Resonant magnetic X-ray scattering studies of heavy fermion superconductors

The uranium-based heavy fermion superconductors which are known to display weak antiferromagnetism at low temperatures are well suited to study by the newly developed resonant magnetic X-ray scattering technique. We review recent synchrotron X-ray scattering studies of the magnetic behavior of UPd2Al3 and URu2Si2 and the interaction between magnetism and superconductivity in these materials. These measurements show resolution-limited magnetic Bragg peaks in UPd2Al3 in contrast to those in URu2Si2. The order parameter as measured at the (0 0 12) magnetic reciprocal lattice position in UPd2Al3 is different from that at (0, 0, 32), the latter of which indicates a strong anomaly at TNI ∼ 11.8 K below the sharp onset of the antiferromagnetic phase at TN ∼ 14.5 K. Finally, the behavior of the (0 0 12) order parameter is smooth for T ≤ Tc = 2.00 ± 0.04 K.