Muons and magnets

Abstract:

We report muon-spin rotation, heat capacity, magnetization, and ac magnetic susceptibility measurements of the magnetic properties of the layered spin-12 antiferromagnet NaNiO2. These show the onset of long-range magnetic order below TN=19.5K. Rapid muon depolarization, persisting from TN to about 5 K above TN, is consistent with the presence of short-range magnetic order. The temperature and frequency dependence of the ac susceptibility suggests that magnetic clusters persist above 25 K and that their volume fraction decreases with increasing temperature. A frequency dependent peak in the ac magnetic susceptibility at Tsf=3K is observed, consistent with a slowing of spin fluctuations at this temperature. A partial magnetic phase diagram is deduced. © 2005 The American Physical Society.

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.