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Kenji Ohwada,Tatsuo Fukuda,Jun’ichiro Mizuki,Kazuma Hirota,Hikaru Terauchi,Satoshi Tsutsui,Alfred Q. R. Baron,Hidehiro Ohwa,Naohiko Yasuda 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
Pb(In_(1/2)Nb_(1/2))O_3 (PIN) can be antiferroelectric (AFE), ferroelectric (FE) or a relaxor depending upon the perovskite B-site randomness. In order to clarify the effect of B-site randomness, we studied the dynamics of ordered PIN without B-site randomness (O-PIN, AFE), which will give us a clear picture of the AFE/relaxor nature of the ground state due to B-site randomness. The quasielastic (QE) scattering shows a critical slowing down near the Γ-point and the transverse acoustic (TA) mode shows a softening trend at a finite wavenumber position (not at the Γ-point) towards the AFE phase transition temperature (T_N ∼ 450 K). On the other hand, the transverse optic (TO) mode shows a softening near the Γ-point toward low temperature with no clear anomaly at T_N. These results indicate that the AFE phase transition is associated with the TA mode and the origin of the QE scattering while a ferroelectric correlation exists behind the AFE ordering. The effect of B-site randomness is finally discussed on the basis of the results.
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Hiraka, Haruhiro,Yano, Shin-ichiro,Fukuda, Tatsuo Elsevier 2019 Journal of magnetism and magnetic materials Vol.469 No.-
<P><B>Abstract</B></P> <P>Low-energy magnetic excitation of spin-density wave (SDW) was measured using a single crystal of Cr<SUB>0.99</SUB>Fe<SUB>0.01</SUB> by cold neutron triple-axis spectroscopy. Because of the unchanged incommensurate Q and the constant line width in 2.5 ⩽ ℏ ω ⩽ 6 meV, the magnetic excitation could not be explained with a conventional dispersion of ℏ <SUB> ω q </SUB> ∝ q . Here, we conjectured the presence of standing waves, which would be excited in local spin matrices. The effectively vertical dispersion was attributed to the longitudinal spin fluctuation in the spin matrices. A series of low-energy magnetic excitations in Cr alloys could be understood with the coexistence of the standing waves and progressive waves such as spin waves.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A vertical dispersion appeared in the incommensurate spin-density-wave excitations of Cr<SUB>0.99</SUB>Fe<SUB>0.01</SUB>. </LI> <LI> The dispersion could not be explained using the concept of conventional antiferromagnetic dispersion. </LI> <LI> We newly proposed the presence of possible excitations from standing waves in local spin matrices. </LI> <LI> In our model, the effectively vertical dispersion was attributed to the longitudinal spin fluctuation excited in local spin matrices. </LI> <LI> A series of low-energy magnetic excitations in Cr alloys could be understood with the coexistence of standing waves and progressive waves. </LI> </UL> </P>
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