Controlling the magnetic structure in W-type hexaferrites.

W-type hexaferrites with varied Co/Zn ratios were synthesized and the magnetic order was investigated using neutron powder diffraction. In SrCo 2 Fe 16 O 27 and SrCoZnFe 16 O 27 a planar ( Cm ' cm ') magnetic ordering was found, rather than the uniaxial ordering ( P 6 3 / mm ' c ') found in SrZn 2 Fe 16 O 27 which is common in most W-type hexaferrites. In all three studied samples, non-collinear terms were present in the magnetic ordering. One of the non-collinear terms is common to the planar ordering in SrCoZnFe 16 O 27 and uniaxial ordering in SrZn 2 Fe 16 O 27 , which could be a sign of an imminent transition in the magnetic structure. The thermomagnetic measurements revealed magnetic transitions at 520 and 360 K for SrCo 2 Fe 16 O 27 and SrCoZnFe 16 O 27 , and Curie temperatures of 780 and 680 K, respectively, while SrZn 2 Fe 16 O 27 showed no transition but a Curie temperature at 590 K. This leads to the conclusion that the magnetic transition can be adjusted by fine-tuning the Co/Zn stoichiometry in the sample.