Abstract
The evolution of magnetic properties of isostructural and isoelectronic solid solutions of the superconducting itinerant -electron ferromagnet (FM) UCoGe with antiferromagnet (AFM) UIrGe was studied by magnetization, AC susceptibility, specific heat, and electrical resistivity measurements of a series of compounds in polycrystalline and single-crystalline form at various temperatures and magnetic fields. Both the weak FM and superconductivity in UCoGe were found to have vanished already for very low Ir substitution for Co . The AFM of UIrGe is gradually suppressed. This is documented by a rapid decrease in both Néel temperature and the critical field of the metamagnetic transition with decreasing Ir concentration, which both tend to vanish just above . The section of the phase diagram in the range is dominated by a correlated paramagnetic phase (CPM) exhibiting very broad bumps in temperature dependencies of -axis magnetization and specific heat developing with increasing . For , wide peaks appear in the -axis thermomagnetic curves due to AFM correlations which may eventually lead to frozen incoherent spin configurations at low temperatures. The CPM is also accompanied by specific electrical resistivity anomalies. The phase diagram determined for the compounds contrasts with the behavior of the related system, which was reported to exhibit an extended concentration range of stable FM in Rh-rich compounds and a discontinuous transformation between the FM and AFM phases at a critical Rh-Ir concentration. The striking difference is tentatively attributed to (a) the instability of tiny U moment in the weak itinerant FM UCoGe induced by substitutional disorder at already very low Ir doping, (b) the rather stable U moment in URhGe formed by much less delocalized electrons assisted by weakly varying lattice parameters of compounds.
1 More- Received 18 June 2021
- Revised 8 January 2022
- Accepted 11 January 2022
DOI:https://doi.org/10.1103/PhysRevB.105.014436
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