The magnetoresistance components $rho_{xx}$ and $rho_{xy}$ were measured in two p-Si/SiGe/Si quantum wells that have an anisotropic g-factor in a tilted magnetic field as a function of temperature, field and tilt angle. Activation energy measurements demonstrate the existence of a ferromagnetic-paramagnetic (F-P) transition for a sample with a hole density of $p$=2$times10^{11}$,cm$^{-2}$. This transition is due to crossing of the 0$uparrow$ and 1$downarrow$ Landau levels. However, in another sample, with $p$=7.2$times10^{10}$,cm$^{-2}$, the 0$uparrow$ and 1$downarrow$ Landau levels coincide for angles $Theta$=0-70$^{text{o}}$. Only for $Theta$ > 70$^{text{o}}$ do the levels start to diverge which, in turn, results in the energy gap opening.
Download