No abstract

No abstract

We report element-specific magnetic hysteresis measurements on heteromagnetic materials. Dramatically different Fe and Co hysteresis curves of Fe/Cu/Co trilayers were obtained by recording the magnetic circular dichroism at their respective L3 white lines as a function of applied magnetic field. The data resolve the complicated hysteresis curves, observed by conventional magnetometry, and determine the individual magnetic moments for the Fe and Co layers. Fine hysteresis features, imperceptible in the conventional curves, were also observed, demonstrating a new and powerful means for studying heteromagnetic multilayer systems.

Polarization-dependent near-edge x-ray absorption spectroscopy measurements have been performed on the O 1s and Ni 2 p edges of La 2Ϫx Sr x NiO 4ϩ␦ single crystals for 0рxр0.6. The results are compared with recent data on La 2Ϫx Sr x CuO 4ϩ␦ , and NiO and with detailed cluster calculations on a NiO 6 cluster. From this, we determine the energetic ordering of the states close to the Fermi level with Ni͑Cu͒ 3d x 2 Ϫy 2/O 2p x,y and Ni͑Cu͒ 3d 3z 2 Ϫr 2/apex-O 2p z orbital character for the undoped compounds. We find that d-d exciton side bands show up in the final states of La 2Ϫx Sr x NiO 4ϩ␦ , giving evidence for the Zhang-Rice character of the doped carriers. The spectral-weight transfer in the O 1s spectra shows a significant dynamical component. Thus, we suggest that the polarons in La 2Ϫx Sr x NiO 4ϩ␦ can be seen as nonclassical objects on the length scale of a lattice constant and that the formation of polaron domain walls and polaron lattices possibly has to be considered as a result of this large coherence length of the polarons.

Synchrotron radiation is used to excite Ar to the intermediate states 3p 1/2 5 ͑3dЈ͓3 / 2͔ 1 , 5dЈ͓3 / 2͔ 1 , 5sЈ͓1 / 2͔ 1 , 7sЈ͓1 / 2͔ 1 ͒ and 3p 3/2 5 ͑6d͓1 / 2͔ 1 , 6d͓3 / 2͔ 1 , 8s͓3 / 2͔ 1 ͒, then excited by lasers to the autoionizing Rydberg series 3p 1/2 5 npЈ ͓͑1 / 2͔ 0,1 , ͓3 / 2͔ 1,2 ͒ and nfЈ͓5 / 2͔ 2. For the intermediate states of 5sЈ, 7sЈ, and 8s, the npЈ ͓͑1 / 2͔ 0 and ͓3 / 2͔ 2 ͒ series are observed with high intensity but not the npЈ ͓͑1 / 2͔ 1 and ͓3 / 2͔ 1 ͒ series when the polarization vectors of two light beams are in parallel; but when they are in orthogonal, the npЈ͓1 / 2͔ 0 series disappears, the npЈ͓3 / 2͔ 2 intensity remains, and the npЈ ͓͑1 / 2͔ 1 and ͓3 / 2͔ 1 ͒ series show up strongly. The intensity distribution of the npЈ series strongly depends on the intermediate state. The spectra of the npЈ series are assigned according to their intensity variation with the polarization vectors. The quantum defects determined for the series npЈ͓1 / 2͔ 0 ͑n =11-57͒, npЈ͓3 / 2͔ 2 ͑n =11-65͒, npЈ͓3 / 2͔ 1 ͑n =11-31͒, and nfЈ͓5 / 2͔ 2 ͑n =9-74͒ are 1.611Ϯ 0.011, 1.683Ϯ 0.013, 1.688Ϯ 0.010, and 0.016Ϯ 0.005, respectively. Our values are in excellent agreement with theoretical prediction. The spectral line shapes of autoionizing Rydberg states are analyzed with a Beutler-Fano profile. Reduced autoionization linewidths for the npЈ͓1 / 2͔ 0 ͑n =11-16͒ series vary in the range 2549-4145 cm −1 , and the nfЈ͓5 / 2͔ 2 ͑n =9-11͒ series in 186-247 cm −1 in reasonable agreement with theoretical prediction.