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according to the models of explosive nucleosynthesis , much of the iron comes from type ia supernovae , while @xmath4 elements such as o and mg come from type ii supernovae . because the difference in lifetime of the progenitors , it is generally considered that the iron enrichment delays relative to @xmath4 elements by 12 billion years ( @xcite ; @xcite , 1998 ) . if feii / mgii , the relative strengths of feii emission lines and the mgii @xmath2 doublet , reflects the fe / mg abundance ratio , there will be a break in feii / mgii at high redshift . despite of much efforts made by many observational groups ( e.g. , @xcite ; @xcite ; @xcite , 2003 ; @xcite , 2004 ; @xcite ; @xcite ; @xcite ; @xcite , 2008a ; @xcite ) , there have been found no signs of such a break ; feii / mgii looks constant from low - redshift up to @xmath5 with large scatter . no break in feii / mgii might reflect a significantly shorter delay - time of 0.2@xmath10.6 gyr , as suggested by @xcite , @xcite , and @xcite . the expected break can also be obscured by non - abundance effects . simulations of feii emitting regions , assuming either photoionization or shocks , imply that the fe abundance is not only one parameter which controls the feii strength , but several non - abundance factors can also affect it . such non - abundance factors include spectral energy distribution ( sed ) of the central source , strength of the radiation field , and the gas density of broad emission line region ( belr ) clouds . recently , @xcite and @xcite pointed out that a large microturbulence velocity may be responsible for strong feii emission . @xcite have studied non - abundance factors by using spectra of a low - redshift sample of 14 quasars , covering wide rest - wavlengths 1000@xmath17300  , and claimed that the feii strength correlates with the mass of the central black hole , the line width , and the x - ray photon index .    in this paper , we present spectra of six quasars at @xmath6 , and compare with those in the low - redshift sample . throughout this paper , a cosmology with @xmath7 , and @xmath8 is assumed . six quasars were selected for optical spectroscopy from the catalog by @xcite . according to the catalog , these are luminous with @xmath9 @xmath10 at @xmath11  @xmath12 , bright enough to take optical feii emission lines through near - infrared spectroscopy at a later opportunity . gmos on gemini - south telescope are used in the long - slit mode with grating r150_g5326 and order sorting filter og515_g0330 . wavelengths observed are in 5400@xmath19800  , corresponding to rest wavelengths 1800@xmath13300   at @xmath6 quasars . the slit width is 1.0  and the spectral resolution is 3.286    pixel@xmath13 . the grating was centered at 8150   for the first three exposures and changed to 8250    for the following exposures , filling up the gaps of the ccd chip array . wavelengths were calibrated using the cuar arc lamp taken at the both central wavelengths of the grating . ltt1788 ( @xcite ) was used for flux - scaling . the observing log is summarlized in table [ tab : obslog ] . individual spectral frames were processed using the gemini iraf package ver1.9.1 . sky of individual frames is subtracted with gsskysub , and then scombine was used to combine into the final spectral frame . the corrections for telluric absorption were not applied . reduced spectra are shown in figure [ fig : spec ] . redshifts are determined from fit of mgii emission line . with these measured redshifts , absolute @xmath14 magnitudes are calculated assuming a cosmology with @xmath7 , and @xmath8 . redshifts and absolute @xmath14 magnitudes are also listed in table [ tab : obslog ] .        [ cols="<,^,^,^,^,^,^,^ " , ] in table [ tab : measure ] , the feii emission line flux _ feii_@xmath15 , the mgii line flux _ mgii(total ) _ , the fwhm ( mgii ) , the 3000   luminosity @xmath16 , and the blackhole mass @xmath17 derived from equation ( [ eq : mclure ] ) , are given . note that , for b0226 - 104 , mgii emission line is heavily affected by telluric absorption line , so that we did not measure mgii flux and mgii fwhm . a plot of _ feii_@xmath15/_mgii(total ) _ against @xmath17 is given in figure [ fig : femg]@xmath18 and 3000   luminosity @xmath16 in figure [ fig : femg]@xmath19 . analyzing 14 low - redshift quasars , @xcite found the correlation between the flux ratio feii(uv)/mgii and the blackhole mass . this relation is shown by the dotted line in figure [ fig : femg]@xmath18 . filled circles are our quasars at @xmath20 and open circles are low - redshift quasars at @xmath3 by @xcite . our quasars have an absolute luminosity of @xmath21 , which are much luminous than the low - redshift quasars having an absolute luminosity of @xmath22 . as can be seen in figure [ fig : femg]@xmath18 , the five @xmath0 quasars do not follow the correlation found by @xcite . all of them have feii(uv)/mgii greater than expected from the tsuzuki s correlation . what is the cause of the large feii(uv)/mgii value in the @xmath0 quasars relative to the low - redshift quasars ? because the five @xmath0 quasars are much luminous than the 14 low - redshift quasars , the luminosity effect is examined . as shown in figure [ fig : femg]@xmath19 , the luminosity effect is not responsible for the large feii(uv)/mgii value in the @xmath0 quasars . the _ real _ cause would be evolution in feii(uv)/mgii or non - abundance effects such as the sepectral energy distribution of the continuum from the central source , the strength of the radiation field and the gas density of blr clouds as well as the microturbulence of blr gas ( @xcite ; @xcite ) . further investigations are required using large samples of quasars . this work was financially supported in part by grant - in - aid for scientific research ( 17104002 ) and specially promoted reserch ( 20001003 ) and the japan - australia research cooperative program from jsps . baldwin , j. a. , ferland , g. j. , korista , k. t. , hamann , f. , & lacluyz , a. 2004 , apj , 615 , 610 dietrich , m. , hamann , f. , appenzeller , i. , & vestergaard , m. 2003 , apj , 596 , 817 dietrich , m. , appenzeller , i. , vestergaard , m. , & wagner , s. j. 2002 , apj , 564 , 581 elston , r. , thompson , k. l. , & hill , g. j. 1994 , nature , 367 , 250 freudling , w. , corbin , m. r. , & korista , k. t. 2003 , apj , 587 , l67 friaa , a. c. s. , & terlevich , r. j. 1998 , mnras , 298 , 399 granato , g. l. , de zotti , g. , silva , l. , bressan , a. , & danese , l. 2004 , apj , 600 , 580 hamann , f. , & ferland , g. 1993 , apj , 418 , 11 hamuy , m. , suntzeff , n. b. , heathcote , s. r. , walker , a. r. , gigoux , p. , & phillips , m. m. 1994 , pasp , 106 , 566 iwamuro , f. , kimura , m. , eto , s. , maihara , t. , motohara , k. , yoshii , y. , & doi , m. 2004 , apj , 614 , 69 iwamuro , f. , motohara , k. , maihara , t. , kimura , m. , yoshii , y. , & doi , m. 2002 , apj , 565 , 63 kawara , k. , murayama , t. , taniguchi , y. , & arimoto , n. 1996 , apj , 470 , l85 kurk , j. d. , et al . 2007 , apj , 669 , 32 maiolino , r. , juarez , y. , mujica , r. , nagar , n. m. , & oliva , e. 2003 , apj , 596 , l155 matsuoka , y. , kawara , k. , & oyabu , s. 2008a , apj , 673 , 62 matsuoka , y. , oyabu , s. , tsuzuki , y. , & kawara , k. 2007 , apj , 663 , 781 matteucci , f. , & recchi , s. 2001 , apj , 558 , 351 mclure , r. j. , & jarvis , m. j. 2002 , mnras , 337 , 109 pei , y. c. 1992 , apj , 395 , 130 schlegel , d. j. , finkbeiner , d. p. , & davis , m. 1998 , apj , 500 , 525 tsuzuki , y. , kawara , k. , yoshii , y. , oyabu , s. , tanab , t. , & matsuoka , y. 2006 , apj , 650 , 57 verner , e. , bruhweiler , f. , verner , d. , johansson , s. , & gull , t. 2003 , apj , 592 , l59 vron - cetty , m .- , & vron , p. 2003 , a&a , 412 , 399 yoshii , y. , tsujimoto , t. , & kawara , k. 1998 , apj , 507 , l113 yoshii , y. , tsujimoto , t. , & nomoto , k. 1996 , apj , 462 , 266
we present spectra of six luminous quasars at @xmath0 , covering rest wavelengths 1600@xmath13200  . 
 the fluxes of the uv feii emission lines and mgii @xmath2 doublet , the line widths of mgii , and the 3000   luminosity were obtained from the spectra . 
 these quantities were compared with those of low - redshift quasars at @xmath3 studied by tsuzuki et al . in a plot of 
 the feii(uv)/mgii flux ratio as a function of the cental black hole mass , feii(uv)/mgii in our @xmath0 quasars is systematically greater than in the low - redshift quasars . 
 we confermed that luminosity is not responsible for this excess . 
 it is unclear whether this excess is caused by rich fe abundance at @xmath0 over low - redshift or by non - abundance effects such as high gas density , strong radiation field , and high microturbulent velocity . 
 galaxies : abundances  galaxies : active  line : formation  quasars : emission lines