Magnetic studies of annealed and alloyed chromium by neutron diffraction

The onset of long-range magnetic order in a heavily crushed powder of chromium takes place at 450 °K, below which a simple antiferromagnetic structure AF 0 exists. With reduction of temperature it gradually transforms into the structure AF 1 which is incommensurate with the unit cell. The subsequent spin-flip transition (AF 1 -> AF 2 ) occupies a temperature range and is incomplete even at 4·2 °K. When the sample is annealed the AF 0 structure becomes less prominent and the temperature ranges of both the spin-flip and commensurate-incommensurate transitions decrease, until the `normal' (single-crystal type) behaviour is reached. Study of a chromium-½% rhenium sample gives an indication of the nature of the AF 0 -AF 1 transition.