Pinning of 180° Bloch walls at etched nuclear tracks in LPE-grown iron garnet films

Abstract

For increasing the magnetic-wall coercivity Hwc in liquid-phase epitaxial (LPE) ferrimagnetic garnet films of composition (Gd,Bi)3(Fe,Al,Ga)5O12, magnetic-wall ’’traps’’ are formed via bombardment by xenon ions with 180-MeV/ion energy and doses between 106 and 108 cm−2. For efficient wall pinning, the width of the nuclear damage tracks associated with the ion trajectories in the film have been enlarged to about the wall width by using a selective (chemical) etchant that makes use of the drastically increased etching rate in the damaged track volume. Therefore, channels of cylindrical or prismatic cross section are created having a width of a few 102 to about 103 Å and a length of more than 10 μm at the given etching conditions. The pinning capability of such channels can be further enhanced in films that are grown under planar compressive or tensile misfit strain. Then, strain relaxation occurs in the vicinity of these channels which results in steep gradients of the magnetic-wall energy via magnetostriction. These strain halos extend sufficiently beyond the channels so that efficient wall pinning is observed, even if the channel cross section is small compared with the wall width. Thermomagnetic compensation-point writing in LPE garnet film, that were treated accordingly, yield a pattern of stable magnetic domains of down to 8 μm in diameter in 3-μm-thick layers. The effect of etched nuclear tracks on the magnetic-wall coercivity can be interpreted satisfactorily with present models on Hwc.