E. Wawrzyńska

Magnetic properties and magnetic structures of RCoxSn2 (R=Gd–Er) compounds

Abstract Magnetic properties of RCo x Sn 2 (R=Gd–Er) stannides, determined on the basis of magnetic and powder diffraction data, are reported. The compounds crystallize in the orthorhombic CeNiSn 2 -type structure. Magnetic and neutron diffraction measurements (the latter for R=Tb and Ho) show that all the compounds are antiferromagnets with Neel temperatures of 16.5 K (R=Gd), 18.8 K (R=Tb), 7 K (R=Dy), 5.6 K (R=Ho) and 4.5 K (R=Er). The neutron diffraction data indicate the presence of collinear magnetic structures described by the propagation vector k =(0, 0, 1 2 ) for R=Tb and k =( 1 2 , 1 2 , 0 ) for R=Ho. The determined magnetic structures of RCo x Sn 2 (R=Tb, Ho) are similar to those observed in the isostructural RNi x Sn 2 .

Magnetic structures of R3Cu4Ge4 (R=Tb, Dy, Ho, Er)

Abstract Neutron diffraction studies of polycrystalline R3Cu4Ge4 (R=Tb, Dy, Ho, Er) intermetallic compounds with the orthorhombic Gd3Cu4Ge4-type crystal structure indicate complex magnetic structures. In these compounds the rare earth atoms occupy two nonequivalent 2d and 4e sublattices. For R=Tb and Er with decreasing temperature the magnetic moments in the 2d sublattice order first; the 4e sublattice magnetic moments order at lower temperatures. For R=Dy, Ho both sublattices order simultaneously although the magnetic moment values are different for each of them. In the compounds with R=Tb and Er a change of the magnetic structure, connected with the 2d sublattice, is observed near the Neel temperature. This is a transition from the commensurate structure, described by the propagation vector k =(0, 1 2 ,0) at low temperatures to the incommensurate structure with k =(0, 1 2 +δ,0) at higher temperatures (still below the Neel temperature).

Magnetic structures of R3Cu4Sn4 (R = Pr and Nd)

Polycrystalline samples of R3Cu4Sn4 (R = Pr and Nd) intermetallics were studied with neutron diffraction methods. Both of them crystallize in the orthorhombic structure of Gd3Cu4Ge4-type. Pr3Cu4Sn4 orders antiferromagnetically below the N?el temperature of about 11?K whereas Nd3Cu4Sn4 does not order magnetically down to 1.5?K. In Pr3Cu4Sn4 the magnetic moments are localized at the Pr atoms that occupy two non-equivalent 2d and 4e sublattices and order simultaneously at the N?el temperature forming a collinear magnetic order along the x-direction.

Commensurate–incommensurate magnetic phase transitions in PrCu2Ge2 and NdFe2Ge2

New neutron diffraction and ac magnetic susceptibility data concerning phase transitions and magnetic structures of PrCu2Ge2 and NdFe2Ge2 are presented here. In the case of PrCu2Ge2 at low temperatures collinear antiferromagnetic ordering of the AFI type is observed. In the temperature range between Tt = 5.5 K and TN = 15.0 K the collinear and a sine wave modulated structure coexist. The latter phase is a long period modulation along the a-axis described by the propagation vector k = (0.0336(5),0,0). In the case of NdFe2Ge2 the situation is similar: a collinear AFII-type low temperature phase (k = (0,0,1/2)) changes into a non-collinear one (k = (0,0,0.46(1))) at about 12 K. In both compounds in all phases magnetic moments localized on rare earth ions are parallel to the c-axes.

Neutron diffraction studies of the magnetic structure of Ho3Pd4Ge4

Abstract Ho 3 Pd 4 Ge 4 crystallizes in the orthorhombic Gd 6 Cu 8 Ce 8 -type of structure (space group Immm ) in which the Ho atoms occupy two nonequivalent crystallographic positions: 2a and 4j . Neutron diffraction measurements indicate that the Ho moments in the 4j site below 6.7 K form a collinear antiferromagnetic structure with the magnetic moments parallel to the a axis, whereas the Ho moments in the 2a site below 5 K form a sine-wave modulated structure with the magnetic moments parallel to the c axis.

Magnetic structures of R2RhSi3 (R=Ho, Er) compounds

Powder X-ray and neutron diffraction and magnetic measurements have been performed on R2RhSi3 (R=Ho and Er) compounds at low temperatures. The compounds crystallize in a derivative of the hexagonal AlB2-type structure. The crystal structure parameters have been refined on the basis of the X-ray and neutron diffraction patterns collected in the paramagnetic region. These compounds are antiferromagnets with Neel temperatures of 5.2 K for Ho2RhSi3 and 5 K for Er2RhSi3. Both compounds exhibit collinear magnetic structures, described by the propagation vector k=(1/2,0,0) for Ho2RhSi3 and k=(0,0,0) for Er2RhSi3. This magnetic order is stable in the temperature range between 1.5 K and the Neel temperature.

Magnetic structure of HoPd2Ge2

Abstract The magnetic structure of HoPd 2 Ge 2 is determined from powder neutron diffraction data. The Ho-moments order below T N =3.8 K in a sine-wave modulated structure with k =(0.546(2), 0, 0.180(2)). Magnetic moments of 7.8(2) μ B at 1.5 K, localized on Ho 3+ ions, form an angle of 43° with the c -axis. Above T N short range magnetic order is observed up to 4.8 K.