Alloying driven transition between ferro- and antiferromagnetism in UTGe compounds: the UCo1-xIrxGe case

The fundamental study of the magnetic features of isostructural and isoelectronic system UCo1−xIrxGe mixing superconducting itinerant 5f-electron ferromagnet UCoGe and antiferromagnet UIrGe was carried out. We used magnetization, heat capacity, and electrical resistivity measurements performed on series of UCo1−xIrxGe polycrystalline samples to probe the physical properties. The weak ferromagnetism of UCoGe was observed to disappear already for the lowest Ir doping (x = 0.005). On the other hand, traces of the superconducting state were detected up to x = 0.01. Moving from the UIrGe side, the antiferromagnetism moderately vanishes upon decreasing Ir concentration completely disappearing at x  0.75. The middle part of the T-x phase diagram in the range 0.005  x < 0.75 is dominated by a paramagnetic phase. We propose a scenario of competition of ferromagnetic and antiferromagnetic interactions leading to the paramagnetic state. Upon gradually increasing Ir concentration, antiferromagnetic correlations which may result in frozen incoherent spin configurations at low temperatures, emerge in the paramagnetic state at x  0.4. When comparing UCo1−xIrxGe system to the related URh1-xIrxGe one reported exhibiting an FM/AFM discontinuity in concentration dependence a clear contrast of the evolution of magnetic state can be noticed. We ascribe the difference to the different degrees of 5f-electron localization in UCoGe and URhGe.