Showing papers by "W. C. Koehler published in 1962"

Magnetic Structures of Thulium

Abstract: Neutron diffraction studies on polycrystalline and singlecrystal specimens of thulium were made at room temperature to 1.3 deg K. The results are interpreted by a method exhibiting explicitly the Fourier components of the distribution of magnetic moments on the lattice sites. At about 56 deg K, the Neel temperature, a simple oscillating zcomponent-type antiferromagnetic structure is developed. At approximately 40 deg K, nonzero Fourier coefficients of overtones of the fundamental observed at higher teraperatures are first detected. At 4.2 deg K, the magnetic structure of thulium is a type of antiphase domain structure in which several layers of moments parallel to the + a/sub 3/ direction are followed by several layers in which the moments are oppositely directed. The sequence in thulium is --4, +3, --4, +3,... etc. Each atom has, within the precision of the experiments, an ordered moment of 7 mu s, and the ferrimagnetic structure has a net moment, parallel to the c axis, of 1 mu /sub B/ per atom. The fundamental period of the modulation remains constant over the whole range of teraperatures at a value corresponding to 3.5 a/sub 3/ periods. The scattering amplitude of thulium is b/sub Tm/ = (0.69 plus or minusmore » 0.02) x 10/sup -12/ cm. (auth)« less

Antiferromagnetism of the Antiphase Domain Structure of Pd 3 Mn

Abstract: Neutron diffraction measurements were made on polycrystalline samples of a 75% Pd---25% Mn alloy. It was found that long-range positional order could be obtained by appropriate heat treatment and that this order was of the one-dimensional antiphase domain type with a period of 4 cubic unit cells. Below 170\ifmmode^\circ\else\textdegree\fi{}K antiferromagnetic reflections were observed for this ordered alloy. A magnetic structure is proposed which satisfactorily accounts for the observed magnetic reflection intensities. On the basis of this structure the atomic magnetic moments are $(4.0\ifmmode\pm\else\textpm\fi{}0.2){\ensuremath{\mu}}_{B}/\mathrm{Mn}$ and $(0.2\ifmmode\pm\else\textpm\fi{}0.1){\ensuremath{\mu}}_{B}/\mathrm{Pd}$.

Investigations of Paramagnetic Neutron Scattering from Chromium

Abstract: Neutron diffraction investigations on ${\mathrm{Cr}}^{52}$ indicate that localized atomic magnetic moments do not exist in metallic chromium above the N\'eel temperature. Therefore, the moments which exist in the antiferromagnetic structure are presumably induced during the ordering process.

Neutron Diffraction Investigations of Ferromagnetic Palladium and Iron Group Alloys

Abstract: In order to account for the magnetic properties of alloys it becomes important to determine the individual magnetic moments of the constituent atoms. This determination can be accomplished by the combination of neutron diffraction and magnetic induction measurements. Such measurements were made on the following ferromagnetic alloys: Pd3Fe, PdFe, Pd3Co, PdCo, Ni3Co, and NiCo. The average moment values were obtained from magnetic induction measurements while the differences in the atomic moments were determined from either the ferromagnetic diffuse scattering of the disordered alloys or the superlattice reflections of the ordered alloys.

Neutron Diffraction Study of Magnetic Ordering in Thulium

Abstract: Neutron diffraction measurements have been made on a single-crystal specimen of metallic thulium at temperatures ranging from 293° to 4.2°K. In the temperature range between 38° and 56°K the magnetic structure of thulium is similar to that observed for the high temperature form of erbium; namely, a simple oscillating z-component type antiferromagnetic structure. Below 38°K additional satellite reflections are observed in the diffraction patterns from which it is inferred that the sinusoidal modulation is modified below this temperature. At 4.2°K the normal lattice reflections show an increase in intensity in zero field which is consistent with a mean magnetic moment per thulium atom of approximately one Bohr magneton directed parallel to the c axis. The low temperature magnetic structure which is proposed for thulium is one in which the moments are parallel to the c axis of the crystal but change their orientations according to the sequence 4, 3, 4, 3.... The fundamental period of the modulation remains constant over the entire range of temperature at a value corresponding to 3.5 a 3 periods.

Recent magnetic neutron scattering investigations at oak ridge national laboratory

Abstract: A brief summary is given of recent neutron diffraction investigations at the Oak Ridge National Laboratory on rare-earth metals and nntermetallic compounds. (auth)