Dec. 16, 2008 Pohang APCTP

Transcription

1 Dec. 16, 28 Pohang APCTP Large electric polarization in high pressure synthesized orthorhombic manganites RMnO 3 (R=Ho,Tm,Yb and Lu) by using the double-wave PE loop measurements Yisheng Chai, Y. S. Yang, J. B. Park, N. Manivannan, Y. S. Oh and Kee Hoon Kim XMPL, Department of Physics and Astronomy, Seoul National University S. M. Feng, L. J. Wang and C.. Jin Institute of Physics, Chinese Academy of Science, P.O. Box 63, Beijing, China

2 Introduction Outline Double wave method and setup P-E and P-T measurements for RMnO 3 (R=Rare earth)

3 Introduction Sawyer Tower circuit for P-E loop measurement C >>C x x = + y,, /thickness=e y = /C /area=p sine wave y x Three components for P-E loop The review of scientific instrument, 28, 3 (1957) ferroelectric capacitive resistive typical loop P P P E + E + E = Ferroelectrics, 259, 55 (21)

4 P(T) -- integrate pyroelectric current up to T c. problems: -- leakage current is large below T c P(T) -- resistivity is low or space charge effect? P-E loop P-E loop of banana, J F Scott, J. Phys.: Condens. Matter 2, 1 (28) New method is needed for samples with leakage!!!

5 P P N Double wave method (M. Fukunaga et al J. Phys. Soc. Jpn. 77, 6476 (28)) P P1 P P2 P N1 P N2 t N2 N P1 P2 discriminate hysteresis components only

6 -- 2 Hz limited E M. Fukunaga et al J. Phys. Soc. Jpn. 77, 6476 (28) Our setup -- up to1 khz higher E -- sine wave variable de/dt -- triangular constant de/dt

7 Large polarization in orthorhombic RMnO 3 Makoto Tachibana, et al PRB 75, 27 Structure of orthorhombic TmMnO 3 Phase diagram of orthorhombic RMnO 3 Double exchange origin Oxygen orbital polarization origin S. Picozzi, et al. PRL 99, (27)

8 Although the expected P 6μC/m 2 for HoMnO 3 S. Picozzi,PRL 99, (27) B. Lorenz et al. Phys. Rev. B 76, 1445, 27 found P<9 μc/m 2 in HoMnO 3 -- small value -- strongly influenced by Ho spin b Synthesize Lu, Yb, Tm and HoMnO 3 polycrystals under high pressure Systematic change of lattice parameters c / 2

9 P-E and pulse poling of P-T measurements on HoMnO 3 P P1 P2 PE loop measurement procedure P (μc/m2) HoMnO 3 1 N N1 N2 1 K T (K) P P1 N P(T) PE vs P(T) at 1 K 1 khz PE and P(T) almost match t Asymmetry of loops -1 N1-2 2 E (k/m) -1

10 P (μc/m 2 ) thermal history related Polarization in HoMnO 3 and its P-E loops HoMnO3 as grown 5 PT 4 PE 3 PT 3 PE 2 PT 2 PE 1 PT 1 PE P (μc/m 2 ) K 15K 2K 21K 22K 23K 24K 25K 26K T (K) P=255 μc/m 2 at 1K No large influence to P by Ho spin E (k/m)

11 P (μc/m 2 ) P-E and pulse poling of P-T measurements on TmMnO 3 TmMnO 3 as grown 4PT 3PE P (μc/m 2 ) 4 2 1K 15K 2K 25K 3K 32K 33K 34K T (K) -2-4 PE loops -- fully saturated above 15 K Polarization--should be near 6μC/m 2 at 1 K E (k/m)

12 P-E and pulse poling of P-T measurements on YbMnO 3 P (μc/m 2 ) YbMnO 3 as grown T (K) 1PE 1PT 4PE 5PE 5PT P (μc/m 2 ) K 15K 2K 25K 3K 32K 34K 35K slight thermal history effect P close to 7μC/m 2 at 1 K E (k/m)

13 P (μc/m 2 ) P-E and pulse poling of P-T measurements on LuMnO 3 LuMnO 3 as grown 5 PT 4 PE 1 5 P (μc/m2) 1K 15K 2K 25K 3K 32K 34K 36K 38K T (K) P = 92μC/m 2 at 1 K E (k/m)

14 Polarization and lattice parameters vs. Ion radius Lu Yb Tm 1 Ho 8 P (μc/m 2 ) PE at 1 K r R P, the difference between two kinds of Mn-O-Mn angles contradict with double exchange mechanism

15 Discussion P-E vs pulse poling P-T: --consistent in all the RMnO 3 polycrystals Asymmetry of P-E loops: --maybe due to oxygen deficiency change of P is contradicted with the double exchange origin, --may mainly come from polar charge distribution.

16 Conclusion Developed a simple double wave P-E loop measurement system Confirmed large polarization in the E-type AF phase of RMnO 3 compounds. P maybe mainly due to oxygen orbital polarization contribution.

17 Thank you