Field-Induced Commensurate Intermediate Phases in Helimagnet (Ba_{<i>1-<i>x</i></i>}Sr_{<i><i>x</i></i>})_<b>2</b>Zn_<b>2</b>Fe_<b>12</b>O_<b>22</b>(<i><i>x</i><b>=0.748</b></i>)

Abstract

Neutron diffraction and magnetization measurements have been made on single crystal specimens of hexagonal-ferrite helimagnet (Ba 1- x Sr x ) 2 Zn 2 Fe 12 O 22 ( x =0.748) in a field applied perpendicular to the c -axis. Two types of intermediate phases, intermediate-I and -II, are successively induced by a field, and their magnetic structures are determined by using the Fourier series expansion method. In each phase, the moments order in fanlike oscillatory structures in which there are large and small spin-bunches perpendicular to the c -axis. The magnetization curve and the turn angle of the helix are discussed from exchange interactions.