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2. R NiC2 Ì\¢É¥«ÉdC`±­ipCGXsÀè«jCtF~gÌ 2 {ÌüúðàÂdq§xÆ´qÏÊÌ¬¬gid×§xgjª¶¶Câ»·é±ÆªmçêÄ¢é1)Bd×§xg]ÚÌTO¤ÎÛ¨¿Åé SmNiC2 ÍCRNiC2 »¨QiRÍóyÞ³fjÌÐÆÂÅéBÍ¶ßÉ RNiC2 Ì»éüú a ðàÂ\¢É¥«ÉdC`±ÉÂ¢ÄTÏ·éBRNiC2 Í Fig. 2iqÉÎµÄC2 {ÌüúðàÂdq§xÌgÆ´qÏÊÉ¦·æ¤ÈÎû»\¢ióÔQ Amm2jðÆé±ÆªiiqcÝjª¨±ÁÄ¢élqðáÆµÄ¦µÄéBñ³êÄ¢é3_5) BR ªcñ¾Zû\¢ð`¬µC»ÌÀÛÉCd×§xgÍê³âñ³Æ¢Á½á³«ðÔÉ Ni Æ C2 ªÊu·éB½­Ì RNiC2 »¨ª½­L·é¨¿É¨¢Ä©¢¾³êÄ¢éB¥«I6_14) ð¦·êûÅCSmNiC2 Í TC 17.5 K Å}ð Fig. 1 É¦·B}ÉÍCà®óÔÉàµCd×§xgÆ¥«ÆÌÔÉÈñç©Ì­¢ÖªFig. 1(a) Electron density r and an atomic chain with lattice spac­
ing a in a metallic state. (b) Modulation of the electron den­sity and periodic lattice distortion having a period of 2a in acharge­density­wave state.

êÌ­¥«]Úð¦·6)B¥CI«¿Í R 3{ ªåÉSÁFig. 2

Crystal structure of RNiC2.

20  úËõ Jan. 2010 Vol.23 No.1
(C) 2010 The Japanese Society for Synchrotron Radiation ResearchgsbNX ¡ X üñÜÉUUÉæé­¥«óyÞ»¨É¨¯éd×§xgÌ­¶ÆÁÅÌÏªFig. 3

Temperature dependences of the electrical resistivities ra, rb,and rc measured along the a, b, and c axes, respectively.

Ä¢éÆl¦çêÄ¨èCLaNiC2 ÅÍ¥C]Úð¦³¸´`±]Úð¦·15,16)B½»¿ÉÂ¢ÄdCïRÌ·xË¶«Ìªèª¨±Èíê17) C·xáºÉÎµÄ¸­

Fig. 4Temperature dependences of a satellite peak and higher har­monics along the K­direction. (a) The satellite peak charac­terized by q1 and third­order peak by 3q1. (b) Second­order{satellite peaks characterized by 2q1, denoted by 2q|
1 and 2q1.

© ç  Á É ] ¶ é Ù í ª SmNiC2 ð Ü Þ ¢ ­ Â © ÌRNiC2 É¨¢Ä©¢¾³ê½B±ÌÙíÍd×§xgÌ¶Ýð¦´µÄ¢éªCÀ±IØª±êÜÅÈ©Á½B»êéB»±ÅCäXÍúËõðp¢½ SmNiC2 P»Ì X üñÜÀ±ð¨±ÈÁ½BúËõÌPxÉªð

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ÈÁ½BX üUUÍ½Ï\¢©çÌêÉNöµÄ»ðØèoµCa ²Cb ²Cc ²ûüÌdCïR¦ ra, rb,»êCubO½ËÉä×ÄLªÁ½ã¢­xªzðàí¹Ä¨±rc Ì·xË¶«ðªèµ½B»ÌÊð Fig. 3 É¦·BÂBs¨âiq×Æ¢Á½ÃIÈiqÌêª´öÆ»ûÊÉÎ·é¾ç©ÈÙû«irarbrcjª¶Ý·éÈéêÌÙ©ÉCÔIÈäç¬ÉæÁÄà»êé½ªCT^IÈd×§xgð¦·¨¿Éä×éÆÙû«Í¬ßC]ÚÉº¤äç¬ð²×é±ÆªÅ«éB³¢Be²ÌdCïR¦ÍCT1 148 K Å¾ÄÈÜêÈ

À±ÍCSPring­8 Ì BL46XU Ì½²ñÜvðp¢Ä¨ªèð¦µ½ãC110 K tßÅÉåÆÈèC·xÌáºÉ±ÈÁ½Bâ@Éæèt¯½¿É X üi18 keVjðÎµÄÄÑ¸­·éB±ÌUé¢ÍCÈOÉñ³ê½üËµCñÜÉU­xðV`[VJE^[Å½»¿ðp¢½Ê17) Æè«IÉ¯¶Åoµ½BéBÙíÈUé¢ÍC­¥«]Ú·x TC Åà¨±èCe²ÌdCïR¦ªñ 1q¯½ËðTõµ½ÊCT1 ÈºÅih, k, l )}(0.5,sA±É¸­·é±Æª{ªèÅ¾ç}h, 0), hk0.52Éq¯½Ëª¶Ý·é±Æð©¢¾µ©ÉÈÁ½BdCïR¦Ì·xË¶«©ç TC ð©Ïàé½B±êçÌ½ËÍgxNg q1 (0.5, h, 0) ÅÁ¥ÆC~·ßöÉÎµÄ17.6(1) KC¸·ßöÅ17.8(1) KÃ¯çêéB¢­Â©Ì·xÉÎ·é q1 q¯½ËÌvÆÈèCñ0.2 K Ì¬³ÈqXeVXªÏª³ê½Bê

t@Cð Fig. 4(a)É¦·B1 Ì q1 q¯½ËÌ¼ÉC

ûCT1 ÅÍÀ±¸xàÅ¾ÄÈqXeVXªÏª³ê

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4. iqÏ²ÆtHmÌ\tg»éBÆ±ëªC­¥«]Ú·x TC ÈºÉÈéÆC·×Äé 2 i2q1j¨æÑ 3 i3q1jÌq¯½Å»êC·xðº°éÆ­xðµÈªç»ÌÊuðÏ¦Ìq¯½ËªËRÁÅ·é±Æªí©Á½BT1 É¨¯édCïRÌÙíªd×§xgÌ­¶ÉNöêûCT1 ÈãÌ·xÅÍCq1 ÉÎ·éÊuÉUU·éÌ©Û©ðØ·éÉÍCiqÏ²ª»êé©ð X

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UÍº·tßÅà¾ÄÉÏª³êC·xðº°éÆªÎC»ÌgÉÎ·éÊuÉVµ­½Ëiq¯½Ëjª·­ÈèÈªçs[N­xðå³¹CÅIIÉÍ Fig. 4

úËõ Jan. 2010 Vol.23 No.1  21

Fig. 5The diuse scattering centered at q1 observed at several tem­
peratures.

Fig. 7

Temperature dependences of (a) the value of h and (b) thehalf width at half maximum (HWHM) of the q1 satellite
peak and diuse scattering.

q1 (0.5, h, 0) Ì h Æ¼l¼iHWHMjÌ·xË¶«ð Fig. 7(a)Æ(b)É»ê¼ê¦·Bh ÌlÍ·xÉÎµÄ
A±IÉÏ»µCÈPÈªÅ\³êélÅêèÆÈéUé¢Í©çêÈ¢B±Ì±Æ©çCàÆÌ\¢ÉÎµÄ®{ÌüúðàÂ®\¢ÖÌ]ÚÍÈ­Cs®ÅéÆl¦çêéB¼l¼Íº·©ç T1 Éü©ÁÄ¸­µCT1 ÈºÅÀ±ªð\ÌÉÈé±Æ©ç·£ª`¬³êÄ¢é±Æªí©éBÈãÌ X üñÜÉUUÆdCïR¦ÌªèÊ©
çCT1 ÈºÅs®gðàÂd×§xgª­¶µC»
Fig. 6Temperature dependences of the integrated intensities of (a)the q1 satellite peak and (b) the higher­order peaks (2q1 and3q1). The inset of (a) shows the diuse scattering intensity atq1.

Ìd×§xgª­¥«]ÚÆ¯ÉÁÅµ½Æl¦é±ÆªÅ«éB5.
(a)É¦µ½ q1 q¯½ËÖÆ­B·éBtHmÉR·]ÚÉçÈ¢äç¬UUÌªèðæèLÍÍÉ¨±ÈÁ½Æ±ëCq1

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Á½BT1 æè10 K Èã¢160 K É¨¢Äi0.5, K, Lj·x T1 ÉßÃ­ÉÂêUU­xªå·é±ÆÍCÅªèµ½ X üUU­xªzÌüð Fig. 8 É¦·Bq1 ÅÌtHmÌU® v(q1 ) ª¸­·é±ÆC·ÈíSÌÆµÄ L ûüicÞûüjÉLªÁ½­xªzð¦·B¿tHmÌ\tg»ª¨±ÁÄ¢é±Æð¦´µÄ¢éBi0.5, 5.48, 0jCi0.5, 5.52, 1jCi0.5, 5.48, 2jÌÊuÉO

Ïª³ê½ 1 Ìq¯½ËÌÏª­xÌ·xË¶«ðoÌ q1 ÉÎ·éärI­¢UUª¶Ý·éB³ç

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ÉCi0.5, 5.5, 0.5jCi0.5, 5.5, 1.5jÉàã¢UU­}ü}É¦·BUU­xÍ T1 Éü©ÁÄ­UIÉxª¶Ý·é±Æªí©éB±êçÌUUÍCgxåµ q1 q¯½ËÖÆ­B·éBq1 q¯½ËÌÏª­xÍCNg qR(0.5, 0.5, 0.5jÉæè\³êéBT1 ©çA±IÉåµC80 K tßÅOaµ½ãCTC ÅËR[ÆÈéBêûCFig. 6(b)É¦·æ¤ÉC2q1 ¨æqR É­xÌSªéUUðlXÈ·xÅªèµ½ÊCgÍÏ»¹¸C­xÆ¼l¼É·xË¶«ªÑ 3q1 Ì­xÍ q1 Éä×Äá·ÅÌåªæè°Å¶Ý·é±Æªí©Á½BFig. 9(a)Æ(b)És[N­xÆéB±Ì±Æ©çCá·ÅiqÏ²Íæèé`gIÉÈÁ

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22  úËõ Jan. 2010 Vol.23 No.1·Bº·©ç T1 Éü©ÁÄ·xðº°Ä¢­Æs[N­xªåµÄ¢­±Æ©çCq1 ÌêÆ¯lÉ qR ÅàtgsbNX ¡ X üñÜÉUUÉæé­¥«óyÞ»¨É¨¯éd×§xgÌ­¶ÆÁÅÌÏªFig. 8Contour plot of x­ray diuse scattering intensity distribution in (0.5, K, L) measured at 160 K. The scale of theK­axis is enlarged in comparison with that of the L­axis for the sake of clarity.

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24  úËõ Jan. 2010 Vol.23 No.1ººWcä`måwHw¨wÈ êCutE­mail: simomuraphys.keio.ac.jpêåF¨«¨wmªðn
1992N}gåwåw@Hw¤ÈPÊæ¾ÞwBmiHw)B1992N»w¤îbÈwÁÊ¤õB1995NÖ¼w@åwm¤õB1996Ncä`måw¨wÈèC2002N¯êCutBgsbNX ¡ X üñÜÉUUÉæé­¥«óyÞ»¨É¨¯éd×§xgÌ­¶ÆÁÅÌÏªObservation of the appearance and disappearance ofa charge­density­wave in a ferromagnetic rare­earth
compound by x­ray diraction and diuse scattering
Susumu SHIMOMURA

Department of Physics, Faculty of Science and Technology, Keio University,
3_14_1 Hiyoshi, Kohoku­ku, Yokohama 223_8522, Japan

Abstract Single­crystal x­ray diraction and diuse scattering measurements of a rare­earth intermetallic
compound SmNiC2 have been performed using synchrotron radiation. A set of incommensurate satellite peaks
was found to appear below 148 K, where the resistivity exhibits an anomaly. The satellite peaks abruptly van­ish and the resistivity discontinuously decreases at a ferromagnetic transition temperature. These results canbe interpreted as the appearance and disappearance of a charge­density­wave. Future investigations on
SmNiC2 and related compounds using synchrotron radiation are discussed.

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