Antiferromagnetic Ordering Coupled with Phonon Mode Anomalies in Rare-Earth Cuprate NdCu_2O_4, Probed by Nuclear Quadrupole Resonance and Raman Spectroscopy(Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

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We found evidence that two successive antiferromagnetic orderings of a rare earth cuprate NdCu_2O_4 (nonstandard monoclinic structure with magnetic Cu(1) and nonmagnetic Cu(2) sites) are strongly coupled with phonon mode anomalies. The nuclear quadrupole resonance frequency of ^<63,65>Cu on the Cu(2) site shows a step decrease below each of the ordering temperatures T_<N1>〜20K and T_<N2>〜10K, that originates from changes in the symmetry of the charge distribution on the surrounding lattice. In the Raman spectrum, the shift of a phonon mode near 300cm^<-1> displays an anomalous temperature dependence, which suggests a hardening of the lattice below T_<N1> and a softening below T_<N2>. The Cu^<2+> spins on the Cu(1) site order antiferromagnetically below T_<N1>, and the complex magnetic behavior is ascribed to the variations in the exchange interactions between the Cu(1) spins and in the paramagnetic spin polarization of Nd^<3+> below T_<N2>.
社団法人日本物理学会の論文
2005-07-15