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Majumder, M.; Wagner-Reetz, M.; Cardoso-Gil, R.; Gille, P.; Steglich, F.; Grin, Y.; Baenitz, M. (2016): Towards ferromagnetic quantum criticality in FeGa3−xGex:71Ga NQR as a zero-field microscopic probe. In: Physical Review B, Vol. 93, No. 6, 64410
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Abstract

Ga-71 NQR, magnetization, and specific-heat measurements have been performed on polycrystalline Ge-doped FeGa3 samples. A crossover from an insulator to a correlated local moment metal in the low-doping regime and the evolution of itinerant ferromagnet upon further doping is found. For the nearly critical concentration at the threshold of ferromagnetic order, x(C) = 0.15, (71)(1/T1T) exhibits a pronounced T-4/3 power law over two orders of magnitude in temperature, which indicates three-dimensional quantum critical ferromagnetic fluctuations. Furthermore, for the ordered x = 0.2 sample (T-C approximate to 6K), (71)(1/T1T) could be fitted well in the frame of Moriya's self-consistent renormalization theory for weakly ferromagnetic systems with 1/T1T similar to chi. In contrast to this, the low-doping regime nicely displays local moment behavior where 1/T1T similar to chi(2) is valid. For T -> 0, the Sommerfeld ratio gamma = (C/T) is enhanced (70 mJ/mole K-2 for x = 0.1), which indicates the formation of heavy 3d electrons.