Interwoven magnetic and flux line structures in single crystal (Tm,Er)Ni2B2C (invited)

We review studies of the interactions between magnetic order and the flux line lattice (FLL) in the (RE)Ni2B2C intermetallic borocarbides for (RE) = Tm and Er using small angle neutron scattering (SANS) and magneto-transport. For (RE) = Tm the magnetic order and the FLL assume a common symmetry, sharing a phase transition at similar to 2 kOe, despite an order of magnitude difference in periodicity. For (RE) = Er, the penetration depth lambda and the coherence length xi, both of which are derived from the FLL form factor, are modified near T-N = 6 K by a theoretically predicted weakly divergent pairbreaking. Finally, below 2.3 K, (RE) = Er shows a coexistence of weak ferromagnetism and superconductivity. This state reveals a highly disordered FLL and a striking increase in the critical current, both arising from the strong ferromagnetic pairbreaking. (C) 2000 American Institute of Physics. {[}S0021-8979(00)61908-4].