摘要:

In order to investigate the atomic and electronic structures of the melt‐spun metallic glass system La100−xAlx(18≤x≤45), measurements of the27Al NMR Knight shift and linewidth, as well as the magnetic susceptibility, have been carried out. The dependence of these quantities on the Al concentration shows a change in behavior atx=25, which corresponds to the equilibrium crystalline phase, La3Al, and is discussed in terms of a model previously introduced for the atomic structure. An analysis of the magnetic susceptibility indicates that thed‐electron spin/orbital contributions dominate due to a larged‐electron density of states at the Fermi energy. Values of 82 and 23 kOe per &mgr;Bofsanddspin, respectively, were obtained for the hyperfine coupling.

ISSN:0021-8979    

DOI:10.1063/1.348916

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The phosphorus nuclear spin‐lattice relaxation rate 1/T1has been measured in the quasi‐two‐dimensionalXYantiferromagnet BaNi2(PO4)2. The divergence observed just above the ordering temperatureTN&bartil; 23.6 K is analyzed within the context of the Kosterlitz–Thouless transition. For a magnetic fieldHperpendicular to theXYplane, the data presented here agree well with a recent model of freely moving vortices. The field dependence observed forHparallel suggests a drastic slowing down of the vortex velocity in that case.

ISSN:0021-8979    

DOI:10.1063/1.348816

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The recent determination of the crystal structure of PbFe12O19by means of single‐crystal x‐ray diffraction has made it possible to carry out a definitive and comparative analysis of the structure‐property relationship of PbFe12O19, SrFe12O19, and BaFe12O19. We have therefore performed57Fe Mo¨ssbauer measurements on oriented, single‐crystal, and powder samples of PbFe12O19at 298 K. For a single‐crystal oriented parallel to thecaxis, five distinct patterns are observed. The hyperfine fields, isomer shifts, and quadrupole interactions are as follows: 12k:Heff=413 kOe; &dgr;=0.33 mm s−1; &Dgr;=0.35 mm s−1; 4f1: 487 kOe; 0.24 mm s−1; 0.13 mm s−1; 4f2: 514 kOe; 0.39 mm s−1; 0.29 mm s−1; 2a: 496 kOe; 0.30 mm s−1; 0.11 mm s−1; 2b: 399 kOe; 0.30 mm s−1; 2.00 mm s−1. The relative magnitude of each of these parameters is in good agreement with and exhibits the same trend observed for high‐purity SrFe12O19. The relative intensity of the 2bpattern for the crystal oriented parallel to thecaxis is 8.2%, which approaches its theoretical value; of the total number of iron ions in the structure, 8.33% of them occupy the 2bsite. The value for the polycrystalline sample is only 5.4% of the total intensity. However, for a single crystal oriented perpendicular to thecaxis, the 2bpattern exhibits a negligible intensity within the experimental error. This result confirms the dynamic disorder in the position of the 2biron ions and suggests a stronger anisotropy for the case of PbFe12O19than for SrFe12O19and BaFe12O19. Even though the trend in hyperfine parameters at 298 K is similar to Sr, Ba, and Pb hexaferrites, PbFe12O19exhibits hyperfine fields that are consistently lower than those of the Ba and Sr analogues. This result is discussed in terms of the Curie temperatures, magnetic exchange interactions, and structural parameters. 

ISSN:0021-8979    

DOI:10.1063/1.348818

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The singlet ground state antiferromagnet RbFeBr3shows an induced moment behavior at low temperatures and orders antiferromagnetically atTN=5.5 K. A second magnetic phase transition takes place at 2.0 K. The magnetic phase between 2 K <T<5.5 K may be partially ordered while atT<2.0 K a modified triangular magnetic structure will be adopted. The temperature dependence of the magnetic excitations at the soft mode pointQ(1/3,1/3,1) show a switching of intensity at 2 K. Above 4 K the magnetic excitations start to broaden. AboveTNthe magentic excitations show a renormalization behavior. The temperature dependence of renormalization is well described by the theoretical predictions of the DCEFA model.

ISSN:0021-8979    

DOI:10.1063/1.348819

出版商:AIP    

年代:1991

数据来源: AIP