Z. Tomkowicz

Magnetic transition in TbMn2Si2

Abstract TbMn2Si2 (ThCr2Si2-type crystal structure) exhibits at 1.6 K two ferromagnetic sublattices composed of Tb1− and Mn2− magnetic moments directed along thec-axis; their magnitudes at 1.6 K are 8.7(1) and2.4(1)μR respectively. The sublattices are oriented antiferromagnetically. The Tb sublattice becomes disordered at 100 K: the Mn sublattice starts to transform into an antiferromagnetic structure at 100 K and is stable with2.4(1)μR moment up to the Neel point at 501 K.

Magnetic structures of RCuGe (R = Pr, Nd, Tb, Dy, Ho and Er) compounds from neutron diffraction and magnetic measurements

Abstract The crystal and magnetic structures of RCuGe (R = Pr, Nd, Tb, Dy, Ho and Er) compounds were determined by neutron diffraction on polycrystalline samples. Their magnetic data, including also GdCuGe, are reported. The compounds with R = Pr and Nd have hexagonal AlB 2 -type crystal structure, while other compounds show hexagonal LiGaGe-type. All compounds are antiferromagnetic at low temperatures. The Neel temperatures change from 2.2 K for R = Pr to 17 K for R = Gd. The magnetic structures of these compounds (excluding NdCuGe) are sine modulated with wavevector k = ( 1 3 ,0,0) . For heavy lanthanide compounds a change in direction of the magnetic moments, from perpendicular to the c -axis (R = Tb and Dy) to parallel to the c -axis (R = Ho and Er), has been found. For ErCuGe a change in magnetic structure is observed at low temperatures. NdCuGe exhibits a collinear antiferromagnetic structure with unit cell dimensions a m = √(3 a h ), b m = a h , c m = c h and magnetic moments parallel to the a -axis.

Incommensurate-commensurate magnetic phase transition in TbCuSn

Abstract TbCuSn (hexagonal, LiGaGe-type crystal structure) exhibits at 1.5 K a magnetic ordering described by the wave vector k =[ 1 2 , 0, 0] with moments aligned along the b-axis. At 12.6 K an additional incommensurate sine modulated ordering appears ( k =[0.45, 0, 0] ) with magnetic moments aligned also along the b-axis. The Neel point of TbCuSn has been determined to be at 15.3 K.

Magnetic structure of NiMnGe

Abstract NiMnGe is antiferromagnet with a Neel temperature T N = 346 K. Additional magnetic phase transition is observed at T t = 185 K. On the basis of neutron diffraction a spiral magnetic structure was established. The phase transition at T t is connected with the reorientation of the spiral axis.

Mössbauer and magnetic investigations of YBa2Cu3O7 superconductors

Abstract The d.c. electric resistivity, static and a.c. magnetic susceptibility as well as Mossbauer effect methods have been employed to study properties of YBa 2 Cu 3 O 7 superconductors. Substitution of 0.1 at .% of Cu atoms by 57 Fe atoms was found to have no noticeable influence on electric and magnetic properties of the investigated sample. The a.c. magnetic susceptibility method has indicated an energy dissipation of the a.c. magnetic field inside the investigated samples while the Mossbauer effect method has indicated the distribution of an electric field gradient at the Cu-II positions caused by a disorder of oxygen vacancies. The transition to the superconducting state does not change an electronic configuration of the 57 Fe atoms.

Magnetic structures of RCuGe (R = rare earth) compounds

Abstract The crystal and magnetic structures of RCuGe (R = Pr, Nd, Tb, Dy, Ho and Er) compounds were determined by neutron diffraction on polycrystalline samples. Their magnetic data along with those for GdCuGe are reported. The compounds with R = Pr and Nd have the hexagonal AlB2-type crystal structure, while other compounds represent hexagonal LiGeGa-type. All compounds are antiferromagnetic at low temperatures. The Neel temperatures change from 1.8 K for R = Pr to 17 K for R = Gd. The magnetic structure of these compounds is sine modulated with the wave vector k = [ 1 3 , 0, 0] (except NdCuGe in case of which k = [ 1 2 , 0, 0] ). For heavy lanthanide compounds, the change of direction of the magnetic moments from the one perpendicular to the c-axis (R = Tb and Dy) to the one parallel (R = Ho and Er) has been found. For ErCuGe, the change of magnetic structure is observed at low temperatures.

Magnetic phase transition of Mn1.88Cr0.12Sb

Abstract The nature of the first order phase transition in Mn1.88Cr0.12Sb crystal is discussed. According to the magnetic susceptibility χ⊥ and the specific heat measurements, there are two phase transitions, at 280 K and 315 K, respectively. They correspond to the vanishing of the “magnetic soft modes” for FIM and AF phases [4]. No change of the energy level positions was detected using the ESCA method.