L. M. Corliss

Magnetic Structure of Cr2O3

Pratt and Bailey have recently explained the optical and anomalous magnetic properties of Cr2O3 by means of a model consisting of the basic Cr2O3 antiferromagnetic structure with moments canted away from the c axis and forming some kind of spiral. Our neutron powder‐diffraction data confirm the original Brockhouse moment configuration but indicate that the c‐axis component of the Cr moment is 8% lower than the spin‐only value. This result can be interpreted as supporting the canted model of Pratt and Bailey. A careful search has been made, using single crystals, to find evidence for an ordered or spiraling perpendicular component. Polarization studies establish that there is no magnetic contribution to the fundamental reflections other than that arising from the c‐axis components. A survey of reciprocal space revealed extra spots at forbidden positions, but these could be accounted for semiquantitatively in terms of double‐Bragg scattering. We conclude, therefore, that either the Cr moment is intrinsicall...

Investigation of the Magnetic Structure of ErMn2, TmMn2, TbNi2 by Neutron Diffraction

Magnetic measurements by H. J. Williams (ErMn2 and TmMn2), and W. E. Wallace (TbNi2) have shown that these compounds are magnetically ordered at low temperature with a net moment per formula unit lower than that of the free rare‐earth ion. Neutron diffraction powder patterns have been used to determine the actual magnetic structure. ErMn2 and TmMn2 crystallize with the hexagonal Laves phase structure (C‐14 type). ErMn2 is ferromagnetic, with a moment of 7.72 μB/Er atom at 4.2°K aligned along the c axis. No detectable moment on Mn is observed. TmMn2 is almost completely ferromagnetic, with a moment of 4.95 μB/TM atom at 2.1°K aligned along the c axis, and essentially zero moment for Mn. A faint additional line at low angle seems to indicate a weak antiferromagnetic contribution. TbNi2 crystallizes with the cubic Laves phase structure (C‐15 type). At 4.2°K, ferromagnetic lines as well as additional peaks appear in the diffraction pattern, but the magnetic scattering is rather sensitive to sample preparation.

Neutron Diffraction Study of the Pseudobinary System ErCo2–ErAl2

Results obtained by neutron diffraction indicate that the magnetic moment of the ferromagnetic sublattice in the Laves phase structures, C15 (ErCo2, ErAl2) and C14 (ErCoAl), varies with composition while the ordering temperatures stay approximately constant. Low values of the aligned moment, however, are accompanied by high values of the disorder scattering at low temperatures. Co carries no moment from 30 mole % ErAl2 on. Results are discussed in terms of tendencies toward antiferromagnetism at certain values for the valence electron concentration.

An order-disorder transition in Sr2IrD5: Evidence for square pyramidal IrD5 units from powder neutron diffraction data

Abstract Neutron diffraction data have been collected on a powdered sample of Sr2IrD5 over a range of temperatures. The compound, which is cubic at room temperature, has been found to exhibit a gradual transformation to a tetragonal phase in the temperature range 200-140 K. As a result of the transition, deuterium atoms which randomly occupy sixfold positions in the cubic phase, become tetragonally ordered. A small fraction of the cubic phase remained untransformed at 4.2 K. Both the cubic and tetragonal structures are consistent with square pyramidal IrD5 units with average IrD distances of 1.714 and 1.718 A, respectively. Agreement factors, R1, for the two structural analyses are 3.44 and 4.94%.

The structure of ce-doped Bi2(MoO4)3 as determined by neutron profile refinement

Abstract The structure of Bi 1.8 Ce 0.2 (MoO 4 ) 3 has been refined with powder neutron diffraction data by the Rietveld method. The structure can be derived by severely distorting the scheelite structure ( AM O 4 ) and is perhaps better written A 2 3 O 1 3 M O 4 , where O = cation vacancy. Of the two bismuth atom sites, cerium preferentially occupies the more symmetric of the two (Bi(2) in the structure) with some cerium found in the scheelite subcell vacancies also. This site preference is understood by examining the symmetries of the two Bi sites. Crystal data: monoclinic, space group P2 1 c , Z = 4, a = 7.697(2), b = 11.535(3), c = 11.944(3) , β = 115.19.

Magnetic Structure and Metamagnetism of HgCr2S4

HgCr2S4 is a normal cubic spinel whose metamagnetic properties were first reported by Baltzer et al. Our neutron diffraction studies show that the magnetic structure at 4.2°K is a simple spiral, identical with that proposed by Plumier for ZnCr2Se4. The propagation vector τ is parallel to the symmetry axis of the spiral and directed along a particular cube edge in a given domain. The moment of Cr3+ is 2.73 μB, in agreement with the magnetization measurements, and the wavelength of the modulation is ∼42 A. The wavelength increases with temperature, reaching a value of ∼90 A at 30°K, and shows very little further variation up to the Neel point (∼60°K). Application of a magnetic field along a cube edge produces no magnetization in that direction, but rather a growth of domains for which τ ‖ H. This process is complete at ∼4 kOe and is followed by a rapid collapse of the spiral into the field direction which saturates at ∼10 kOe. The growth of favorably oriented domains decreases progressively as the direction...

Magnetic Structure of MnSn2

An abrupt magnetic transition in MnSn2 was reported by Kouvel and Hartelius1 about one year ago. The salient features of the magnetic behavior are a smooth susceptibility maximum at 86°K and an almost discontinuous decrease in susceptibility at 73°K. At the suggestion of Kouvel, a neutron diffraction study was made to investigate possible changes in magnetic structure accompanying the transition.MnSn2 has the body‐centered tetragonal C16 structure, consisting of alternating layers of Mn and Sn perpendicular to the c axis. Each Mn atom is surrounded by 8 Sn atoms which connect it to its second and third nearest neighbors through angles of approximately 111° and 146°, respectively. Nearest‐neighbor Mn atoms have no intervening Sn atoms and are separated by a distance of 2.72 A in the c direction.Neutron diffraction patterns show that above the abrupt transition at 73°K, MnSn2 is antiferromagnetic with a Neel temperature in the neighborhood of 330°K, in agreement with recent susceptibility and resistivity me...

Neutron Diffraction Studies of Cold‐Worked Brass

Powder diffraction data with neutrons have shown the integrated intensities to be identical in cold‐worked (filed) and annealed brass with no trace of extinction effects. Long wavelength transmission studies have also shown that the diffuse scattering is increased by less than 0.4 percent upon severely cold rolling brass. A new technique of examining the Bragg discontinuities supports the hypothesis that the major part of the broadening is due to lattice distortion. Some remarks are presented concerning the analogy between long wavelength neutrons and conduction electrons with respect to scattering by dislocations. The effects of dislocations on coherent scattering are also considered.

Paramagnetic Susceptibilities of Solid Solutions of MnF2 and ZnF2

The paramagnetic susceptibilities of solid solutions of MnF2 and ZnF2 have been measured as a function of temperature. The Curie‐Weiss law X=C/T+Δ is obeyed by all the solutions examined over the temperature range 76°—295°K. The constant Δ was found to be a linear function of the mole fraction of MnF2. This behavior is consistent with the assumption that the magnetic interaction energy associated with a given ion is proportional to the number of its paramagnetic neighbors.

Structure and magnetism of Eu2IrD5

Abstract A powder neutron diffraction study of Eu1532IrD5 has shown it to be isostructural with Sr2IrD5 at room temperature. Unlike the latter compound, it does not undergo a deuterium-ordering transition at low temperatures. Magnetic scattering at helium temperatures confirms the suggestion that it becomes ferromagnetic below 20 K with a moment corresponding to that of divalent europium.