| Summary: | 博士 === 淡江大學 === 物理學系博士班 === 103 === This thesis reports the single crystal growth and magnetic properties of YBaCuFeO5 (YBCFO) using magnetic susceptibility and neutron diffraction techniques. Using the modified traveling solvent floating zone (TSFZ) technique, we are able to grow the high quality and sizable single crystal of YBCFO for the further studies. The crystal displayes two antiferromagnetic transitions at TN1 ~455 K and TN2 ~ 170 K as indicated by the spin susceptibility anomalies. Using single crystal neutron diffraction measurement, the antiferromagnetic phase between 170 and 455 K is revealed to be a commensurate phase with a q-wavevector qN1=(1/2 1/2 1/2), and this phase undergoes a phase transition to form an incommensurate phase with a q-wavvector qN2=(1/2 1/2 1/2±δ) at TN2, where the incommensurabity δ is dependent on temperature. Further, using high resolution neutron powder diffraction, the incommensurate magnetic phase is confirmed to be a spiral magnetic phase in which the magnetic moments of Fe and Cu ions are laid on the ab-plane to be consistent to that observed by the magnetic susceptibility measurement result.
A detailed H-T phase diagram has been mapped for the YBCFO. By sweeping the temperature and magnetic fields perpendicular to the c-axis, an irreversible commensurate-incommensurate phase crossover with intermediate metastable phases are observed.
This thesis also reports the study of the nonstoichiometry effect of Cu and Fe in YBa(Cu1-xFex)2O5 system. Both of the transition temperatures TN1 and TN2 are sensitively varied from the Cu:Fe=1:1 ratio as little as 1%, which explains the inconsistency of TN1 and TN2 as reported in literatures.
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