Complex magnetism in Ni 3 TeO 6 -type Co 3 TeO 6 and high-pressure polymorphs of Mn 3−x Co x TeO 6 solid solutions

International audienceNew Ni3TeO6-type (NTO) and double perovskite (DPv) polymorphs of Co3TeO6 are synthesised at pressures of 15 GPa. A complex elliptic helical magnetic order is observed in the NTO polymorph (TN1 = 58 K) that reorientates (42 K) and further splits (TN2 = 23.5 K) creating a coexisting helix. Increasing Co content within the Mn3-xCoxTeO6 system changes the dominant DPv phase to NTO structural type and drastically modifies the magnetic behaviour. DPv Co3TeO6 is the first A-site double cobaltite