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For Li 0.92 Mn 2 O 4, on the other hand, the absence of a long-range spin-ordered state is confirmed down to 1.5 K. The commensurate magnetic structure ( k C = 0.5, 0.5, 0.5) follows the magnetic anisotropy of the local easy axes of Mn 3 +, while the incommensurate Mn 4 + one shows a spin-density-wave or a cycloidal order with k IC = ( 0, 0, 0.216 ). Surprisingly, the two antiferromagnetic orders are found to be independent of each other. This technique can be applied to study crystalline solids, gasses, liquids or amorphous materials. Below T N, two antiferromagnetic transitions are observed: (i) a commensurate long-range Mn 3 + spin ordering below T N 1 = 35 K and (ii) an incommensurate Mn 4 + spin ordering below T N 2 = 11 K. Neutron diffraction experiments determine the atomic and/or magnetic structure of a material. Above T N = 35 K, a two-dimensional short-range correlation is observed, as indicated by asymmetric diffuse scattering. Neutron powder diffraction provides insight into the crystal and magnetic structures of materials. The SRM is certified with respect to the lattice parameter of the Si substrate. It consists of 25 mm x 25 mm pieces of a silicon wafer with a Si-Ge epilayer. It is evident that one of the Mn sites shows a strongly distorted Mn 3 + octahedron due to the Jahn-Teller effect. The new SRM 2000 is the first thin-film, high-resolution diffraction SRM. The present crystal structural analyses of NaMn 2 O 4 reveal that a Mn 3 + / Mn 4 + charge-ordering state exists even at low temperature (down to 1.5 K). In these notes we give a short review, at an introductory level, of some topics concerning the study of crystal structures by means of neutron powder diffraction. Neutron powder diffraction is a powerful technique to clarify the relationship between the crystal structures and the properties of functional materials. Ideally, every possible crystalline orientation is represented equally in a powdered sample. Here their atomic and magnetic structures are investigated using neutron powder diffraction. Neutron powder diffraction (NPD) is the most advantageous technique for using the RM due to the simple peak shape produced by the relatively coarse resolution of neutron diffractometers. Powder diffraction is a scientific technique using X-Ray or neutron diffraction on powder or microcrystalline samples for structural characterization of materials. We start with a brief description of how powder neutron diffraction experiments are conducted, including some (but not too much) of the underlying physics and math that enable this technique. High-pressure synthesized quasi-one-dimensional NaMn 2 O 4 and Li 0.92 Mn 2 O 4 are both antiferromagnetic insulators. Specifically, we will focus on powder neutron diffraction.