Quantum Critical Point in the Itinerant Ferromagnet Ni1−xRhx

Abstract

We report a chemical substitution-induced ferromagnetic quantum critical point in polycrystalline Ni1−xRhx alloys. Through magnetization and muon spin relaxation measurements, we show that the ferromagnetic ordering temperature is suppressed continuously to zero at xcrit = 0.375 while the magnetic volume fraction remains 100% up to xcrit, pointing to a second order transition. Non-Fermi liquid behavior is observed close to xcrit, where the electronic specific heat C el /T diverges logarithmically, while immediately above xcrit the volume thermal expansion coefficient αV /T and the Grüneisen ratio Γ = αV /C el both diverge logarithmically in the low temperature limit, further indication of a ferromagnetic quantum critical point in Ni1−xRhx.

Interstitial Atom Engineering in Magnetic Materials

“…From the fundamental viewpoint, research into critical behavior is interesting. Actually, in strongly correlated electron systems, there have been plenty of studies for seeking a quantum critical point under the suppression of magnetism [132][133][134][135][136]. We speculate that a formation of FM exchange coupling above room temperature would be a discontinuous phenomenon as mentioned in the results of Mn-based compounds.…”

Magnetic order and crystalline electric field excitations of the quantum critical heavy-fermion ferromagnet CeRh6Ge4

“…Conversely, ferromagnetic (FM) QCPs are not usually found [4] due to either a first-order disappearance of FM order [5,6] or the interjection of different ground states [7][8][9]. Theoretically, it was predicted that FM QCPs are forbidden in clean itinerant FM systems [10,11], and while there have been reports of their occurrence in some doped materials, including YbNi 4 (P 1−x As x ) 2 [12], CePd 0.15 Rh 0.85 [13], URh 1−x Ru x Ge [14], and Ni 1−x Rh x [15], in such cases a disorder driven suppression of the first-order transition is difficult to exclude.…”

Hyperscaling analysis of a disorder-induced ferromagnetic quantum critical point in Ni$_{1-x}$Rh$_{x}$ with $x = 0.375$

“…Our previous work on Ni 1−x Rh x presented thermodynamic evidence for a disorder-induced FM QCP in the vicinity of x c = 0.375 (see Fig. 1(a)) [25]. To the best of our knowledge, Ni 1−x Rh x is the only Ni 1−x A x alloy that exhibits a FM QCP.…”

“…That is, a set of critical exponents and the scaling functions are universal up to a certain symmetry and spatial dimensionality [27]. Here we report hyperscaling analysis of the low-temperature magnetization and specific heat data for Ni 1−x Rh x with x = 0.375, bearing all the features of a FM QCP [25]. The obtained scaling exponents are in line with the theoretical prediction for a FM fixed point in the asymptotic limit of high disorder [13,14].…”

“…The ordering temperature can be suppressed by alloying Ni with nonmagnetic or paramagnetic transition metals Ni 1−x A x [19][20][21][22]. The low-temperature quantum critical behavior has been extensively studied near the critical concentration x c in Ni 1−x Pd x [23], Ni 1−x V x [24], and Ni 1−x Rh x [25]. The former two alloys did not exhibit QCPs, but showed randomness in magnetic interactions caused by disorder: superparamagnetism was suggested to be responsible for constant thermal expansion coefficient as T → 0 in Ni 1−x Pd x [26], and additional disorder-induced fluctuations gave rise to a nonanalytic contribution to the free energy, forming so called the Griffiths rare regions, in Ni 1−x V x [24].…”