Magnetic susceptibility, electric resistivity and neutron diffraction measurements were carried out for the single crystals of SrFe03-Z (x 2: 0.1). Above the N k l temperature the magnetic susceptibility does not obey the Curie-Weiss law. The activation energy is 0.013 eV. SrFe0,( x -0.1) has the proper screw spin structure with the propagation vector of 0.130 x 2 n/a [Ill] at liquid helium temperature. An Fe4-I. ion has the magnetic moment of 1.6 & 0.3 pH, which means the electron configuration is close to the low-spin state (ti,). An oxygen ion has the magnetic moment of 0.3 pn antiparallel to the vector sum of the magnetic moments of two iron ions lying on the neighbouring planes perpendicular to the screw axis. The magnetic moment of the oxygen ion is considered to be due to the electron transfer in hybrid Po-e, orbitals. 1 . Introduction. SrFeO, is a cubic perovskite (u = 3.850 A) with the proper screw spin structure whose propagation vector is parallel to [I 111 direction [ l ] and shows metallic conductivity with p -~ O ~ Q . c r n [2]. I t shows n o Jahn-Teller distortion down to 4.2 K [2] against expectation if the Fe4+ ion were to take the high-spin electron configuration (tZg 3eg). The value of the isomer shift of a n ~ e ~ + ion is more positive [3, 4 ,5] than that expected for a purely ionic state [6], so that the bonding between iron and oxygen ions is considered to be covalent. In SrFe0,-,, as the oxygen deficiency becomes large, the NCel temperature is lowered from 134 K for x = 0.00 to about 80 K for x = 0.16 and conductivity decreases [2]. The internal field and the isomer shift of Fe4+ and Fe3+ ions are observed separately in the Mossbauer spectrum [4J and those of Fe3+ ions are about the same as those in other compounds, thus Fe3+ ion being considered to be in the high-spin 3 2 state (t,, e,). The single crystals of SrFe0,-, (x 0.1) were grown and the magnetic susceptibility, electric resistivity and neutron diffraction measurements were constituent compounds, SrCO, and Fe,03, in air a 1 OOOOC for about two weeks. The products were of cubic structure with the lattice constant a = 3.86 A and were identified as SrFeO, ,,, by chemical analysis. The samples were put in a crucible (Pt 80 % Rh 20 %), c a k e d out t o obtain further informations about the ,.I I, electronic structure of the Fe4+ ion and the covalencv o loo 200 300 effect with oxygen ions. T o ( ) FIG. 1. Temperature dependence of the magnetic susceptibility X, (black circle) and the reciprocal susp above the NCel temperaFIG. 4. -The proper screw spin structure of SrFe02.90~0.03 vroiected on (1 11) plane. Mi (i = 0, 1, 2, 3) is the magnetic FIG. 3. --The magnetic form factor per formula unit of moment (1.6 p ~ ) o f ~ e t atom and rn,j is the magnetic moment SrFeO~.po*o.o~ at liquid helium temperature. The dashed curve (0.3 pn) of Ott atom which is in the middle of the line connecting is the spherical form factor of Fe4+ ion. Fei and Fer atoms. 0 is 4 7 O at liquid helium temperature. SCREW SPIN STRUCTURE IN S ~ F ~ O J C1-123 ture the activation energy is E, = 0.013 eV. Moreover, the resistivity was also measured after field cooling (H = 15 kOe) from above the Nee1 temperature in order to make the sample a single magnetic domain, but no difference was recognized from the result of the non-field cooled specimen. 2 .3 NEUTRON DIFFRACTION. Neutron diffraction study was carried out by using a neutron beam of the wave length 1.049 A. The single crystal was set in such a way that the scattering vector lies in the (110) plane. The magnetic satellites were observed from two magnetic domains whose propagation vector was parallel to [I1 I ] and [I 111. The propagation vector of the proper screw spin structure was 0.130 x 2 a/a [I 111 a t liquid helium temperature, which means that the angle between the nearest neighbouring iron moments is 470. The propagation vector was constant at temperatures below 50 K, while it decreased gradually at higher temperatures, reaching 0.1 18 x 2 a/a [I11 ] at T,, which means the angle is 42O. The magnetic form factor per formula unit was obtained from the magnetic satellites at liquid helium temperature as shown in figure 3. The dashed curve is the spherical form factor of an Fe4+ ion [7]. 3. Discussion. The magnetic moment per iron ion is 2.3 p, at liquid helium temperature, as it can be seen [I] TAKEDA, T., YAMAGUCHI, Y. and WATANARE, H., J. Phys. Soc. Japan 33 (1972) 967. 121 MACCHPSNEY, J. R., SHERWOOL), R. C. and POITITER, J . F., J. Chem. Phys. 43 (1965) 1907. [3] SHIRANE, G., COX, D. E. and Runu, S. L., Phys. Rev. 125 (1962) 1158. [4] GALLAGHER, P. K., M A C C ~ S N E Y , J . B. and BUCHANAN, D. N . E., J. Chem. Phjls. 41 (1964) 2429. in figure 3. In SrFe0,.90*o,03, 80 _+ 6 percent of the total iron ions exist in the state of Fe4+ ions and the other in that of Fe3 + ions. An Fe3+ ion is considered to take the high-spin electron configuration (t,, 3ei) and have the magnetic moment of 5 p, according to the magnitude of the internal field. Thus the magnetic moment of an Fe4+ ion has been evaluated to be 1.6 f 0.3 p,, so that the electron configuration of an Fe4' ion seems to be close to the Iow-spin state (t:,). The deviation of the observed form factor from the calculated one is considerably large, especially the value of (666) at sin 0/). = 0.029 A-' which is only about 70 percent of the calculated one. The aspherical form factore [7, 81 is always smaller than the experimental error at sin 6/A < 0.4 A-' when an Fe4+ ion takes t:, electron configuration. Thus the deviation from the spherical form factor should be explained as due to the magnetic polarization of oxygen ions. As a result the oxygen ion has the unpaired electron with the magnetic moment of 0.3 p, antiparallel to the vector sum of the magnetic moments of two iron ions lying on the neighbouring planes perpendicular to the screw axis, as shown in figure 4. The magnetic moment of an oxygen ion is considered to be due to the electron transfer in the hybrid orbitals with two neighbouring iron ions. The dominant path for electron transfer is considered to be through PC-e, orbitals.