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15 Mar 1971

Volume 42, Issue 4, pp. 1243-1818

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back to top TRANSITION‐METAL ALLOYS I

57Fe Hyperfine Fields in Iron‐Cobalt Alloys

G. K. Wertheim, D. N. E. Buchanan, and J. H. Wernick

J. Appl. Phys. 42, 1602 (1971); http://dx.doi.org/10.1063/1.1660356 (2 pages) | Cited 9 times

Online Publication Date: 19 December 2003

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The perturbation of the 57Fe hfs field by cobalt atoms in the first four coordination spheres of bcc iron has been obtained by using satellite line positions known from NMR data as constraints in the analysis of Mössbauer spectra. We assume that the perturbation decreases with increasing iron‐cobalt distance and that the effects of multiple neighbors are additive. Solutions violating the first assumption were also investigated but were found to be no better than those reported here. The results clearly show that the NMR satellite at Δν∕ν = +1.3% is due to a third‐neighbor cobalt in agreement with the proposal of Mendis and Anderson. The perturbation due to a near neighbor cobalt is insensitive to outer shell assignments and is (+3.5±0.3) %. That due to a second neighbor is (+3.0±0.6) % but is less well determined. The large probable errors in these two coefficients arise from strong correlation between them in the least‐squares analysis. The coefficient for the fourth‐neighbor shell was assigned the NMR value. The data also show small isomer shifts due to cobalt neighbors.

Electronic and Magnetic Structure of Dilute Iron‐Base Alloys

W. E. Sauer and R. J. Reynik

J. Appl. Phys. 42, 1604 (1971); http://dx.doi.org/10.1063/1.1660357 (2 pages) | Cited 6 times

Online Publication Date: 19 December 2003

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Mössbauer spectroscopy has been used to characterize changes in the electronic and magnetic structure of iron resulting from dilute additions of vanadium, chromium, manganese, nickel, molybdenum, tungsten, rhenium, aluminum, and silicon. The data showed that both the isomer shift and the hyperfine field depend linearly upon the bulk composition of the alloy and the local atomic configuration. This model separates the metallurgical dependence of these electronic and magnetic parameters into a long‐range composition‐dependent component and a short‐range composition‐independent component. The long‐range component of isomer shift in iron‐chromium alloys agrees with the value predicted by x‐ray diffraction measurements of the lattice parameter dilation. The short‐range component correlates qualitatively with the electronegativity of the diluents.

Mössbauer Study and Molecular Field Theory of the Magnetic Properties of Fe☒Al Alloys

G. P. Huffman

J. Appl. Phys. 42, 1606 (1971); http://dx.doi.org/10.1063/1.1660358 (2 pages) | Cited 23 times

Online Publication Date: 19 December 2003

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Mössbauer studies of the antiferromagnetic alloys, Fe1−xAlx (x≈0.33 to 0.47), have been made from 1.8° to 295°K. Supplementary low‐temperature susceptibility measurements were also carried out. The alloys have the CsCl structure and are best described as two interpenetrating simple cubic lattices, one of pure Fe, the other having composition Al1−cFec (c=1−2x). Fe atoms on the Al1−cFec sublattice (FeA) have nearly the full moment of pure Fe, while most atoms on the Fe sublattice (FeF) have zero moment. The hyperfine fields at both sites have a T2 temperature dependence for (T/TN)2≲0.6. At T = 0, the FeA field consists of a −145‐kG core polarization field plus an RKKY conduction electron polarization (cep) field, while the FeF field is given primarily by an RKKY cep field. The RKKY cep fields and Néel temperatures increase linearly with c. A molecular field theory is outlined which considers RKKY exchange interactions between Fe spins out to fifth nearest‐neighbor distances and a direct d electron exchange interaction between nearest‐neighbor spins. The theory explains the observed properties of the antiferromagnetic state and predicts with reasonable accuracy the magnetic phase diagram of the whole Fe☒Al system.

Measurements of Pressure Dependence of Magnetic Moment in Iron‐Aluminum Alloys

J. E. Noakes, H. Sato, and Anthony Arrott

J. Appl. Phys. 42, 1608 (1971); http://dx.doi.org/10.1063/1.1660359 (2 pages) | Cited 1 time

Online Publication Date: 19 December 2003

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A method of measuring the change in magnetic moment with pressure for spherical samples at a relatively low pressure level is described. Special attention is paid to the problem of avoiding the effects of sample motion with respect to the detector coil to insure the accuracy in such a highly sensitive measurement. The results of measurements on iron‐aluminum alloys up to 30 at.% Al are presented here. There is a sharp increase in the pressure dependence of the magnetic moment with the aluminum concentration. This is interpreted as favoring a competing antiferromagnetic interaction with increasing pressure.

Analysis of Diffuse Elastic Neutron Scattering from Magnetic Alloys

J. W. Garland and K. H. Bennemann

J. Appl. Phys. 42, 1610 (1971); http://dx.doi.org/10.1063/1.1660360 (1 page)

Online Publication Date: 19 December 2003

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In many magnetic alloys the local moment μn on site n depends nonlinearly on its local environment. A simple one‐dimensional model is used to illustrate the profound effect on diffuse elastic neutron scattering of this nonlinear dependence on local environment. It is shown how to extend the analysis of Marshall1 to include such a nonlinear dependence. It is shown why the cloud model of Kouvel et al.2 is preferable to the analysis of Marshall for a dilute concentration of clouds in Cu:Ni alloys, and the cloud model is derived from our general formulas. The case in which μn depends on the moments μn′ is also considered.

Effect of Pressure on the Magnetic Transition of MnAsxSb1−x Solid Solutions

L. R. Edwards

J. Appl. Phys. 42, 1610 (1971); http://dx.doi.org/10.1063/1.1660361 (1 page)

Online Publication Date: 19 December 2003

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The ferromagnetic transition temperatures of MnAsxSb1−x solid solutions for 0≤x≤1 have been measured as a function of pressure up to 4.5 kbar. Goodenough et al.1 have shown that for the alloys in the composition range 0.9≲x ≤ 1 the magnetic transition is first order and is accompanied by a hexagonal to orthorhombic structural transformation, while for 0 ≤ x≲0.9 the magnetic transition is second order. We find that this system exhibits a number of unusual features: (i) The change from first to second‐order behavior occurs within a narrow concentration range 0.88<x<0.9; (ii) the initial pressure derivative of the transition temperature dTc∕dP changes discontinuously in the concentration range 0.88<x<0.9; (iii) the transition temperature Tc exhibits a rather sharp minimum near this range. In the second‐order regime dTc∕dP decreases from −3 to −6.3°C∕kbar as x increases. On the basis of an itinerant ferromagnet model it has been demonstrated that dTc∕dP is related to Tc by the following equation2
math
.We find for the alloys in the concentration range 0≤x≤0.75 this relation is obeyed. We have also studied in some detail the T—P magnetic phase diagram of MnAs0.9Sb0.1 and find it to be qualitatively similar to pure MnAs. The main difference is that the critical pressure to stabilize the orthorhombic phase is increased by approximately 1 kbar.

Clustering and Giant Moments in Cu☒Ni Alloys

J. Jach, R. J. Borg, and D. Y. F. Lai

J. Appl. Phys. 42, 1611 (1971); http://dx.doi.org/10.1063/1.1660362 (2 pages) | Cited 5 times

Online Publication Date: 19 December 2003

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There are several studies of paramagnetic susceptibility and neutron diffraction revealing the presence of giant moments associated with chemical clustering. However, in contrast to the paramagnetic state, there are but few analogous studies extending below Tc. We prepared Cu☒Ni alloys of about 50–50 composition as Mössbauer sources containing 57Co. Internal fields, Tc, and isomer shifts were determined as functions of composition and heat treatment. The temperature dependence of the hyperfine spectrum changes very little as a result of annealing at low temperature. Nevertheless, the value of Tc itself dramatically increases in response to clustering, and the isomer shift and internal field at ∼0°K are singificantly altered in response to the change in chemical short‐range order.

Localized Polarization on Sn Atoms in Ferromagnetic Transition Metals and Alloys

G. P. Huffman and G. R. Dunmyre

J. Appl. Phys. 42, 1613 (1971); http://dx.doi.org/10.1063/1.1660363 (2 pages) | Cited 7 times

Online Publication Date: 19 December 2003

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We have made 119Sn Mössbauer measurements on an alloy of Fe0.5Ni0.5 containing 1 a∕o 119Sn from 4.2 K to the Curie point. 57Fe Mössbauer measurements were also made from 4.2 to 300 K. The hyperfine field at 119Sn nuclei behaves anomalously, decreasing much faster with temperature than does the magnetization, in a manner similar to that observed in Co. We interpret this anomalous behavior as being caused by a localized polarization associated with the Sn impurity and are able to fit the field‐vs‐temperature data well with a localized moment molecular field theory. A model of the Anderson type is outlined which indicates how localized polarization can form on a ``nonmagnetic'' impurity.
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