R. J. Begum

Magnetic Structure of MnAlGe

The ternary alloy MnAlGe has been studied by diffraction techniques using both neutrons and x rays. The unit cell is found to be tetragonal with a0 = 3.914±0.001 A and c0 = 5.933±0.001 A. The space group is D4h7‐P4/nmm. The intensities in the neutron‐diffraction patterns agree with a ferromagnetic spin alignment of the Mn atoms with a magnetic moment of 1.40±0.12 μB each. The magnetic field dependence of the diffracted neutron intensities reveal a high magnetic anisotropy and a high retentivity.

Magnetic structures in the iron-germanium system

Abstract Three phases in the iron-germanium system have been investigated by neutron diffraction for determining their atomic and magnetic structures. Of these, FeGe 2 is found to be antiferromagnetic with a Neel temperature of 315°K and Fe 1.67 Ge is ferromagnetic having a Curie temperature of 510°K. There is evidence of a distortion of the ideal “filled” NiAS structure in the case of the latter. FeGe is paramagnetic down to 140°K.

Polarised neutron diffraction study of nickel ferrite

Abstract Polarised neutrons have been used to solve the existing ambiguities in the chemical and magnetic structures of NiFe 2 O 4 . The results show conclusively that it has a completely inverted spinel structure with an oxygen parameter of 0.2573 ±0.0003. The observed magnetic moments at room temperature show that nickel ferrite exhibits the Neel ferrimagnetism with m ( A )Fe = 4.86μ B , m ( B )Fe = 4.73μ B and m ( B )Ni = 2.22μ B leading to a net moment of 2.09μ B . The Debye-Waller temperature correction was determined with the constant B = 0.8 × 10 -16 cm 2 .

Ferrimagnetic structure of Mn2Co2C

Abstract The carbide Mn 2 Co 2 C has been found to be ferrimagnetic with a Neel temperature of 535°C by means of neutron diffraction. It has a cubic unit cell with an Mn atom at the cube corner and the Carbon atom at the body centre. The face centre sites are taken up by the other Mn and the two Co atoms in a statistical manner. The Mn moments are aligned anti-parallel to each other while the two Co moments are parallel to the comer Mn moment. The most reasonable values for the moments are: 4.0 μ B for the corner Mn atom, 3.36 μ B for the face centre Mn and 1.25 μ B for each Co atom. The smaller moments of the face centre atoms arise from the influence of the carbon atom. Polarised neutrons were used to choose a structure having cubic symmetry over one of tetragonal symmetry.

Investigation of Ferrimagnetism in Some Compounds using Polarized Neutrons

Polarized neutrons offer a very useful method of studying ferrimagnetic materials such as ferrites, in which the multiplicity of cations and their valence states prevent a unique determination of the spin structure when only polycrystalline material is available. This paper presents the first extensive use of polarized neutron powder‐diffraction patterns for determining the structure of a carbide of Mn and Co and of a number of mixed ferrites having the spinel structure.The ferrimagnetic carbide with composition (Mn,Co)4C is found to have a cubic structure of the Mn4N type, with one of the Mn atoms at the cube corner and the face centers being occupied by one Mn and two Co atoms in a statistical distribution. The two Mn atoms are antiferromagnetically aligned with respect to each other, the corner atom having a moment of 4.0 μB while the face center moment is 3.0 μB. The two Co atoms have a moment of 0.8 μB each and are aligned parallel to the corner Mn moment along the cube edges. The material has a Neel...