Special Romp session, LT25 8th Aug. 2008, Amsterdam 75As-NMR study of BaFe2As2 H. Fukazawa1, N. Takeshita2, T. Yamazaki1, K. Kondo1, K. Hirayama1, Y. Kohori1, K. Miyazawa2,3, H. Kito2, H. Eisaki2, and A. Iyo2 1Department of Physics, Chiba University, Chiba, Japan 2Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan 3Department of Applied Electronics, Tokyo University of Science, Noda H. Fukazawa et al.: to be published in J. Phys. Soc. Jpn. (2008). ; arXiv:0806.4514v3. Pressure study; arXiv:0808.0718v1. 1. Magnetic order in BaFe2As2 2. Pressure effect on BaFe2As2

Discovery of superconductivity Next parent compounds As Fe Ba(K) O(F) As Fe La FeAs layer FeAs layer Y. Kamihara et al.: J. Am. Chem. Soc. 130 (2008) 3296. M. Rotter et al.: arXiv:0805.4630v1.

P induced superconductivity ?? P. L. Alireza et al.: arXiv.0807.1896. M. S. Trikachivili et al.: arXiv.0807.0616v1. P induced superconductivity ??

75As NMR spectrum of BaFe2As2 Typical powder-pattern spectrum expected for weak electric quadrupole interaction Estimated 75As NQR frequency nQ = 2.2 MHz: much smaller than nQ’s of superconducting oxypnictides (nQ ~ 9-12 MHz) H.-J. Grafe et al.: PRL 101 (2008) 047003. H. Mukuda et al.: arXiv:0806.3238v1. Partial orientation of powders: Hext parallel to ab plane G. C. Carter et al.: Metallic Shifts in NMR (Pergamon Press, Oxford etc., 1977) Chap. 2&6.

75As NMR spectra at various T Spectral broadening below 130 K SDW magnetic ordering (TSDW = 131 K in our samples) Much oriented powder: sharper Mag. easy axis: within ab plane Hint // c axis Hint Q. Huang et al.: arXiv:0806.2776v1.

FWHM & FWQM vs T 4.2 K < T < TSDW FWHM: nearly T independent FWQM: gradual decrease T ~ TSDW FWHM&FWQM: sudden decrease from finite DB to 0 T The SDW anomaly in BaFe2As2 is likely of the first order.

Zero external field 75As NMR spectrum Hint ・Hint at the As site is about 1.4 T. ・The magnetically ordered state is formed with the commensurate q vector. (consistent with q =(1,0,1) in ND) Hint Q. Huang et al.: arXiv:0806.2776v1.

Pressure effect on BaFe2As2 SDW anomaly is suppressed by applied P, but is simultaneously robust against P. P induced SC in BaFe2As2 ?? -no zero resistivity-

Pressure effect on oxypnictides/pnictides Mini cubic anvil apparatus Bridgman anvil cell 63Cu NQR - Cu2O - See also r (P,T ) of NdFeAsO0.6 N. Takeshita et al.: JPSJ 77 (2008) 075003. H. Fukazawa et al. : RSI 78 (2007) 015106. K. Hirayama et al. : JPSJ 77 (2008) 075001. Not only doping study but also pressure study of the pnictides has a strong impact upon this study field. We can perform NMR/NQR under such high pressure of 10 GPa!