The production of Sr hexaferrite thick films by screen printing

Hydrothermally synthesised Sr hexaferrite (HT-SrM) powder with a distinct plate-like shape and conventional Sr hexaferrite (c-SrM) powder were used to screen print SrM thick films on alumina substrates. In the case of the HT-SrM thick films, a very strong perpendicular magnetic anisotropy has been observed with remanence values of up to 42 +/- 2 J/T kg for the perpendicular direction and 15 +/- 1 J/T kg for the in-plane direction, and with coercivities of around 159 +/- 8 kA/m for both directions when fired at 1300degreesC. When fired at 1150degreesC, the remanences were 49 +/- 2 and 27 +/- 2 J/T kg for the two directions with a higher coercivity of 247 +/- 8 kA/m for both directions. The SEM micrographs showed that the platelet grains in the printed films lay with their flat surfaces on the substrate and XRD results revealed that the c-axis of the grains oriented perpendicularly to the film surface. The (0 0 8) plane, which is, for a random oriented sample, a very weak peak, appeared as the strongest in the XRD pattern for the films. EDX and XRD studies indicated significant reaction at the interfaces between the film and the substrate when the sintering temperature was raised to 1350degreesC. For the SrM thick films obtained from planetary milled ultrafine Sr hexaferrite and conventional Sr hexaferrite powder, a slight in-plane anisotropy could be observed with a coercivity of 318 +/- 8 kA/m. (C) 2002 Elsevier Science B.V. All rights reserved.