Ferromagnetic Hollandite K2Cr8O16

The magnetism of a quasi-one-dimensional ferromagnetic (FM) compound, K2Cr8O16, has been investigated by muon-spin rotation and relaxation (μ+SR) using a powder samplein the temperature range between 2 and 230K. Below TC = 164 K, muon-spin precession signals were clearly observed in the zero-field spectrum, indicating the formation of static FM order.The distribution of the internal field was found to change slightly at the metal-to-insulator transition temperature, TMI ∼ 95 K. Electrostatic potential calculations and dipole field calculations suggested that FM order is not parallel to the [001] direction but likely parallel to the [110] direction.