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Studies of the AC magnetic susceptibility and electrical resistivity of polycrystalline samples of ZrZn
2, synthesized at high pressure, were performed at pressures up to 4.5
GPa and temperatures down to 0.4
K. The evolution with pressure of the line of ferromagnetic phase transformations qualitatively agrees with numerous previous data, though the transition temperature is highly sensitive to the quality and history of samples. Upon approaching zero temperature, the transition line bends toward the pressure axis as dictated by the Nernst theorem. An additional feature of the phase diagram was discovered in the samples with the highest Curie temperature (25–26
K). The electrical resistance of these samples drastically decreases near 1.4–1.8
K at ambient pressure. The temperature of this resistive transition does not change much with pressure and crosses the Curie line at a pressure near 1.2
GPa, seemingly forming some sort of tetracritical point. Application of magnetic fields up to 2
T suppresses the transition that one may expect if superconductivity is involved. However, heat capacity measurements do not show any anomaly at the transition, which resembles the case described by Pfliederer et al. [Nature (2001) 58].