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

Abstract

We report magnetization 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)≈11.4%. In the diluted regime (x > x(c)), the temperature (T) and magnetic field (H) dependences 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.

Quantum Griffiths Phase Inside the Ferromagnetic Phase of Ni1−xVx

“…Close to the critical concentration x c ≈ 11.6%, the dependence of the low-temperature magnetization M on the magnetic field H is well described by anomalous power laws on both sides of the transition. On the paramagnetic side, M ∼ H α as in earlier work [11,12]. On the ferromagnetic side, we observe M − M 0 ∼ H α where M 0 is the spontaneous magnetization.…”

“…This was established for model Hamiltonians [3,4] and later predicted to occur in itinerant magnets [5,6], superconductors [7,8], and other systems (for reviews see, e.g., Refs. [9]).Signatures of a magnetic quantum Griffiths phase have been observed, e.g., in diluted Ce compounds [10] and, perhaps most convincingly, in the paramagnetic phase of the d-metal alloy Ni 1−x V x [11,12]. They consist in anomalous nonuniversal power-law dependencies of the magnetization, susceptibility and other thermodynamic quantities on temperature and magnetic field for concentrations x close to but above the quantum critical concentration x c (where the ferromagnetic transition temperature is suppressed to zero).…”

“…∆M also decreases for x < x c because it becomes less likely that a magnetic cluster remains disconnected from the bulk. By comparing ∆M with the typical cluster moment of 12 µ B [11,12], we estimate a cluster density at x c of about one cluster per 500 Ni atoms. Figure 3 To gain microscopic insight into these clusters and their dynamics, we employ µSR experiments (see, e.g., Ref.…”

Phases and phase transitions in disordered quantum systems

“…22. Ubaid-Kassis et al [112,113] performed magnetization and a.c. susceptibility measurements of several samples located just on the paramagnetic side of the quantum phase transition (samples with vanadium concentrations x between the critical concentration of about 11% and 15%). The results are summarized in Fig.…”

Composition induced metal–insulator quantum phase transition in the Heusler type Fe2VAl

“…The characteristic divergences are reminiscent of a quantum Griffiths phase, which occurs in many disordered correlated systems. The existence of a quantum Griffiths phase in the vicinity of the paramagnetic-ferromagnetic QCP has been confirmed by comprehensive measurements of thermodynamic quantities of transition metallic compounds such as Fe2+xV1−xAl [21], FeV1−xMxGa (M = Ti and Rh) [22], Ni1−xVx [23], and Fe1−xCoxS2 [24] and in the rare earth intermetallic compound Ce1−xLaxRhIn5 [25].…”