Alas, as others have pointed out upthread, the high-temp superconductors don't work well for magnets. All superconducting materials lose their superconductivity at a certain magnetic field-strength threshold; for high-Tc materials, that threshold is much lower than it is for "conventional" superconductors.
Even if that weren't an issue, the ceramic materials are generally too brittle to stand up to the mechanical forces inside a high-field magnet coil.
Our lab has experimented with high-Tc superconducting probes for MRI. Even though they're high-Tc, we still end up cooling them to the liquid-helium range.