摘要:

An experimental study of the temperature dependence of the spin density asymmetry parameter &ggr; in a ferromagnetic iron single crystal has been made with polarized neutrons. We find no change in &ggr; as the temperature is increased up to 650°C contrary to the predictions of the simple rigid band model. Beyond this temperature the experimental errors are larger and &ggr; harder to assess. Still, a structure is indicated which could be associated with the depopulation of a Van Hove singularity in the majority spin band as it passes the Fermi energy.

ISSN:0094-243X    

DOI:10.1063/1.2953882

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The pseudo‐binary solid solution systemGd1−xThxFe3has been investigated with respect to magnetic properties. All members of the system exhibit thePuNi3‐type structure. The magnetic behavior of materials in the composition rangex = 0to aboutx = .5can be understood in terms of a collinear two‐sublattice model in which the total gadolinium moment is alligned antiparallel to the total iron moment. Such a model has been found to be applicable to nearly all known rare‐earth transition metal ferrimagnets. For the composition rangex > .5 (x = 1 excluded(, however, there is evidence for the existence of a non‐collinear state at low field strengths (< 10 kOe) below room temperature. &sgr;(t) curves show an abrupt transition; the temperature and magnitude of which vary with composition and applied field. &sgr;(H) curves at various temperatures up to the transition point show a pronounced step at about 11 kOe. The magnetic behavior of ThFe3is that of a typical ferromagnet withTc = 450°K.

ISSN:0094-243X    

DOI:10.1063/1.2953883

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The (100) vacuum cleavedNiOsurface has been examined by low energy electron diffraction and Auger electron spectroscopy. Half‐order diffraction features were observed, of the type reported by Palmberg et al, and the possibility that they result from impurity ordering is precluded. It is found, in fact, that they are observable only from an exceptionally clean surface. It is concluded that these features probably result from exchange scattering. The consequences of the observations of surface contamination for work on exchange coupled systems are discussed.

ISSN:0094-243X    

DOI:10.1063/1.2953884

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Neutron diffraction measurements on single crystals of154Sm have been performed to determine the magnetic structure and magnetic form factor. The Sm crystal structure consists of a nine layer stacking sequence along the c‐axis with 2/3 of the sites having local hexagonal symmetry and 1/3 having local cubic symmetry. The hexagonal sites order at 106°K in an antiferromagnetic layer‐type structure with a stacking sequence (++0−−0…) along the c‐axis. The zeroes correspond to layers of cubic symmetry and the hexagonal moments are directed along the c‐axis. The magnetic cell is twice the chemical cell in the c‐direction. At 14°K, the cubic sites order in ferromagnetic layers parallel to (101) planes. Considering only the cubic sites, there is a (++−−) sequence along a direction perpendicular to these planes with moments parallel to the c‐axis. The magnetic cell for the cubic‐site structure is four times the chemical cell along both a‐ and c‐directions. No modification of the hexagonal‐site structure is observed when the cubic sites order. An unusual form factor is expected because of partial cancellation of orbital and spin moment in Sm+3. Preliminary form‐factor measurements for the cubic sites show a net moment per atom close to zero with a maximum in the form factor at aboutsin&THgr;/&lgr; = 0.40.

ISSN:0094-243X    

DOI:10.1063/1.2953885

出版商:AIP    

年代:1972

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.2953886

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The effect of magnetic fields on the conical moment structure of erbium has been investigated by neutron diffraction at NBSR. The basic periodicity of the magnetic structure&tgr; = .24 c*at 4K was unaltered by fields up to 60 kOe applied along [100]. At 60 kOe a ferromagnetic (FM) component appeared in the (002) intensity, while the total moment in the plane perpendicular to [110] remained essentially equal to the zero field value of 7.5 &mgr;B. Zero field satellite intensities (002±0 were reduced by a factor of 5 while the (110±) satellites were lower by more than a factor of 20 at 60 kOe. The results suggest the development of a fan structure with a fundamental (FM) component&mgr;o = 3.8 &mgr;Balong [100] and an angular width decreasing with field to 45° at 60 kOe. Such a structure contributes intensity to first order satellites of (002) but not of (110) as observed.

ISSN:0094-243X    

DOI:10.1063/1.2953887

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Magnetic form factor calculations have been performed using 4f wave functions obtained from relativistic Hartree‐Fock‐Slater calculations for free, and Wigner‐Seitz, gadolinium atoms and ions. Only small differences exist between our results for free Gdoand free Gd3+, and between free‐atom and Wigner‐Seitz results for Gdo; however, significant changes are observed as the amount of exchange is varied in the Hartree‐Fock‐Slater calculation. A comparison of our results with previous calculations and recent experiments led us to conclude that conduction electron screening produces only minor effects on the form factor, with the major difference between experiment and previous calculation probably being due to indirect relativistic screening.

ISSN:0094-243X    

DOI:10.1063/1.2953888

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The energy spectrum of magnons propagating along the [001] and [110] directions in ferromagnetic dysprosium at 4.7° and 78°K has been determined by triple‐axis neutron spectrometry. Throughout this temperature range the measured energy gap at zero wave vector (q⇒ ⇒ 0) is approximately 40% larger than that calculated from the macroscopic magnetostriction and crystal‐field anisotropy constants. Although the magnon energies increase with decreasing temperature, the variation nearq⇒ = 0is much stronger than that near the Brillouin zone boundaries. Thus, the magnitude of the exchange interaction decreases substantially, ∼25% in the c‐direction, between 78° and 4.7°K. Significant magnon‐phonon interactions are observed, particularly in the [110] direction where the acoustic magnon branch appears to be mixed with both the longitudinal and transverse acoustic phonon branches.

ISSN:0094-243X    

DOI:10.1063/1.2953889

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Dilute alloys of the heavy rare earths in yttrium are known to possess antiferromagnetic long‐range order. Below the Ne´el temperatures, Tb, Dy, and Ho alloys exhibit helical structures and the angles between the moments in adjacent planes along the c‐axes saturate at a value of about 50° in the low concentration limit. These facts suggest that the magnetic order in these dilute alloys is determined mainly by the RKKY exchange interaction &khgr;(q), which is proportional to the generalized susceptibility &khgr;(q) for the conduction electrons of yttrium. In order to obtain information about the J(q), the spin‐wave dispersion curve in the c‐direction of Y(10%Tb) has been measured at 4.7°K by means of the coherent inelastic scattering of neutrons. In spite of the low concentration of magnetic atoms well defined neutron groups were observed. The data have been analyzed on the basis of the frozen‐lattice model in which the equations of motion are averaged over randomly distributed sites of the magnetic atoms. The resulting J(q), which may be interpreted to be characteristic of Y, shows a much larger peak at the wave vector of the helical structure than those obtained for pure rare earth metals. The anisotropy constant obtained in the analysis was smaller than that for pure Tb.

ISSN:0094-243X    

DOI:10.1063/1.2953890

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Neutron inelastic scattering has been used to observe crystal field splittings in the rare‐earth compoundsTmNandTmBi. The measurements were obtained with time‐of‐flight methods utilizing a magnetically pulsed neutron beam and the cross‐correlation technique. Neutron scattering data were obtained simultaneously at three diffrent scattering angles and the relative neutron intensities for the three different momentum transfers show that the observed peaks arise from crystal‐field rather than phonon processes. A simple effective point charge model is sufficient to provide an interpretation of both the spacing and the intensities of the observed lines. Measurements were also made for the compoundsHoNandHoSbut the absence of distinct intense lines suggests that the exchange field may dominate the crystal field in these compounds.

ISSN:0094-243X    

DOI:10.1063/1.2953891

出版商:AIP    

年代:1972

数据来源: AIP