Muons and magnets

Abstract:

We present experimental evidence for small-moment magnetism below the ferromagnetic transition temperature (Tc3=183K) in the quasi-one-dimensional metal BaIrO3. Further, we identify rearrangement of the local magnetic moment distribution, which leaves the bulk magnetization unchanged, at the Mott-like transition (Tc1=26K). These results are only possible via muon-spin relaxation (μSR) techniques, since neutron scattering studies are hindered by the large absorption of neutrons by Ir. The low-temperature characteristics of this compound, as revealed by μSR, are unconventional, and suggest that its magnetic properties are driven by changes occurring at the Fermi surface due to the formation of a charge-density wave state. © 2005 The American Physical Society.

Abstract:

We synthesized and structurally and magnetically characterized the novel 3D coordination polymer Cu(HCO2)2(pym) (pym = pyrimidine). The compound crystallizes in the monoclinic space group C2/c with a = 14.4639(8) A, b = 7.7209(4) A, c = 8.5172(5) A, beta = 126.076(2) degrees, and V= 768.76(7) A3. In the structure buckled layers of Cu(HCO2)2 are interconnected by pym ligands to afford 1D Cu-pym-Cu chains. Bulk magnetic susceptibility measurements show a broad maximum at 25 K that is indicative of short-range magnetic ordering. Between 12 and 300 K a least-squares fit of the chi(T) data to a mean-field-corrected antiferromagnetic chain model yielded excellent agreement for g = 2.224(3), J/kB = -26.9(2) K, and zJ'/kB = -1.1(3) K. Below approximately 3 K a transition to long-range magnetic ordering is observed, as suggested by a sharp and sudden decrease in chi(T). This result is corroborated by muon spin relaxation measurements that show oscillations in the muon asymmetry below T(N) = 2.802(1) K and rapidly fluctuating moments above T(N).