μSR studies in the heavy fermion systems UNi2Al3, UPd2Al3 and U2PtC2

We have performed Muon Spin Relaxation (μSR) measurements of several heavy fermion systems: UNi2Al3 (single crystal), UPd2Al3 (single crystal) and U2PtC2 (polycrystal). ZF -μSR measurements of UNi2Al3 show magnetic order below the Néel temperatureTN=4.6K, with the muon precession frequencyν(T → 0)=2.5MHz at low temperatures. The local field distribution obtained at low temperatures in UNi2Al3 resembles that of the incommensurate spin density wave (SDW) system (TMTSF)2PF6, suggesting an incommensurate spin arrangement in UNi2Al3. TF -μSR measurements give the penetration depthλ(T → 0)=6100Å for UPd2Al3 andλ(T→ 0)=7000Å for U2PtC2 respectively. Since UPd2Al3 and U2PtC2 are clean superconductors (ζ/l-0), we can combineσ∝ ns/m* with the Sommerfeld constantγ ∝ ns1/3m* to calculate the Fermi temperatureTF ∝ σ3/4γ−1/4, which represents the characteristic energy scale of the superconducting carriers. We obtainTC/TF ≈ 0.01 for both UPd2Al3 and U2PtC2, comparable to other exotic superconductors, but quite different from simple metal BCS superconductors, whereTC/TF ≤ 0.01.