  The hexaferrites are known to exhibit a wide range of magnetic structures,
some of which are connected to important technological applications and display
magnetoelectric properties. We present data on the low field magnetic
structures stabilised in a Y-type hexaferrite as observed by resonant soft
X-ray diffraction. The helical spin block arrangement that is present in zero
applied magnetic field becomes fan-like as a field is applied in plane. The
propagation vectors associated with each fan structure are studied as a
function of field, and a new magnetic phase is reported. Mean field
calculations indicate this phase should stabilise close to the boundary of the
previously reported phases.
