EFFECTS OF HIGH-ENERGY HEAVY-ION BOMBARDMENT ON THE ELECTRICAL-CONDUCTIVITY OF YTTRIUM-IRON-GARNET

Epilayers of yttrium iron garnet Y3Fe5O12 on a (111)-Gd3Ga5O12 substrate were irradiated with 50 MeV S-32, 50 MeV Cu-63, and 235 MeV Kr-84 ion beams. Film thicknesses were always smaller than the mean projected ranges of the incoming ions to avoid implantation effects in the layers. Dc-resistivity and saturation magnetization of ion-bombarded films were then measured at room temperature as a function of ion fluence ranging between 10(11) and 10(16) ions cm-2. Resistivity was found to decrease when fluence is increased above a threshold (less-than-or-equal-to 10(13) ions cm-2). The threshold fluence increases as the ion energy loss is reduced. Kr-84 resistivity data level off above 3 x 10(12) ions cm-2 after a two-order-of-magnitude decrease, whereas Cu-63 and S-32 data decrease by seven orders of magnitude according to a nearly parabolic law versus fluence without any saturation up to 10(16) ions cm-2. The saturation of damage observed with Kr-84 bombardment is interpreted by the overlap of paramagnetic disordered track cores, while in the case of Cu-63 and S-32 bombardment, such a picture is not valid. These two different behaviours might be interpreted by a change in the morphology of the extended defects produced by electronic excitations above a threshold of electronic stopping power.