Thermomagnetic properties of fine-grain polycrystalline GdIG

Thermomagnetic properties of fine-grain polycrystalline GdIG were investigated in two ways. First the hysteresis loop was observed on bulk material as well as on thin wafers over the temperature range 0-70°C. The remanent flux density B
r
, the squareness ratio
B_{r}/B_{s}
, and the coercive force H
c
were found to be quite temperature dependent. The effects of stresses and grain size on the H
c
value were measured. These properties were explained in terms of domain-wall dynamics. A second set of experiments was the study of dynamic thermomagnetic laser recording on GdIG as a storage medium. The writing and reading parameters were examined. A bit diameter of 15 μm was currently written with 100-mW 1-μs pulses together with a 250-Oe bias field. Readout at rates of up to 10
⁶
bit/s was obtained for densities larger than 10
⁶
bit/in
²
. The stability of written bits was studied versus time or temperature changes and correlated with the magnetic properties.