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Muon spin relaxation and neutron diffraction investigations of quadrupolar and magnetically ordered states of YbRu2Ge2

The magnetic and quadrupolar ordered states of polycrystalline YbRu2Ge2 have been investigated using zero-field muon spin relaxation (μSR) and neutron diffraction measurements. Specific heat measurements show three successive phase transitions, with decreasing temperature from a paramagnetic to a quadrupolar state at T0 ~ 10 K, from the quadrupolar to a magnetic state at T1 ~ 6.5 K and a possible change in the magnetic ground state at T2 ~ 5.5 K. Clear evidence for the magnetic transition below 7 K (spectrum at 8 K reveals paramagnetic state) and a likely change in the magnetic structure near 5.8 K is observed in the zero-field μSR measurements. The μSR data, however, do not reveal any signature of magnetic order in the temperature range 8 - 45 K. This result is further supported by neutron diffraction measurements, where clear magnetic Bragg peaks have been observed below 8 K, but not above it. Below 8 K, the magnetic Bragg peaks can be characterized by an incommensurate antiferromagnetic ordering with the propagation vector q = [0.352, 0, 0] and the magnetic moment 2.9(3) μB of Yb along the b-axis. These results are discussed in terms of quadrupolar ordered and magnetically ordered states.