Magnetic ordering induced by hydrogen doping of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$

Superconducting ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ samples doped with hydrogen were investigated by the muon-spin-rotation technique. For a hygrogen concentration larger than 0.5 per formula unit, we find a well-defined precession signal in zero external field. This is a clear indication of magnetic ordering in these samples. The precession frequency of 2 MHz is distinctly different from the 4-MHz signal observed in magnetically ordered oxygen deficient ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_6$ and thus excludes that the effect is due to oxygen removal from the sample. The data are consistent with the assumption that hydrogen acts as an electron donor filling the hole states in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$.