Evidence for magnetic clusters in Ni$_{1-x}$V$_{x}$ close to the quantum critical concentration

TL;DR

This study investigates magnetic behavior near the quantum critical point in Ni$_{1-x}$V$_{x}$, revealing magnetic clusters, a Griffiths phase, and a cluster-glass phase, highlighting the role of disorder in quantum phase transitions.

Contribution

It provides experimental evidence for magnetic clusters and Griffiths phase behavior near the quantum critical concentration in a disordered itinerant ferromagnet.

Findings

Presence of magnetic clusters near the critical concentration.

Observation of a Griffiths phase with power-law fluctuation rates.

Detection of a short-range ordered cluster-glass phase at low temperatures.

Abstract

The d-metal alloy Ni$_{1-x}$V$_{x}$ undergoes a quantum phase transition from a ferromagnetic ground state to a paramagnetic ground state as the vanadium concentration $x$ is increased. We present magnetization, ac-susceptibility and muon-spin relaxation data at several vanadium concentrations near the critical concentration $x_c \approx11.6%$ at which the onset of ferromagnetic order is suppressed to zero temperature. Below $x_c$, the muon data reveal a broad magnetic field distribution indicative of long-range ordered ferromagnetic state with spatial disorder. We show evidence of magnetic clusters in the ferromagnetic phase and close to the phase boundary in this disordered itinerant system as an important generic ingredient of a disordered quantum phase transition. In contrast, the temperature dependence of the magnetic susceptibility above $x_c$ is best described in terms of a magnetic quantum Griffiths phase with a power-law distribution of fluctuation rates of dynamic magnetic clusters. At the lowest temperatures, the onset of a short-range ordered cluster-glass phase is recognized by an increase in the muon depolarization in transverse fields and maxima in ac-susceptibility.