Spin fluctuations on the verge of a ferromagnetic quantum phase transition in Ni3Al1−xGa

Jingsong Yang

¹

,

Bin Chen

²

,

H. Ohta

³

et al.

Abstract

Ni 3 Al 1−x Ga x alloys are investigated by the measurements of isothermal magnetization, temperature variations of susceptibilities, and specific heats. Ga doping depresses the ferromagnetic transition temperature (T C ) continuously below the critical point x = 0.34. Near the critical region (x ≈ 0.34), the quantum critical scaling behaviors manifest themselves as the initial susceptibility χ −1 (T ) ∝ T 4/3 , T 4/3 C ∝ (x − x c ), and specific heat divided by temperature as C/T ∝ lnT at low temperatures. Furthermore, a novel spin-fluctuation spectrum was discovered in the samples near the quantum critical point, confirming the quantum critical point in this system. The magnetic properties in this system are understood almost in terms of the self-consistent renormalization and Takahashi's theory of spin fluctuations.

Metallic quantum ferromagnets

“…T C also decreases monotonically upon doping with Ga, leading to a QPT in Ni 3 Al 1−x Ga x at x c ≈ 0.34 (Yang et al, 2011); Ni 3 Ga is paramagnetic (Hayden et al, 1986). The disorder strength in these samples is not known, but assuming the same moderate disorder as in (Ni 1−x Pd x ) 3 Al one would expect Hertz-type critical behavior according to the theoretical analysis reviewed in Sec.…”

“…Ni3Al1−xGax and (Ni1−xPdx)3Al The FM order in Ni 3 Al with T C = 41 K (see Sec. II.B.1.d) can be suppressed by substitution of Pd for Ni (Sato, 1975), or by doping with Ga (Yang et al, 2011). In the former system, a QCP is reached at x ≈ 0.095, at which concentration the samples measured by Sato (1975) had a residual resistivity ρ 0 ≈ 10 µΩcm, indicating moderate disorder.…”

“…T C also decreases upon doing of Ni 3 Al with Pd (Sato, 1975) or Ga (Yang et al, 2011); these systems are discussed in Sec. II.C.1.b.…”

“…III.C.2, as is the logarithmic temperature dependence of the specific heat (Niklowitz et al, 2005;Sato, 1975;Yang et al, 2011). However, studies of the temperature dependence of the resistivity under pressure suggest that the QPT at the critical pressure is first order (Niklowitz et al, 2005;Pfleiderer, 2007).…”

Exponent relations at quantum phase transitions with applications to metallic quantum ferromagnets

“…35 This system is only moderately disordered, and critical behavior associated with the clean Hertz fixed point is expected to be observable in a sizable transient regime. 27 There are three experimental observations, from which four exponents can be deduced: (1) The critical temperature scales as T c ∼ r 3/4 , see the first panel in Fig.…”