies at T₁ and T₂ emerge at high pressure (≈1.9 GPa), indicating the formation of new magnetic phases above the first-order transition line.
• Below T₁, the magnetic volume fraction is strongly temperature-dependent, indicating dynamic short-range magnetic order rather than long-range order.
• Even below T₂ < T₁, the system retains a remanent magnetization, confirming the absence of long-range antiferromagnetic order and supporting short-range FM clustering.
• No significant lattice symmetry change is observed across T₁ and T₂, ruling out a spin-nematic phase with strong lattice coupling.
• The results suggest that LaCrGe₃ is a rare system exhibiting short-range magnetic order in a clean itinerant ferromagnet, bridging the gap between clean and strongly disordered systems near avoided quantum criticality.