This dissertation has investigated the sintering and the magnetic behaviour of Gd-ZnO
bulk samples with different Gd concentrations varying from 0 to 1 at.%. The films
were deposited using the pulsed laser deposition technique (PLD). This study set out
to determine whether Gd-ZnO thin films displayed ferromagnetic behaviour above
room temperature using a SQUID magnetometer. However, a problem occurred
during the preparation of the PLD targets containing different Gd concentrations. In
fact, since the required density for the PLD targets should be more than 90%, the first
sets of targets were not sufficiently dense to be utilized in the PLD deposition. Hence,
to solve this problem, dilatometry measurements were conducted on a new series of
samples so as to find the optimum sintering temperature in order to obtain fully dense
targets. The following conclusions can be drawn from the present study.
According to the dilatometry measurements conducted on 8 mm diameter Gd-ZnO
pellets at constant heating rate of 5 °C/min, the temperature of densification, T onset,
which is set arbitrarily to 0.5% shrinkage, increases when the Gd concentration is
increased from 0 to 1 at.%. Moreover, non-isothermal dilatometry measurement with
three heating rates of 5, 10, and 20 °C/min were carried out on Gd-ZnO bulk samples
so as to calculate the apparent activation energy (Q) using both the master sintering
curve (MSC) and Arrhenius plot of the sintering data.
The results of the magnetic measurements for Gd-ZnO thin films with different Gd
concentrations varying from 0 to 1 at.% indicates diamagnetic characteristics at both
5 and 300K; however, a film containing 1 at.% of Gd indicated a super-paramagnetic-like
behaviour at 5 K but a saturated magnetization at 300 K. This superparamagnetic
behaviour may originate from the formation of the secondary phases during film
deposition.
Key words: Gd-ZnO pellets; Sintering behaviour; Arrhenius plot; Master Sintering
curve; Magnetic behaviour.