Quantum Griffiths Phase in the weak itinerant ferromagnetic alloy Ni1−x_{1-x}Vx_x

We present magnetization ($M$) data of the $d$-metal alloy Ni$_{1-x}$V$_x$ at vanadium concentrations close to $x_c \approx 11.4$ where the onset of long-range ferromagnetic (FM) order is suppressed to zero temperature. Above $x_c$, the temperature ($T$) and magnetic field ($H$) dependencies of the magnetization are best described by simple nonuniversal power laws. The exponents of $M/H \sim T^{-\gamma}$ and $M \sim H^\alpha$ are related by $1-\gamma=\alpha$ for wide temperature ($10K < T \leq 300K$) and field ($H \leq 5T$) ranges. $\gamma$ is strongly $x$ dependent, decreasing from 1 at $x\approx x_c$ to $\gamma < 0.1$ for x=15%. This behavior is not compatible with either classical or quantum critical behavior in a clean 3D FM. Instead it closely follows the predictions for a quantum Griffiths phase associated with a quantum phase transition in a disordered metal. Deviations at the lowest temperatures hint at a freezing of large clusters and the onset of a cluster glass phase, presumably due to RKKY interactions in this alloy.Comment: 4 pages, 4 pdf figures included, final version as published

Signatures of a quantum Griffiths phase in a d-metal alloy close to its ferromagnetic quantum critical point

We report magnetization ($M$) measurements close to the ferromagnetic quantum phase transition of the d-metal alloy Ni$_{1-x}$V$_x$ at a vanadium concentration of $x_c \approx 11.4$. In the diluted regime ($x>x_c$), the temperature ($T$) and magnetic field ($H$) dependencies of the magnetization are characterized by nonuniversal power laws and display $H/T$ scaling in a wide temperature and field range. The exponents vary strongly with $x$ and follow the predictions of a quantum Griffiths phase. We also discuss the deviations and limits of the quantum Griffiths phase as well as the phase boundaries due to bulk and cluster physics.Comment: 4 pages, 5 figures, final version as published in the Strongly Correlated Electron Systems special issue of J. Phys. Condens. Matte

Quantum Griffiths Phase in the Weak Itinerant Ferromagnetic Alloy Ni₁₋ₓVₓ

We present magnetization (M) data of the d-metal alloy Ni1-xVx at vanadium concentrations close to xx ~ 11.4% where the onset of long-range ferromagnetic (FM) order is suppressed to zero temperature. Above xc, the temperature (T) and magnetic field (H) dependencies of the magnetization are best described by simple nonuniversal power laws. the exponents of M/H ~ T γ and M ~ Hα are related by 1-γ=α for wide temperature (10c to γ\u3c0.1 for x=15%. This behavior is not compatible with either classical or quantum critical behavior in a clean 3D FM. Instead it closely follows the predictions for a quantum Griffiths phase associated with a quantum phase transition in a disordered metal. Deviations at the lowest temperatures hint at a freezing of large clusters and the onset of a cluster glass phase

Quantum Griffiths Phase Inside the Ferromagnetic Phase of Ni₁₋ₓVₓ

We study by means of bulk and local probes the d-metal alloy Ni1-xVx close to the quantum critical concentration, xc ≈ 11.6%, where the ferromagnetic transition temperature vanishes. The magnetization-field curve in the ferromagnetic phase takes an anomalous power-law form with a nonuniversal exponent that is strongly x dependent and mirrors the behavior in the paramagnetic phase. Muon spin rotation experiments demonstrate inhomogeneous magnetic order and indicate the presence of dynamic fluctuating magnetic clusters. These results provide strong evidence for a quantum Griffiths phase on the ferromagnetic side of the quantum phase transition

Quantum Griffiths phase inside the ferromagnetic phase of Ni1-xVx

We study by means of bulk and local probes the d-metal alloy Ni1-xVx close to the quantum critical concentration, x_c \approx 11.6\%, where the ferromagnetic transition temperature vanishes. The magnetization-field curve in the ferromagnetic phase takes an anomalous power-law form with a nonuniversal exponent that is strongly x-dependent and mirrors the behavior in the paramagnetic phase. Muon spin rotation experiments demonstrate inhomogeneous magnetic order and indicate the presence of dynamic fluctuating magnetic clusters. These results provide strong evidence for a quantum Griffiths phase on the ferromagnetic side of the quantum phase transition