S. Baran

Antiferromagnetism of ternary lanthanide stannides RAuSn (R = Pr, Nd, Gd - Er)

Neutron diffraction and magnetometric data show that hexagonal (LiGaGe-type crystal structure) RAuSn compounds (R = Pr, Nd, Gd, Tb, Dy, Ho) order antiferromagnetically at low temperatures. Their magnetic structures are described by the wavevector ; the magnetic moments are normal to the hexagonal axis in TbAuSn and DyAuSn, parallel to it in PrAuSn and HoAuSn and make an angle of in NdAuSn. ErAuSn is cubic (space group ). At T = 1.6 K only a broad peak corresponding to short-range ordering is observed. The observed Neel points range from 2.8 K in PrAuSn to 24 K in GdAuSn. In all title compounds the magnitudes of ordered magnetic moments at 1.6 K derived from neutron diffraction experiments are smaller than the respective free ion values, indicating a strong effect of the crystalline electric field.

Magnetic phase transitions in TbRhSn

The magnetic ordering of TbRhSn, crystallizing in the hexagonal ZrNiAl-type structure, has been investigated by high-resolution neutron diffractometry in the temperature range between 1.7 and 23.9 K. Tb in TbRhSn has been found to order magnetically below 19 K. Its magnetic structure corresponds to propagation vector ~ ¼½ 1 ; 0; 1 � ; and by a new group-theoretical analysis is shown to be based on the two irreducible representations t2 and t4: This model also explains the change of magnetic ordering at Tt ¼ 11 K: New aspects of bulk magnetic measurements are also reported. Moreover, our results are compared with previously published data. r 2003 Elsevier Science B.V. All rights reserved.

Magnetic structures of RNixSn2 (R=Tb, Ho) compounds

Abstract The magnetic structure of 1:1:2 stannides, determined on the basis of powder neutron diffraction data, is reported. The RNi x Sn 2 (R=Tb, Ho) compounds crystallize in the orthorhombic CeNiSi 2 -type structure. Magnetic and neutron diffraction measurements show that both compounds are antiferromagnets with Neel temperatures of 17.4 K for R=Tb and 6.6 K for R=Ho. 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 RNi x Sn 2 are compared with those observed in RNiSn 2 and the isostructural silicides and germanides.

Magnetic properties of RAuSn compounds

Abstract Neutron diffraction and magnetometric data show that RAuSn compounds (R=Gd–Ho) with the hexagonal LiGaGe-type crystal structure order antiferromagnetically at low temperatures. Their magnetic structures are described by the wave vector k =[1/2,0,0]; the magnetic moments are normal to the hexagonal axis in TbAuSn and DyAuSn and parallel to it in HoAuSn. ErAuSn is cubic (MgAgAs-type of crystal structure). The long range magnetic ordering is not observed at T =1.6 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.

Magnetic order in RAgGe (R=Gd–Er) intermetallic compounds

Abstract Polycrystalline samples of the ternary intermetallics RAgGe (R=Tb–Er) were investigated by means of magnetization and neutron diffraction measurements. For GdAgGe compounds only magnetic measurements were performed. They crystallize in the hexagonal ZrNiAl-type structure. Magnetic measurements show antiferromagnetic ordering at Neel temperatures between 15.6 K for R–Gd and 3.6 K for R=Er. For TbAgGe the neutron diffraction data reveal a complicated sine modulated magnetic structure which is affected by temperature changes. For DyAgGe and HoAgGe the square modulated magnetic ordering is described by the wave vector k =( 1 3 1 3 0) while for ErAgGe by k =( 1 2 1 2 0). With increasing number of 4f-electrons one observes a change of the direction of magnetic moment from parallel to the c -axis for R=Tb via one which forms an angle ϕ with the c -axis for R=Dy, to one which lies in the basal plane for R=Ho and Er.

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 properties of PrPdSb and NdPdSb compounds

Magnetometric and neutron diffraction measurements performed for PrPdSb and NdPdSb (hexagonal, LiGaGe-type crystal structure) indicate the absence of any long-range magnetic order in PrPdSb at 1.5 K and a sine-modulated order in NdPdSb described by the wave-vector , stable below the Neel point at 10 K. The magnetic moment of is localized on the Nd ion. Below , additional magnetic reflections appear pointing at a square-modulated magnetic structure. The magnetic moment at 1.67 K is . In both magnetic phases of NdPdSb the moments are parallel to the hexagonal c-axis.

Magnetic Properties of the Nanocrystalline DyMnO_{3} Compound

V. Dyakonov, A. Szytuła, S. Baran, Z. Kravchenko, E. Zubov, O. Iessenchuk, W. Bazela, M. Dul, A. Zarzycki and H. Szymczak Institute of Physics, PAS, al. Lotników 32/46, 02-668 Warsaw, Poland A.A. Galkin Donetsk Physico-Technical Institute, NANU, R. Luxembourg St. 72, 83114 Donetsk, Ukraine M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059, Kraków, Poland Institute of Physics, Technical University, Podchorążych 1, 30-084 Kraków, Poland

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.