Fig. 9

Schematic view of the proposed phase diagram in the immediate vicinity of the tricritical point (TCP) in the temperature (T)—magnetic field (H)—control parameter (p) space based on the experimental data. Within presented study, the control parameter is either hydrostatic pressure or substitution. Starting at high temperatures and H = 0 the second order transition is indicated by dashed line, spreading to non-zero field as second order transition plane (light blue surface). Below TCP (H = 0, solid line) and crossover temperature T ₀ for H ≠ 0 (dark blue) the transition becomes first order accompanied by the presence of hysteresis (for simplicity indicated only for H = 0). Planes for fixed p indicate position of samples used in this study—green (UCo_0.990Ru_0.010Al), red (UCo_0.995Ru_0.005Al) and brown (UCoAl). The red line indicate the phase transition line (μ ₀ H _c ) for the UCo_0.995Ru_0.005Al as shown in Fig. 3, indicating both first-order (solid) and second-order (dashed) transition. For simplicity, the phase boundaries are sketched only for non-negative fields