No abstract

X-ray resonant magnetic scattering has been used to examine the magnetic interactions coupling the rare earth and iron sublattices in the antiferromagnetic compound DyFe 4 Al 8 . Dramatic differences are observed in the temperature dependencies of the energy profiles at resonance depending on whether the photon energy is tuned to the Dy L 2 or L 3 absorption edge. In particular, for temperatures increasing from 10 K, the resonant scattering intensity at the L 3 edge decreases whereas that at the L 2 edge rises. We suggest a physical model capable of reproducing these phenomena. [S0031-9007(99)08671-8] PACS numbers: 75.25. + z, 75.30.MbThe 4f electrons of the rare-earth elements are well shielded from their environment so that the interactions among them take place mainly through their coupling to the 5d electrons, which form the major constituent of the conduction-electron band [1]. Interesting properties are found when the rare earths are combined in compounds, multilayers, or amorphous melts with 3d-transition elements. Broadly speaking, the 3d elements tend to give rise to a higher magnetic-ordering temperature, whereas the rare-earth elements introduce magnetic anisotropy. The magnetic nature of the rare-earth 5d states is crucial to an understanding of this class of materials. In this Letter, we report results of resonant magnetic x-ray scattering (XRES) experiments on a single crystal of DyFe 4 Al 8 that give new insight into how the 5d conduction band is affected on cooling below the Néel temperature T N , first by the ordering of the Fe 3d electrons, and then by the subsequent growth of the ordered component of the Dy 4f moments. The experiments were performed by monitoring the intensity and energy dependence of the resonant magnetic scattering for incident photon energies tuned near the Dy L 2 and L 3 edges as a function of temperature.The compound DyFe 4 Al 8 crystallizes with the bodycentered tetragonal ThMn 12 structure [see Fig. 1(a)], with a b 8.74 Å, and c 5.036 Å. Neutron-diffraction experiments [2] have shown that the single crystal used in our investigation has ordered Fe and Al sublattices. Whereas the Dy atoms contribute to all Bragg reflections, the lower symmetry of the Fe atomic sites imposes more restrictive diffraction conditions, allowing the contributions of the Dy and Fe sublattices to be separated [3]. Much work has been done on the ordered MFe 4 Al 8 compounds (M rare earth or actinide). Early studies [4] showed that antiferromagnetic (AF) ordering occurred between 140 and 180 K depending on the atom species. Our neutron experiments [2] show that the Fe sublattice orders with the moments in the (001) plane at T N ϳ 170 K in a small modification of the G-type AF structure [5]. Superimposed on the AF order, shown in Fig. 1(a), is a long-wavelength modulation with q ͓qq0͔, where q ϳ 0.14 reciprocal lattice units (rlu) at T N and locks to q 0.1333 2 15 rlu below ϳ100 K. At a lower temperature, which we define as T Dy ͑ϳ50 K͒, the intensities of the neutron reflections start to change ind...

No abstract

No abstract

No abstract