Radiation Physics and Chemistry 61 (2001) 545–546 Spin-dependent electron momentum densities in Co 2 FeGa studied by Compton scattering Aniruddha Deb a, *,M.Itou a , Y. Sakurai a , N. Hiraoka b ,N.Sakai b a Experimental Research Division, SPring-8, Japan Synchrotron Radiation Research Institute (JASRI), 1-1-1 Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan b Department of Material Science, Himiji Institute of Technology, 1-2-3, Kamigori, Ako, Hyogo 678-1297, Japan Abstract ThespindensityofHeusleralloyCo 2 FeGa,hasbeenstudiedusingtheComptonscatteringtechniquewith274keV circularlypolarizedsynchrotronradiationinthehighenergyinelasticscatteringbeamline(BL08W),atSPring-8,Japan. The magnetic Compton profiles along the two principal directions [110] and [111] were measured. The spin profiles showsagoodagreementwithourFLAPW-GGAresults,wherethetheoreticalresultswerebasedontheferromagnetic ground state. The 3d spin moment at the Co and the Fe site was found to be in excellent agreement with the earlier reported neutron diffraction measurements. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Compton scattering; Spin density; Synchrotron radiation Heusler alloys are ternary intermetallic compounds with stoichiometric composition X 2 YZ. They either have the L2 1 ,DO 3 or B2 structure. Heusler alloys are interesting magnetic systems because they possess localized magnetic moment although they are all metallic. The Heusler alloy Co 2 FeGa, has a L2 1 structure with unit cell consisting of four interpenetrat- ing face centered cubic sublattices. The lattice constant and the saturation moment are 5.737A and 5.13 m B , respectively. The formation and the coupling of the magnetic moments in Heusler are still a subject of theoretical and experimental studies. Though many experimental and theoretical studies on the electronic structure of Heusler alloy has been reported earlier, the compound in question here ðCo 2 FeGaÞ has been only studied earlier by Buschow and Van Engen (1981) and very recently by Brown et al. (2000) using polarized neutron diffraction technique. Brown et al. (2000) obtained a small positive delocalized moment for Co 2 FeGa and Co 2 MnGe compared to the other Co- based Heusler alloys where they found the delocalized moment to be small and negative. Bearing all these considerations in mind, it seemed worthwhile to carry out a experimental and theoretical study on Co 2 FeGa. The magnetic Compton profile measurements on the Co 2 FeGa Heusler alloy was performed at the magnetic Compton spectrometer installed at the high energy inelasticscatteringbeamlineBL08WatSPring-8,Japan. The X-ray source at this beamline is an elliptic 37-pole wigglerwithacriticalphotonenergyof42.6keV,where the wiggler was operated with K x ¼ 0:6 and K y ¼ 11:2. Elliptically polarized 274keV X-ray were tuned by the assymetric Si(771) Johann-type monochomator using a Compton scattering angle of 175 1 . Ingot of Co 2 FeGa was examined using the Laue diffraction technique. Singlecrystalswerethencutfromtheingotintheform of rectangular parallelepipeds with approximate dimen- sions 8mm  7mm  7mm. The sample was mounted in an external field of 2.5T generated by a super- conducting magnet, which was sufficient to saturate the magnetization of the samples at 300K. The integrated counts for the momentum range @10a.u. to +10a.u., were equal to 7  10 6 under the Compton line in the total spectrum and 4  10 4 in the spin-dependent Compton profiles for the [110] direction, where the measurement was about 32h. Energy dependent corrections, namely the absorption *Corresponding author. Fax: +81-7915-8-0830. E-mail address: ani12@spring8.or.jp (A. Deb). 0969-806X/01/$-see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII:S0969-806X(01)00327-9