THE SPIN TURNING IN FERROMAGNETIC GD STUDIED BY POSITIVE MUONS

We have studied the muon precession frequency in a ferromagnetic singl e crystal of Gd metal. The overall features of our findings are compat ible with earlier results on polycrystalline material. In the temperat ure region between 245 and 220 K where the Gd magnetization starts to turn away from the c-axis, we observe an increase in the muon depolari zation rate, and a complex precession signal which can be separated in to two frequency components meaning that spin turning does not occur s imultaneously in different parts of the sample (domains). From these m ore detailed data follows that previously obtained values for B(fc) an d B(dip) can not both be correct. Two explanations for our new result are possible: Either B(fc) undergoes a change around 230 K which is di rectly coupled to the spin turning angle, or the value of the dipolar field contribution used in the earlier evaluation is too low. This imp oses some uncertainty as to the value of the angle at the onset of spi n turning derived from muSR frequencies.