On the Debye temperature in sigma-phase Fe-V alloys

A series of sigma-phase Fe_{100-x}V_x samples with 34.4 < x < 59.0 were investigated by neutron and X-ray diffraction and Mossbauer spectroscopy (MS) techniques. The first two methods were used for verification of the transformation from alpha to sigma phase and they also permitted to determine lattice parameters of the unit cell. With MS the Debye temperature, T_D, was evaluated from the temperature dependence of the centre shift, , assuming its entire temperature dependence originates from the second-order Doppler shift. To our best knowledge, it is the first ever-reported study on T_D in sigma-FeV alloys. Both attice parameters i.e. a and c were revealed to linearly increase with x. T_D shows, however, a non-monotonic behaviour as a function of composition with its extreme values between 425K for x=40 and 600K for x=59. A local maximum of 525K was found to exist at x=43

Synthesis, X-Ray, Neutron and Magnetic Studies of New In-Plane Anisotropy M-Hexaferrites BaFe12-2xAxMexO19 (A = Ru, Ir ; Me = Co, Zn)

Ti-Co substituted M-hexaferrites have been extensively investigated as promising materials for magnetic recording or microwave devices. Doping BaM hexaferrite with Ru-Me or Ir-Me (Me = Zn, Co), compounds are obtained with much higher Tc and Ms values than with Ti-Co elements. Powders and single crystals of BaFe12-2xAxMexO19 have been prepared. Magnetization measurements have been performed on single crystals at room and liquid helium temperatures, and magnetic anisotropy constants K1 and K2 calculated. Precise crystal structures of substituted compounds have been determined by X-ray diffraction, and cation distribution on all crystallographic sites refined. Magnetic structures of (Ru-Co)x and (Ir-Zn)x substituted hexaferrites with x = 0.3 and 0.8 have been determined by using neutron diffraction. According to these studies, magnetic anisotropy change is correlated with the substitution of A for Fe cations on bipyramidal and octahedral sites in the R block, and Me for Fe cations on tetrahedral and bipyramidal sites. Magnetic moments rotate progressively with x from the c-axis to the (a, b) plane

Spin-lattice coupling induced phase transition in theS=2 frustrated antiferromagnet CuMnO₂

The crystal and magnetic structures of the layered oxide crednerite CuMnO2 have been studied by neutron powder diffraction. In this system, which is topologically representative of a frustrated square lattice with nearest (J1) and diagonal next-nearest- (J2) neighbor interactions, three-dimensional antiferromagnetic ordering is observed below TN=65 K, with propagation vector k1=(−1/21/21/2). Frustration is relieved through a strong magnetoelastic coupling to the lattice, evidenced by a structural phase transition from a monoclinic (C2/m) to a strained triclinic C1̅ phase as magnetic order sets in. The magnetic order observed, which is described as spins antiferromagnetically aligned along [1-1 0] and ferromagnetically aligned along [1 1 0], corresponds to the so-called collinear antiferromagnetic order predicted for a frustrated two-dimensional antiferromagnetic Heisenberg model on a square lattice for J2/J1>0.5 in the presence of spin-lattice coupling