Moment Of Transition Metal Research Articles

Magnetic anisotropy of Ho2Co17 and Ho2Fe17

The magnetic anisotropy energy K1, the energy to rotate the magnetization from the easy basal plane to the unique axis, has been measured in Ho2Co17 and Ho2Fe17, both by the magnetization curve and by neutron diffraction. Neutron diffraction studies have been taken to imply a K1 for Ho2Co17 a factor eleven times larger than that measured by magnetization measurements. For Ho2Fe17 the discrepancy may be as large, if one also takes K2 into account. We show that the two sets of measurements are compatible; what has obscured the interpretation of the measurements is the canting of the rare earth and transition metal moments, induced by the field and by the anisotropy torques.

Analysis of magnetic interactions and structure in R6Mn23

The magnetic properties of R6Mn23 compounds are examined, with emphasis on representatives of the light rare earths. An exceptional antiferromagnetic coupling of light rare earth and transition metal moments is found to exist. A non-collinear model for the rare earth sublattice suggested elsewhere is generally satisfactory, but calculations of the exchange parameters suggest partial moment reorientation from the proposed configurations. Properties associated with important coercive materials such as large rare-earth transition metal exchange and uniaxial anisotropy are absent in the R6Mn23.

Site preference and local environment effects in ferromagnetic ternary alloys

Using 57Fe Mössbauer Effect and 59Co NMR in the system Fe3−xCoxAl, we show that Co substitutes preferentially the Fe at the (A, C) sites in the Heusler (L21) structure. The transition metal moment and the hyperfine field is seen to be very intensitive to the local environment.

On the magnetic properties of Y(Fe xCo 1- x) 2 compounds

The composition dependence of the mean magnetic moment of cobalt atoms in Y(Fe x Co 1- x ) 2 compounds is analysed in the local environment model. Cobalt has a magnetic moment of 1.56 μ B if there are at least two Fe atoms as nearest neighbours. The maximum in the composition dependence of the transition metal moments is due to the magnetic contributions of iron atoms only. The thermal variation of reciprocal susceptibility obeys a Curie-Weiss behaviour, in addition to the Pauli paramagnetic term. Finally, the influence of the variable magnetic interactions on the transition metal moments is discussed.

On the magnetic properties of Y(Fe xCo 1−x) 2 compounds

The composition dependence of the mean magnetic moment of cobalt atoms in Y(Fe xCo 1−x) 2 compounds is analysed in the local environment model. Cobalt has a magnetic moment of 1.56 μβ if there are least two Fe atoms as nearest neighbours. The maximum in the composition dependence of the transition metal moments is due to the magnetic contributions of iron atoms only. The thermal variation of reciprocal susceptibility obeys a Curie-Weiss behaviour, in addition to the Pauli paramagnetic term. Finally, the influence of the variable magnetic interactions on the transition metal moments is discussed.

Studies on compounds DyFe 3, Dy 6Fe 23 and Dy 2Fe 17 with al substitution for Fe II: magnetic investigations

Magnetization and susceptibility measurements on pseudobinary alloys Dy 0.25 Fe 0.75− x Al x , Dy 0.207 Fe 0.793− x Al x and Dy 0.105 Fe 0.895− x Al x are reported for temperatures from 4.2 K to about room temperature. The magnetization behavior in the ordered regime indicates that the coupling scheme between the rare earth and the transition metal moments stays antiferromagnetic on Al substitution for the transition metal. All substituted materials develop respectable intrinsic magnetic hardness at cryogenic temperature. The origins of this effect are slightly different in Dy 2(Fe, Al) 17 than in all other Al-substituted materials. In the former case, the relatively high values of H c ( H c = 40 kOe at 10 K) appear to be due primarily to a state close to compensation of Dy and Fe sublattice magnetizations. The other cases of intrinsic magnetic hardness are primarily connected with partial magnetic disorder (magnetic scatter order) which in turn results in extraordinarily thin domain walls. These domain walls become pinned at obstacles of atomic dimensions.

Hydrogen absorption in CeFe 2 and ThFe 3

The effect of hydrogen absorption on the magnetic properties of CeFe 2 and ThFe 3 was studied by magnetization measurements and by the 57Fe Mössbauer effect. In both cases an increase in the transition metal moment is observed. In CeFe 2 the long range periodicity of the crystal lattice is lost whereas in ThFe 3 a structural change occurs. Surprisingly, the magnetic anomaly observed in ThFe 3 around 250 K is still present in the hydride.

Induced moments in gadolinium intermetallics

Magnetization measurements on the pseudobinary compounds in the GdCoNi series of intermetallics show that the transition metal moment (μ TM) is generally larger than that in the yttrium compounds. Anomalous behaviour is observed in the 2:17 compounds at a composition corresponding to the rhombohedral-hexagonal phase change.

MÖSSBAUER SPECTRA OF THE AMORPHOUS ALLOYS DyM3 (M = Fe, Co, Ni)

Amorphous alloys DyM3, M = Fe, Co, Ni, have been studied by the 161Dy and 57Fe Mossbauer resonances, doping with iron where necessary. 57Fe-doped YNi3 was also included in the study. Results are compared with those for the corresponding crystalline alloys. Iron hyperfine fields at saturation are considerably greater (~ 30 %) in the amorphous alloys, and there is a broad distribution whose relative width is ~ 20 %. Possible reasons for a greater transition metal moment in the amorphous alloys are discussed. The Dy hyperfine field at saturation is 1 % less than in the crystalline alloys, with a distribution whose relative width is only 1 %. From the widths of lines whose positions are sensitive to the quadrupole interaction, it is deduced that the Dy moment direction is strongly correlated with the (random) direction of the lattice contribution to the electric field gradient. Magnetic structures are proposed in which the Dy moments are essentially distributed over all directions within an hemisphere while the Fe or Co is ferromagnetic. The Ni moment is very small.

Atomic-volume deviations and occurrence of atomic magnetic moments in transition metals and their alloys

Abstract Deviations of the atomic volume from additivity are determined for binary compounds of non-magnetic transition metals (components with close group numbers), for compounds of the latter with Be and Mg, and for alloys of Gd, Mn, U and Np with transition and non-transition metals. In most compounds of non-magnetic transition metals (except those of U and Np) the deviation does not exceed 3%. The abnormally large negative deviation in γ-La, δ-Mn, γ-U, γ-Np, U 2Ru3, URe2, NpRe2, Os3Ta, BeMo3, etc., is probably related to occurrence of ferro- or antiferromagnetism in these phases.

Mössbauer and crystallographic study of DyFe3−x Nix compounds

Mössbauer and crystallographic investigations were carried out on DyFe3−x Nix compounds crystallizing in the PuNi3 type of structure. The hyperfine field observed at the iron sites shows a maximum at x =0.75. The 12-line spectrum observed at room temperature corresponding to the two different kinds of iron in the structure collapsed into a single six-line pattern at 4.2 K. Lattice parameter c shows a rapid decrease when x is increased beyond 2.0, but no such behavior was found in the a lattice parameter. The results of the x-ray and Mössbauer data are explained in terms of site preference and nonlocalized transition-metal moments, respectively.

Magnetic investigations on Tb0.25Fe0.75−xAlx and Tb0.105Fe0.895−xAlx

Magnetization and susceptibility measurements on pseudobinary alloys Tb0.25Fe0.75−xAlx and Tb0.105Fe0.895−xAlx are reported for temperatures from 1.6 K to about room temperature. The magnetization behavior in the ordered regime indicates that the coupling scheme between the rare-earth and the transition-metal moments stays an antiferromagnetic one on Al substitution for the latter. An unusual magnetization behavior is observed at the lowest temperatures (1.6–10 K). Here strong S-type saturation develops partly with spontaneous increases of magnetization at critical fields of the order of 20 kOe. This is a result of highly energetic domain walls connected with high anisotropy and disorder on crystallographic sites. Coercive forces up to about 14 kOe are observed in the pseudobinary region at 4.2 K.

Magnetic properties of DyFe 3−xCo x and HoFe 3−xCo x

Magnetic moments, Curie and compensation temperatures were measured for DyFe 3−xCo x and HoFe 3−xCo x compounds. The variation of transition metal moment has been explained on the basis of the rigid band model.

Localized magnetic moments in transition metals and alloys

The Anderson model generalized to the case of many impurities is studied within an approximation used by Roth in the single impurity case. The treatment attempts to take into account the correlation in the occupancy of the impurity orbital in the limit of infinite Coulomb repulsion. The effect of the interactions between impurities is studied in detail for the two impurity problem. Here one finds the occurrence of localized magnetic moments and their dependence on the character and strength of the interaction quite similar to that obtained in the Hartree-Fock theory with an appropriately chosen value for the Coulomb repulsion. For a given number of electrons in the impurity state, we find a parallel or antiparallel alignment of the moments energetically favorable depending on whether the interaction between the impurities is primarily direct or indirect. The formalism is extended to consider a dilute random alloy, and also transition metals and ordered alloys of transition metals with simple metals.

Transition metal moment collapse in Gd(Co 1- xNi x) 2

The magnitude of the transition metal moment in the series of compounds Gd(Co 1- x Ni x ) 2 has been derived from the observed molecular moments. Its variation with x shows a rapid decrease in the vicinity of x=0.5.

Exchange Coupling and Conduction-Electron Polarization in Metals. II

The effect on the isotropic spin density of the (k,k\ensuremath{'}) dependence of the exchange coupling $J(\mathbf{k},{\mathbf{k}}^{\ensuremath{'}})$ between a localized magnetic moment and conduction electrons predicted by Ruderman-Kittel-Kasuya-Yosida (RKKY) theory is determined quantitatively. Spherical local moments are employed, viz., $\mathrm{Gd}(4{f}^{7})$ and $\mathrm{Fe}(3{d}^{5})$ (which are taken as representative of rare-earth and transition metal moments, respectively). The conduction bands are described by simple orthogonalized plane waves appropriate to a free-electron metal with k the wave vector of the incident electron and k\ensuremath{'} that of the scattered electron. We find that a $Q$-dependent coupling (where $Q\ensuremath{\equiv}|\mathbf{k}\ensuremath{-}{\mathbf{k}}^{\ensuremath{'}}|$) has some justification when dealing with a Gd local moment but has considerably less justification for Fe. Both the (k,k\ensuremath{'}) and the $Q$-coupling schemes yield a main spindensity peak which is more diffuse than that yielded by coupling approximations traditionally applied to RKKY theory. Spin-density results were obtained which are appropriate to the outer reaches of a lattice site and to the nuclear site of either the local moment or neighboring atoms (these involve inclusion of core $s$ terms in the spin density). These results suggest that spin distributions obtained by neutron diffraction and those inferred from hyperfine field measurements may differ significantly.

Evidence for an itinerant electron moment in cubic Laves-phase rare-earth - transition-metal compounds

The magnetic properties of the series of pseudo-binary compounds YFeuCo2-u have been examined in an attempt to obtain further information concerning the nature of the transition-metal moment in the cubic Laves-phase rare-earth - transition-metal compounds. The variation of the observed moment throughout the series can be understood on the basis of a non-localized moment associated with the transition-metal ion. The variation of the Curie temperature may be associated with the variation of the lattice parameter between the terminal compounds.

Localized Moments in Transition Metals

Two types of nuclear magnetic resonance (NMR) studies are discussed which are pertinent to the magnitude and distribution of the magnetization associated with local moments in transition metals: (1) The unusual temperature dependence of the 55Mn NMR1 of 1.5% Mn in Fe, below Tc, is shown2 to result from the existence of a localized moment on the Mn and the fact that the Fe-Mn exchange interaction is smaller than the Fe-Fe exchange. (2) From studies of the 59Co NMR in dilute Co in Rh-Pd alloys evidence is obtained which suggests that the occurrence of localized moments in a binary alloy system is discontinuous— the apparent continuous behavior observed in magnetization measurements is a consequence of the statistical variation of near neighbors of a given kind to the impurity atom.3

Densities of states, superconductivity, and localized moments in transition metals

Correlations between density of states at the Fermi surface, superconductive transition temperature and the tendency of solute iron atoms to carry localized moments are examined for second and third transition group metals; the breakdown of expected correlations is ascribed to the change in character of the d-band wave functions.

Нейтронография магнитных материалов

A review of neutron diffraction of magnetic materials is presented. The topics covered include: (1) A discussion of slow neutron scattering including nuclear and magnetic effects, with examples and typical experimental arrangements. (2) The determination of magnetic moments. In this section various models for Fe4N and Mn4N is discussed, as are magnetic moments of FeNi3, Fe3Al, and magnetic moments of transition metals and magnetic moments in the paramagnetic region. (3) Magnetic structure of transition metals. In this section are presented results concerning the antiferromagnetic structure of these metals, principally chromium; a description of magnetic symmetry; and the new class of spiral structures. (4) Magnetic structure of some compounds: the perovskite group of iron compounds; the perovskite group of rare earth metals; the antiferromagnetism of transitron metal carbonates; and trifluorides of transition metals. The breakdown of Hund's rule rs discussed, as is the magnetic anisotropy of some manganese compounds. (5) Magnetic critical and small angle scattering of neutrons. A qualitative discussion of Van Hove's theory is given. Results of small-angle scattering from iron at various temperatures are presented. Distant and close magnetic interactions are briefly noted, as is the dynamics of spin correlations. (6) Scattering of neutrons by spin waves. Thismore » section includes a brief discussion of magnons; the dispersion law of spin waves; and experimental results of scattering by spin waves. (7) Magnetic scattering of conduction electrons; principally the electrical resistance of disordered magnetic structures. Spin interactions are mentioned in connection with superconductivity.« less