Short-range magnetic order, irreversibility and giant magnetoresistance near the triple points in the (x, T) magnetic phase diagram of ZrMn6Sn6-xGax

摘要

We have studied pseudo-layered ZrMn6Sn6-xGax intermetallics (0.55 ≤ x ≤ 0.81) using magnetic, magnetoresistivity and powder neutron diffraction measurements. All the alloys studied have magnetic ordering temperatures in the 450-490 K temperature range. They present complex temperature-dependent partially disordered magnetic structures whose ferromagnetic component develops upon increasing the Ga content. ZrMn6Sn6-xGax alloys with x ≤ 0.69 are essentially collinear antiferromagnets at high-temperature and adopt antifan-like arrangements at low temperature. For x ≥ 0.75, the alloys order ferromagnetically and evolve to a fan-like structure upon cooling. The intermediate compositions (x = 0.71 and 0.73) present a canted fan-like order at high temperature and another kind of antifan-like arrangement at low temperature. The degree of short-range order tends to increase upon approaching the intermediate compositions. The (x, T) phase diagram contains two triple points (x =0.70; T～460 K and x～0.74; T～455 K), where the paramagnetic, an incommensurate and a commensurate phases meet, which possess some of the features of Lifshitz point. Irreversibilities manifest in the lowtemperature magnetization curves at the antifan-fan or fan-ferromagnetic boundaries as well as inside the fan region. Giant magnetoresistance is observed, even above room temperature.