Ferromagnetism induced in UCoAl by uniaxial pressure

UCoAl exhibits attributes of an itinerant 5f-electron metamagnet. It is paramagnetic down to lowest temperatures but the c-axis susceptibility shows a maximum around T_max ≈ 20 K. When a field larger than B_c ≈ 0.6 T is applied along the c-axis of hexagonal structure a ferromagnetic ordering of U moments is induced at low temperatures. The critical parameters T_max and B_c are sensitive to alloying and hydrostatic pressure. In the latter case values of both, T_max and B_c, are increasing with increasing pressure, i.e. metamagnetism is suppressed towards a conventional paramagnetism. We report on results of an experiment with a c-axis uniaxial pressure, which has an opposite influence on T_max and B_c leading to ferromagnetism in zero field. A scenario of the physics of UCoAl is presented accounting for effects of hydrostatic- and uniaxial-pressure on the lattice and consequences in the 5f-electron delocalization and anisotropy of hybridization-mediated exchange interactions.