Effect of chemical disorder on Griffiths phase in weak itinerant ferromagnetic Ni92−xCuxCr8 alloy

We report magnetic and thermal properties of Cu substituted Ni 92-x Cu x Cr 8 polycrystalline alloys close to their critical concentration ( x c ~ 18%), where ferromagnetic order disappears. From the detailed analysis of field and temperature dependent magnetization data weak itinerant ferromagnetic character has been identified for the compositions below x c . Spin-fluctuations theory using the Ginzburg–Landau formalism further revealed the contributions of spin fluctuations, which increase near x c . Specific heat data shows unusual low-temperature variation with an enhanced Sommerfeld coefficient and non Fermi-liquid behavior due to strong magnetic fluctuations near x c . The magnetization data and the linear term of the specific heat follow the theoretical predictions of a ferromagnetic quantum critical point within the experimental uncertainties. The exponent of the power-law M(H) ∝ H λ fits to low-temperature magnetic isotherms and its variation with composition indeed suggests a possibility of quantum Griffiths phase in these alloy compositions. Finally, this study shows that the Cu substituted Ni-Cr system shows Griffiths phase at critical point even after the reduction of disorder. • Weak itinerant ferromagnetic Ni-Cr alloy was driven into paramagnetic state through chemical disorder i.e, by substituting about 17 at% of non-magnetic Cu in place of Ni. • Rhodes–Wolhfarth Ratio ( RWR = p c p s ) was evaluated from M (T) and M(H) magnetization data and found it to be greater than 1, which signifies weak itinerant behavior of all FM compositions. • A transition from Fermi liquid to non-Fermi liquid like behavior is evidences through the analysis of specific heat data. • We have also quantified the contribution of spin fluctuations and shown in to be dominant near critical concentration. • The non- universal Griffiths exponent (λ) from the low temperature magnetic isotherms has been evaluated. Its variation with composition clearly shows a Griffith singularity at critical concentration of x c (17.79 ± 0.16).