摘要:

Long‐range ferromagnetic coupling occurs in several dilute solid‐solution alloys of the ferromagnetic transition elements in Pd or Pt. New measurements of magnetic moments and Curie temperatures of PdFe, PtFe, PtCo, and PdNi alloys are reported, and previous work on these and some of the more general properties of these alloys are briefly reviewed. Also, ferromagnetism occurs in dilute PdGd solid solutions.Dilute solutions of iron in gold are ferromagnetic, although below about 10% of Fe there seems to be no homogeneous bulk ferromagnetism.

ISSN:0021-8979    

DOI:10.1063/1.1714264

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A number of the magnetic properties of rare‐earth ions, which depend strongly on their interaction with the crystalline environment, are inferred by studying their electronic spectra. Basic to current methods for analyzing these spectra is the assumption of a static crystalline fieldVcwhich acts on the open 4fshell. Generally, one takesVc=&Sgr;n,mAnmrnnYnm(&thgr;, &phgr;). In fitting observed spectra, matrix elements ofVcover the 4felectrons alone are considered and one is left with the quantitiesVnm=Anm⟨rn⟩ (where ⟨rn⟩ is the integral ofrnover the 4fradial density) which are taken to be empirical parameters which somehow absorb all environmental effects not included inVc. These empirical parameters have been used ``successfully'' to interpret other rare‐earth properties. However, if one considers multi‐electron Coulomb and exchange contributions arising from the closed shells, it may be shown1that, in addition to the occurrence of substantiallinear shieldingeffects1,2(which reduce the magnitude of theVnmparameters), there may be significant nonlinear shielding contributions which change the ordering and spacing of the electronic energy levels. When these latter terms are significant, the standard parameterization scheme breaks down.Previous work1on Ce3+, using perturbation theory techniques, was seen to be inadequate for accurate estimates of nonlinear shielding. We have extended these investigations using configuration interaction methods to estimate the leading nonlinear (and linear) shielding terms in a number of ions, Ce3+, Tb3+, Er3+, Tm3+, Ho3+, Dy3+, and Yb3+. Calculations have been carried out as a function of crystalline field strength since the nonlinear shielding is dependent, of course, on the strength of the applied external field. Nonlinear shielding ofV2andV4external fields were determined as a function of atomic number as were their effects on apparentV2,V4, andV6crystal field parameters. From these certain conclusions may be drawn. Antishielding rather than shielding of theV4field occurs, but only by a few percent at most, whereas theV2field is always shielded. For the heavy rare‐earth ions, the shielding effects are much smaller than for the lighter ions, with the apparentV4andV6shielding being very small. The most severe nonlinear effects arise when relatively strongV2andV4fields contribute to a relatively weakV6field.A full report will be submitted to the Physical Review.

ISSN:0021-8979    

DOI:10.1063/1.1714265

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

In the first part an approximate method to treat the problem of one impurity atom in an otherwise pure metal is developed on the basis of tight‐binding approximation. The method is capable of taking into account the degeneracy of the 3dbands and the mixing of the 3dbands with the 4sband. It is shown that one can treat each 3datomic orbital of the impurity atom separately.In the second part, dilute Ni alloys with other 3dtransition metals are discussed on a simple model. The calculation substantiates Friedel's theory of these alloys. The negative magnetic moments of Cr and V in Fe are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714266

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Several dihydrated formates including Ni(HCOO)2·2H2O and Fe(HCOO)2·2H2O crystallize in a monoclinic structure whose unit cell contains two each of two inequivalent types of metal ions. The temperature variation of the powder susceptibility, &khgr;p, of the Ni+ +salt suggests that those ions on one type of site become cooperatively ordered near 15.7°K while the rest remain essentially independent even at 1.3°K. &khgr;pfor the Fe+ +salt exhibits a huge peak at 3.68°K associated apparently with the long‐range ordering of moments on sites of both types. Mo¨ssbauer experiments at 300°K on the Fe+ +salt clearly distinguish ions on the two sites, the ratio of the effective electric field gradients being ∼5 to 1. The smaller field gradient is assumed to characterize the site (type 1) approximately octahedrally coordinated by oxygens from six formate groups. The Mo¨ssbauer spectrum near the transition point differs from those measured at 300°, 77°, 20°, and 4°K. The results show that the internal magnetic field is larger at the type 1 sites. Preliminary calculations using the observed nuclear hyperfine structure indicate that the ratio of magnetic fields at the two sites is about four to one.

ISSN:0021-8979    

DOI:10.1063/1.1714267

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The antiferromagnetic transition temperature of chromium‐rich V‐Cr alloys has been investigated by means of the extinction of the51V and53Cr NMR signals at the transition temperature in these alloys. Measurements on both natural and isotopically enriched53Cr chromium yieldTN=39.0±0.5°C, in excellent agreement with neutron diffraction results.TNdecreases roughly linearly with V content, falling below 4.2°K at 3.4% V. In all cases, the resonance intensity follows the empirical behavior,I=I0tanhK(1‐TN/T), whereK≈ 15. At temperatures well aboveTN, the linewidth and second moment of the53Cr resonance are appreciably larger than the calculated values based solely on nuclear dipolar broadening. These results might be attributed to the persistence of a very small electronic moment in the paramagnetic state.

ISSN:0021-8979    

DOI:10.1063/1.1714268

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Measurements of the119Sn isotropic and anisotropic Knight shifts,KisoandKax, have been made in a series of Sn3RE intermetallic compounds (RE=La, Ce, Pr, Nd, Sm, Eu, and Yb). In particular, PrSn3and NdSn3have large positive, temperature‐dependent shifts which are proportional to the magnetic susceptibility &khgr;M. It is proposed that the mechanism relatingKaxto &khgr;Min these cases is a coupling of the119Sn spin to the RE localized moment via the conduction electrons in a manner analogous to the pseudo‐dipolar interaction between nuclear spins in heavy metals. Similarly,Kisomay be regarded as arising from an isotropic indirect coupling betweenf‐electron spins and nuclear spins. Reasonable values of the interaction strengths are obtained.

ISSN:0021-8979    

DOI:10.1063/1.1714269

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The room‐temperature nuclear magnetic resonance absorption of59Co in an alloy of 0.5% Co in Ni has been measured under hydrostatic pressures of up to 7 kbars. The change in the resonance frequency with pressure is &Dgr;v/&Dgr;p=159±5 Hz/bar. This is in the same direction (increasing frequency for increasing pressure) as for61Ni in Ni. The ratio of the resonance frequency at absolute zero to the change in frequency with pressurev0: &Dgr;v/&Dgr;pis 750 kbar for59Co and 1200 kbar for61Ni in Ni. The internal field at the59Co nucleus decreases with increasing temperature more slowly than that at the61Ni nucleus in Ni‐rich Ni‐Co alloys. This discrepancy in the temperature dependences remains as large, when plotted at constant volume, as it was at constant pressure.

ISSN:0021-8979    

DOI:10.1063/1.1714270

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The coupling between films of NiFe and another ferromagnetic material separated by a thin layer of a nonferromagnetic metal has been investigated for the cases of Au, Ag, Cr, and Pd intermediates. It is found that for Pd an alloy formation takes place during evaporation, and that for Cr, a porosity effect is important. It appears unlikely that either of these effects can be important for Au and Ag, and in these cases the possibility of indirect exchange must be considered seriously.

ISSN:0021-8979    

DOI:10.1063/1.1714271

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Ne´el walls have been generally observed in Permalloy films below a certain thickness whereas thicker films seem to support Bloch walls or cross‐tie walls. Two coupled Permalloy films of 81% Ni‐19% Fe composition separated by a layer of silicon monoxide were used to study domain wall interactions. Ne´el walls with no Bloch lines were observed in 900‐Å coupled film segments with 300‐Å film separation. In a single layer of Permalloy of this thickness, Bloch walls predominate. Since the separating layer is an insulator and nonferromagnetic, the interaction is thought to be magnetostatic. The films were prepared in a step fashion on a single substrate so that uncoupled and coupled portions of a film, prepared in the same evaporation, could be observed simultaneously using Bitter powder pattern technique. Multiple‐step coupled structures of varying film thickness with constant separation and varying separation with constant film thickness were prepared with thicknesses chosen in the region of Ne´el‐Bloch transition. The coercive force of the coupled film segments is lower than that of similar uncoupled film segments. The coercive force starts to decrease at film separations of approximately 1100 Å.

ISSN:0021-8979    

DOI:10.1063/1.1714272

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Films of Co&sngbnd;Ni, varying in composition from 30% Co to 100% Co, and ranging in thickness from 250 to 2500 Å, were prepared by chemical deposition. Small amounts of P were also included in the deposit. Their crystallographic and magnetic properties were studied as a function of composition and thickness. X‐ray diffraction revealed a hexagonal structure for the Co films, with increasing presence of a cubic phase as Ni was introduced. The hexagonal crystallites of the all‐Co films were randomly oriented, but in the Co&sngbnd;Ni films there was an increasing orientation of the hexagonal (002) and cubic (111) axes perpendicular to the substrate. The coercivity for a particular thickness increased as the Ni content of the films increased, reaching a peak of about 1300 Oe at 10% to 30% Ni depending on the thickness. Beyond this, the coercivity decreased rapidly to a value of 200 Oe as the Ni content of the films increased to 70%. In the Co films the coercivity decreases markedly with increasing thickness. This dependence on thickness becomes less and less pronounced as Ni is introduced, until the coercivity becomes independent of thickness in the vicinity of 20% Ni. Thereafter, the coercivity increases with increasing thickness, and this effect becomes more evident at higher Ni contents.

ISSN:0021-8979    

DOI:10.1063/1.1714273

出版商:AIP    

年代:1965

数据来源: AIP