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MnCl2(urea)2 is a new linear chain coordination polymer that exhibits slightly counter-rotated Mn2Cl2 rhomboids along the chain-axis. The material crystallizes in the noncentrosymmetric orthorhombic space group Iba2, with each Mn(II) ion equatorially surrounded by four Cl- that lead to bibridged ribbons. Urea ligands coordinate via O atoms in the axial positions. Hydrogen bonds of the Cl···H-N and O···H-N type link the chains into a quasi-3D network. Magnetic susceptibility data reveal a broad maximum at 9 K that is consistent with short-range magnetic order. Pulsed-field magnetization measurements conducted at 0.6 K show that a fully polarized magnetic state is achieved at Bsat = 19.6 T with another field-induced phase transition occurring at 2.8 T. Zero-field neutron diffraction studies made on a powdered sample of MnCl2(urea)2 reveal that long-range magnetic order occurs below TN = 3.2(1) K. Additional Bragg peaks due to antiferromagnetic (AFM) ordering can be indexed according to the Ib′a2′ magnetic space group and propagation vector τ = [0, 0, 0]. Rietveld profile analysis of these data revealed a Néel-type collinear ordering of Mn(II) ions with an ordered magnetic moment of 4.06(6) μB (5 μB is expected for isotropic S = 5/2) oriented along the b-axis, i.e., perpendicular to the chain-axis that runs along the c-direction. Owing to the potential for spatial exchange anisotropy and the pitfalls in modeling bulk magnetic data, we analyzed inelastic neutron scattering data to retrieve the exchange constants: Jc = 2.22 K (intrachain), Ja = −0.10 K (interchain), and D = −0.14 K with J > 0 assigned to AFM coupling. This J configuration is most unusual and contrasts the more commonly observed AFM interchain coupling of 1D chains. [ABSTRACT FROM AUTHOR]

The interplay between the crystalline and magnetic structures of a 4% Cr-doped Bi0.37Ca0.63Mn0.96Cr0.04O2.99 has been investigated by alternating current (ac) magnetic susceptibility, electrical resistivity, and neutron diffraction measurements. The compound crystallizes into a monoclinic P21/m symmetry. A Jahn-Teller distortion occurs at 280 K. The thermal behavior of charge transport may be described by a three-dimensional variable range hopping conduction. Strong interplay between the localized magnetic electrons and the itinerant electrons are clearly revealed as the localization length increases by 20% when the Mn spins become ordered below 85 K. Short range magnetic correlations persist up to 160 K. The collinear magnetic structure can be viewed as consisting of ferromagnetic spintrimers antiferromagnetically embedded in a ferromagnetic environment. Cr-doping reduces the charge ordering temperature and the magnetic ordering temperature. It nevertheless introduces long.range ferromagnetism. [ABSTRACT FROM AUTHOR]

The crystal and magnetic structures of antiperovskite compounds Mn3SnC, Mn3Sn0.95C0.9, and Mn3Sn0.93Si0.07C0.94 were studied as a function of temperature and magnetic field by neutron powder diffraction. For Mn3SnC, the magnetic field induces a dramatic variation of antiferromagnetic moment and lattice parameter. Because of this spin-lattice coupling, the "square" antiferromagnetic (AFM) structure plays a key role in inducing a negative thermal expansion in the material. Moreover, the thermal expansion parameter is closely related to the rate of change of the AFM moment, which can be controlled by introducing vacancies or by doping. The variations of the AFM moment and lattice parameter in Mn3SnC with magnetic field make it possible to use the tunable properties for technical applications.