Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2011-06-03
J. Phys.: Condens. Matter 24 (2012) 135602
Physics
Condensed Matter
Strongly Correlated Electrons
10 (+) pages, 11 figures, Accepted in Journal of Physics condensed Matter
Scientific paper
10.1088/0953-8984/24/13/135602
A detailed $^{31}$P (I=1/2) and $^{75}$As (I=3/2) NMR study on polycrystalline CeFeAs$_{1-x}$P$_{x}$O alloys is presented. The magnetism of CeFeAsO changes drastically upon P substitution on the As site. CeFePO is a heavy fermion system without long range order whereas CeFeAsO exhibits a Fe-3$d$ SDW type of ordering accompanied by a structural transition from tetragonal ($TT$) to orthorhombic ($OT$) structure. Furthermore Ce-4$f^{1}$ orders antiferromagnetically (AFM) at low temperature. At the critical concentration where the Fe-magnetism is diminished the Ce-Ce interaction changes to a ferromagnetic (FM) type of ordering. Three representative samples of the CeFeAs$_{1-x}$P$_{x}$O ($x$=0.05, 0.3 and 0.9) series are systematically investigated. 1) For the $x$=0.05 alloy a drastic change of the line width at 130 K indicates the AFM-SDW type of ordering of Fe and the structural change from $TT$ to $OT$ phase. The line width roughly measures the internal field in the ordered state and the transition is most likely first order. The small and nearly constant shift for $^{31}$P and $^{75}$As suggests the presence of competing hyperfine interactions between the nuclear spins and the 4$f$ and 3$d$ ions of Ce and Fe. 2) For the $x$=0.3 alloy, evolution of the Fe-SDW type order takes place at around 70 K corroborating the results of bulk measurement and $\mu SR$. Here we found strong evidence for phase separation of paramagnetic and magnetic SDW phases. 3) In contrast to heavy fermion CeFePO for the $x$=0.9 alloy a phase transition is found at 2 K. The field-dependent NMR shift gives strong evidence of FM ordering. Above the ordering the spin lattice relaxation rate $^{31}$(1/T$_{1}$) shows unconventional, non-Korringa like behaviour which indicates a complex interplay of Kondo and FM fluctuations.
Baenitz Michael
Geibel Ch.
Jesche Anton
Sarkar Ruby
Steglich Frank
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