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The magnetic order disorder of the Cr moments in the antiferromagnetic state of the ferrimagnet NiCr2O4 is reinvestigated by neutron powder diffraction to clarify the observation of reduced Cr moments located on a pyrochlore like lattice [M. Reehuis et al., Phys. Rev. B 91, 024407 2015 ]. The change of the spin structure in the slightly Cu doped chromite Ni0.98Cu0.02Cr2O4 has been studied as well, where orthorhombic lattice distortions become stronger. For both chromites we observe at 2 K two magnetic phases one with two propagation vectors k 0,0,1 and 0,0, kz , and a second one with k 1 2,1 2,1 2 . The latter phase disappears at 21 K for NiCr2O4 and at 24 K for Ni0.98Cu0.02Cr2O4. Data analysis shows that the two phases reside on two disparate Cr sublattices. These are identified by different chain directions of strongly bonded spin pairs along diagonals in the pseudotetragonal a 1 a 2 plane. The less distorted NiCr2O4 shows the same subdivision of the lattice still with a saturated Cr moment for the 0,0,1 0,0,kz phase, however, with a strongly reduced moment for the 1 2,1 2,1 2 phase, whereas an almost saturated moment shows up in the Cu doped chromite. The reduced moment in NiCr2O4 indicates disorder on one Cr sublattice down to low temperature due to stronger frustration on the less distorted tetragonal pyrochlore lattice. Magnetoelastic effects and further neighbor spin interactions are mainly considered in the discussion of the observed peculiar ordering processes. Notable is the transition temperature of the 1 2,1 2,1 2 phase of NiCr2O4 around 21 K, where anomalies for the specific heat and for the magnetodielectric behavior have recently been reported [T. D. Sparks et al., Phys. Rev. B 89, 024405 2014 ]

Magnetocaloric (MCE) effect has been studied in the ferromagnetic (FM) GdNi 4 Al, GdNi 4 Si, and the antiferromagnetic (AFM) NdNiAl 4 compounds. All the compounds order magnetically between 9 and 30 K. The maximum magnetic entropy change −Δ S M is in the range of 10–16 J kg −1 K −1 for the studied R Ni 4 M compounds. Arrott plots suggest that the phase transition in GdNi 4 Al and GdNi 4 Si may be of a first order-type. It is ascribed to a field-induced AFM–FM transition. Neutron diffraction experiments on NdNiAl 4 show that its magnetic structure is not of a simple AFM-type. Additionally, the specific heat measurements for NdNiAl 4 reveal a change of the sign of MCE and very small values of −Δ S M and the adiabatic temperature change Δ T ad .

Magnetic properties, including magnetic structure, of some RTIn compounds (R = Tb‐Er; T = Cu, Ni, Pd, Pt, Au) with the hexagonal ZrNiAl-type crystal structure are reported. Distribution of the rare earth atoms in the basal plane is similar to the kagome-lattice. Magnetic moments are localized exclusively on the rare earth atoms and form dierent types of magnetic ordering. Experimental results are analyzed within the Ruderman‐Kittel‐Kasuya‐Yosida and crystal electric field frames. Monte Carlo simulations, including the J1 and J2 exchange integrals between nearest and next nearest spins and Dzialoshinsky‐Moriya interaction, were performed resulting in a number of magnetic phases, some of which are in good agreement with the magnetic ordering determined in the neutron diraction experiments.

The crystal and magnetic structures of the R 2 CuIn 3 (R=Tb,Dy,Ho and Er) compounds have been studied by X-ray and neutron powder diffraction. Moreover, the bulk magnetic properties have been investigated by magnetometric methods. All these compounds crystallize with the hexagonal CaIn 2 -type structure. At low temperatures they order antiferromagnetically with the Neel temperatures in the range from 37.6 K to 3.3 K found for R=Tb and Er, respectively. The magnetic structures can be described by the propagation vectors k = ( k x , k x , 0 ) with the value of k x varying with increasing number of 4f electrons.

Magnetization, magnetic susceptibility, neutron diffraction and X-ray photoemission spectroscopy measurements were performed on polycrystalline samples: PrCo 0.85 Ge 2 and NdCo 0.82 Ge 2 , crystallizing in an orthorhombic structure of the CeNiSi 2 -type. The magnetometric data indicate that both compounds are antiferromagnetic at low temperatures, PrCo 0.85 Ge 2 below 5 K and NdCo 0.82 Ge 2 below 2.1 K. The neutron diffraction data indicate an antiferromagnetic structure in PrCo 0.85 Ge 2 at 1.5 K and give no evidence of any magnetic ordering in NdCo 0.82 Ge 2 . The X-ray photoemission data indicate that the valence bands are formed predominantly by R 4f5d6s and Co 3d bands. The spin-orbit splitting values determined from the Pr and Nd, 3d 5/2 and 3d 3/2 XPS spectra are equal to 20.9 eV for the Pr compound and 23.0 eV for the Nd compound. The analysis of these spectra performed on the basis of the Gunnarsson–Schonhammer model revealed a small hybridization between 4f-electrons of the rare earths with the conduction band which implies rather good stability of the f shell in these compounds.

The cubic CeNi4Mn compound has been claimed to show a large spin-polarization, magnetic moment and a high Curie temperature. To verify these properties we have carried out the magnetometric and neutron diffraction experiments on the nominally polycrystalline CeNi4Mn and YNi4Mn compounds. The real stoichiometry was estimated based on X-ray photoemission and neutron diffraction as CeNi4.2Mn0.8 and Y0.7Ni4.2Mn0.8. The magnetic properties of Y0.7Ni4.2Mn0.8 have been studied with neutron diffraction to investigate the role of the rare earth in CeNi4.2Mn0.8. We have found that the samples crystallize in the hexagonal CaCu5-type of structure. The deviation from the cubic structure is ascribed to the presence of a small nonstoichiometry. These structural changes are accompanied by a drop of the magnetic parameters. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The TbRu 2-x Pd x Si 2 series of solid solutions (x = 0.25, 0.5, 0.75, 1.0, 1.5 and 1.75) was studied by neutron powder diffraction. They crystallize in the body-centered tetragonal ThCr 2 Si 2 -type structure. Analysis of the magnetic component of the neutron diffraction patterns shows the change of the magnetic structure from a sine-modulated LSW II-type for x ≤ 1.0 to a short-range magnetic order for x = 1.5 and a sine-modulated LSW IV-type for x=1.75. In the LSW II-type structure the Tb-moments are parallel to the c-axis while for the LSW IV-type they are parallel to the a-axis. With increasing x a sharp decrease in the Neel temperature is observed. For 0.75 ≤ x < 1.0 two magnetic phases coexist.

The crystal and magnetic structure of Ho2NiGe6 was studied by powder neutron diffraction. The paramagnetic neutron diffraction data confirmed the Ce2CuGe6-type crystal structure reported earlier for this compound. Below the Neel temperature equal to 11 K the Ho magnetic moments form a uniaxial antiferromagnetic ordering. The Ho magnetic moments equal to 8.16 ( 7 ) μ B at 1.5 K are parallel to the b -axis. The data are compared with those published for HoNi0.46(6)Ge2.

The work presents results of magnetometric, transport, XPS and neutron diffraction measurements performed on polycrystalline samples of Ce3Ag4X4 (X=Ge, Sn). The X-ray and neutron diffraction data indicate that these compounds crystallize in an orthorhombic structure of the Gd3Cu4Ge4-type. The magnetometric data reveal a ferromagnetic-like behaviour below 10 K in the case of Ce3Ag4Ge4 and a weak antiferromagnetic-like maximum at 9 K for Ce3Ag4Sn4. The neutron diffraction data do not evidence magnetic ordering in any of the two compounds. Temperature variations of the electrical resistivity and thermoelectric power suggest their metallic character. The Ce 3d X-ray photoemission spectra show that both compounds are mixed valence systems. Analysis of the f2 peak weight using the Gunnarsson–Schonhammer theory suggests a hybridization constant of 169 meV for Ce3Ag4Ge4 and 82 meV for Ce3Ag4Sn4. The valence band spectra are dominated by the Ag 4d states contributions. Broad and very weak peaks extending between 0 and 4 eV correspond to the Ce 5d6s2 states.

Magnetization, magnetic susceptibility, X-ray and neutron diffraction measurements down to 1.5 K were performed on polycrystalline RCo x Ge 2 (R = Gd–Er) samples, in which x = 0.4–0.5. All of them crystallize in the orthorhombic structure of the CeNiSi 2 -type. The compounds were found to order antiferromagnetically at low temperatures except for the Tb and Dy samples, in which no magnetic contributions were observed in the neutron diffraction patterns recorded at 1.5 K although transitions are visible in the temperature dependences of the magnetic susceptibility of these compounds. In the case of HoCo 0.4 Ge 2 magnetic order appearing below the Neel temperature of 8 K is described by the propagation vector k = (1/2, 1/2, 0) and for the ErCo x Ge 2 compounds at 1.5 K the structure is described by k = ( k x , k x , 0). The value of the k x component depends on the concentration x .

Magnetization, magnetic susceptibility, electrical resistivity, thermoelectric power, neutron diffraction and X-Ray photoemission spectroscopy measurements were performed on polycrystalline samples of PrAg 2 Ge 2 and NdAg 2 Ge 2 , both crystallizing with a tetragonal structure of the ThCr 2 Si 2 -type. The data indicate that both compounds order magnetically at low temperatures, PrAg 2 Ge 2 at 12 K and NdAg 2 Ge 2 at 2 K. Neutron diffraction data for the latter indicate antiferromagnetic collinear structure described by the propagation vector k =(½, 0, ½) at 1.5 K. Both compounds exhibit metallic-like electrical behavior. The X-Ray photoemission data indicate that the valence bands are formed mainly by the Ag 4d bands. The spin-orbit splitting values determined from the XPS spectra of Pr and Nd, 3d 5/2 and 3d 3/2 , equal 20.5 eV for the Pr compound and 22.7 eV for the Nd compound. The analysis of these spectra performed on the basis of the Gunnarsson-Schonhammer model indicates a weak hybridization of the 4f electrons with the conduction band.

Alloyed ( Mn 1 - x Fe x ) Au 2 ribbons ( x = 0 –0.075) show a complex dependence of magnetization and magnetoresistivity on composition, magnetic field, and temperature. This is associated with the helimagnetism of MnAu 2 and the field-driven transition from helix to fan spin-structure. The threshold field H thr for this metamagnetic transition strongly depends on x. Neutron diffraction shows that the periodicity length of the helix increases with increasing iron contents x 0.075 . For x = 0.05 a transition from the helical ground-state to a collinear ferromagnetic structure takes place at 150 K; for x = 0.075 only a ferromagnetic order is found.

We report on extensive neutron diffraction on single crystalline CeCu 2 ( Si 1 - x Ge x ) 2 to determine the antiferromagnetic order in the regime with low Ge content, initially called A phase due to the unknown origin of the magnetic order. Starting from the x = 0.45 alloy we followed the magnetic order to lower Ge concentrations and to pure CeCu 2 Si 2 . For all Ge concentrations x ⩽ 1 an incommensurate magnetic order with a propagation vector close to τ = ( 0.25 0.25 0.5 ) is observed. The magnetic order is determined by the nesting properties of the Fermi surface.

A neutron diffraction study was performed to study the spiral spin arrangement of RbCuCl3 as a function of temperature and magnetic field. We clearly observe that the spiral lengthens with increasing temperature up to TN = 19.3 K. A shortening of the spiral occurs when a magnetic field is applied within the plane of spin rotation. No change in the propagation vector is observed with the field applied perpendicular to the spin rotation plane. In addition we measured the temperature dependence of the magnetization and close to TN we determine critical exponents β = 0.238(4) and 0.26(1) at zero field and at 13.5 T, respectively.

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.

Powder neutron diffraction and magnetic measurements have been carried out on R2RhSi3 (R=Dy, Ho and Er) compounds at low temperatures. These compounds crystallize in a derivative of the hexagonal AlB2-type structure and are antiferromagnets with the Neel temperatures equal to: 6.3 K for R=Dy, 5.2 K for R=Ho and 5 K for R=Er. Below these temperatures the magnetic order is described by the propagation vector: k =(0,0, 1 2 ) for R=Dy, k =( 1 2 ,0,0 ) for R=Ho and k=(0,0,0) for R=Er. This magnetic order is stable in the temperature range between 1.5 K and the Neel temperature.

Neutron diffraction has been performed to study the spin arrangement of hexagonal CsCuCl3 in the field region below the incommensurate–commensurate phase transition at HIC–C with field in the ab-plane. In zero field the stacked, triangular-lattice antiferromagnet CsCuCl3 has a helical structure incommensurate along the c-direction and the magnetic structure is characterized by q =( 1 3 1 3 ±Q) . In order to analyse the distortion of the spiral by the field we have looked for higher harmonics up to 10th order in q. The second order was found above 6 T and the fourth order showed up above 10 T. No significant magnetic Bragg intensities were observed for other higher harmonics. From these measurements, together with the field-dependent magnetization measured previously, we construct a detailed picture of the spin arrangement. Our main findings are that the spin reduction present in zero field owing to the frustration on the triangular lattice is lifted for spins pointing along the field while the size of the ordered spins opposite to the applied field is reduced even more. In addition spins along H move together and spins opposite to H spread apart.

Powder samples of Zn2x(CuIn)1−xS2 were synthesized by solid state reaction (T=950°C) in sealed evacuated silica tubes. Based on neutron- and X-ray diffraction data structural parameters were determined using the Rietveld method. Samples with 0.4⩽x⩽1 crystallize in the cubic sphalerite-type structure, samples with 0.1⩾x⩾0 crystallize in the tetragonal chalcopyrite-type structure. A miscibility gap was found in the region 0.1

X-ray and neutron diffraction studies as well as magnetization and electrical resistivity measurements of Er1−xYxCo3 compounds were performed. In the Er-rich compounds, , a temperature-induced metamagnetic transition takes place between weak and strong Co magnetic states. In the intermediate concentration region, , below 40 K a spin reorientation was observed. The magnetic structure below the spin-reorientation transition is non-collinear. The Er moments on the 'cubic' sites (6c) are tilted from the c-axis by an angle of about 55°, while those on the uniaxial 3a positions compose a smaller angle, of about 15°. The spin-reorientation transition is accompanied by a large orthorhombic distortion of the hexagonal PuNi3-type crystal structure, which is accounted for by a large anisotropic magnetostriction of the Er sublattice. The distortion parameter varies linearly with x. Its extrapolated value for ErCo3 is about 2 × 10−3. The concentration dependence of both types of magnetic instabilities is depicted in a magnetic phase diagram of the pseudobinary Er1−xYxCo3 system for the low-temperature region.

The results of magnetic and neutron diffraction studies of a new series of intermetallic compounds R 3 T 4 X 4 (R: La–Nd, Gd–Er; T: Mn, Cu; X: Ge, Sn) are presented. These compounds crystallize in the orthorhombic Gd 3 Cu 4 Ge 4 -type structure (space group Immm ). The rare earth atoms occupy two non-equivalent crystallographic positions. All the investigated compounds are antiferromagnets. In the R 3 Mn 4 Sn 4 series the rare earth and the manganese magnetic moments order at different temperatures: the rare earth moments order at 25 K (R: Pr) and 60 K (R: Nd), while the manganese moments order at 300 K (La), 230 K (Pr) and 210 K (Nd). The R 3 Cu 4 Ge 4 compounds are antiferromagnets with Neel temperatures between 23 K (for Tb 3 Cu 4 Ge 4 ) and 5.9 K (for Er 3 Cu 4 Sn 4 ). For Tb 3 Cu 4 Ge 4 , Er 3 Cu 4 Ge 4 , Ho 3 Cu 4 Sn 4 and Er 3 Cu 4 Sn 4 further phase transitions occur below the Neel temperature. The magnetic moments are localized only on the rare earth atoms. The moments located at different crystallographic sites have different values and order at different temperatures. The electronic structure of Gd 3 Cu 4 X 4 (X: Ge, Sn) was studied by X-ray photoemission spectroscopy (XPS). The complex character of the valence band influences the magnetic properties of these compounds.

Polycrystalline sample of NdNiSn compound has been prepared and studied by powder neutron diffraction measurements. NdNiSn crystallizes in the orthorhombic TiNiSi-type structure (space group Pnma). Below the Neel temperature equal to 3.0 K the Nd magnetic moments form an incommensurate sine-wave modulated structure described by the propagation vector k =(0, 0.482(1), 0.248(3)). Magnetic moments equal 2.42(9) μ B lie in the a – b plane and form the angle of 39° with the b -axis.

Neutron diffraction and a.c. susceptibility measurements have been made on the NdMn 1.55 Fe 0.45 Ge 2 compound. Two phase transitions at T t1 =70 K and T t2 =218 K are detected. Neutron diffraction data give evidence that below T t1 , the Nd moments are ordered ferromagnetically while the Mn moments form a canted Fmc-type of structure. At T t1 the sample undergoes a magnetic phase transition into an antiferromagnetic AFmc-type of structure stable down to T t2 . Above T t2 , the AFl-type of structure is observed. At the magnetic phase transition from the Fmc- to the AFmc-type of structure a change of the a -lattice constant is observed. An external pressure up to 10 kbar causes only a decrease of the values of the Nd and Mn magnetic moments.

Powder neutron diffraction measurements have been performed on TbAg2Si2 at low temperatures. The compound crystallize in the tetragonal ThCr2Si2-type crystal structure (space group I4/mmm). Below TN=18 K TbAg2Si2 orders antiferromagnetically with a sine-wave modulated structure characterized by the propagation vector k =(1,0.3249(5),0) . The Tb magnetic moments, equal 8.36(22) μB, are in the basal plane as expected from the positive sign of the B20 parameter of the crystal electric field Hamiltonian.

Polycrystalline sample of Tb3Cu4Si4 compound was prepared and studied by magnetic and powder neutron diffraction measurements. Tb3Cu4Si4 crystallizes in the orthorhombic Gd3Cu4Ge4-type structure (space group Immm). In this structure the Tb atoms occupy two non-equivalent crystallographic positions: 2d and 4e. Below TN equal to 50 K the Tb moment in the 2d site orders and forms a collinear magnetic structure. At the temperature of T t 1 =38 K a transition from the commensurate magnetic structure, described by the propagation vector k 2 =(0, 1 2 ,0) to an incommensurate one, described by the propagation vector k 1 =(0,0.515,0), is observed. Below Tt2 equal to 7 K the Tb moment in the 4e site forms a sine-wave modulated structure described by the propagation vector k 3 =(0.23, 1 2 , 1 2 ).

In this work, the results of magnetic and neutron-diffraction studies of a new series of intermetallic compounds R3Cu4X4 (R=Gd–Er; X=Ge, Sn) are presented. The X-ray and neutron-diffraction data indicate that these compounds crystallise in the orthorhombic Gd3Cu4Ge4-type structure (space group Immm). In this structure, the rare-earth atoms occupy two non-equivalent crystallographic positions: 2d and 4e. The magnetometric and neutron diffraction measurements indicate that the R3Cu4X4 (R=Gd–Er; X=Ge, Sn) compounds are antiferromagnets with Neel temperatures between 23 K for Tb3Cu4Ge4 and 5.9 K for Er3Cu4Sn4. For Tb3Cu4Ge4, Er3Cu4Ge4 and Er3Cu4Sn4, additional phase transitions are observed below the Neel temperature. The neutron-diffraction data indicate that the magnetic moments are localised only on the rare earth atoms. The moments located at different crystallographic sites have different values and order at different temperatures.

Neutron diffraction and magnetometric measurements show that RRhSi (R = Tb, Dy, Ho) are antiferromagnets below the T N = 25 K for TbRhSi, 14.6 K for DyRhSi and 8.5 K for HoRhSi. For TbRhSi and DyRhSi changes in magnetic structure below T N were detected. For HoRhSi only one stable commensurate magnetic structure was observed. The magnetic structure of DyRhSi was determined for the first time. The new high resolution neutron diffraction data permitted to revise the magnetic phase models of the compounds with R = Tb and Ho.

Magnetic properties of the NdMn 2-x Fe x Ge 2 (x = 0.3, 0.4 and 1.0) are investigated by AC magnetic measurements and neutron diffraction. In ambient pressure in compound with x = 0.3 below 200 K the noncollinear magnetic structure is observed. Above this temperature the magnetic moments transform to the collinear one. For x = 0.4 at 1.5 K the Nd magnetic moments form collinear ferromagnetic structure, while Mn moments noncollinear. With increase of the temperature at T = 50 K Nd moment disappears while Mn moments form two different magnetic structures antiferro- (AF) and ferromagnetic (F). The change between AF and F phases is connected with the change of the lattice constants. For x = 1.0 the Mn moments form collinear antiferromagnetic structure stable in the temperature range between 1.5 K and T N = 203 K. For x = 0.3 the external pressure up to 1.5 GPa causes the change of the critical temperature only, while for x = 0.4 induces the change of the magnetic properties from ferro- to antiferromagnetic. For x = 1.0 the Neel temperature increases with increasing external pressure. The above results indicate that in the NdMn 2-x Fe x Ge 2 system, the increase in the iron content is followed by a change in chemical bond that influences the magnetic properties.

The magnetic structures of the monoclinic carbides Tb2Cr2C3, Ho2Cr2C3 and Er2Cr2C3 (space group C2/m) have been investigated by neutron powder diffraction. Below the Neel temperatures TN=49(1), 14.0(5) and 6.8(5) K the magnetic moments of the terbium, holmium and erbium atoms order antiferromagnetically within the monoclinic ac-plane, respectively. In the case of Tb2Cr2C3 the magnetic structure can be described with the propagation vector k =(0 1 0) and it is stable up to the Neel temperature. The magnetic ordering in Ho2Cr2C3 and Er2Cr2C3 is more complex requiring different sets of coexisting wave vectors pertaining to distinct domains and comprising incommensurate regions and lock-in phase transitions. For the erbium compound the low-temperature ordering is described by the coexisting wave vectors k 1 =(0 0 1 2 ) and k 2 =(0 1 0) and both are stable up to Tt=5.5(3) K. Between 4.5(3) K and TN=6.8(5) K a sine-wave modulated structure with k 3 =(τ x ,0, 1 2 −τ z ) appears, where the vector components vary with the temperature. At 5.3 K one obtains τx=0.055(1) and τz=0.070(1). For Ho2Cr2C3 the ordering associated with k 1 =(0 1 1 2 ) is stable between 1.6 K and Tt=12.7(3) K. A second type of ordering appears below TN=14.0(5) K and corresponds to a sine-wave modulated structure with k 2 =(τ x ,0,–τ z ) . The length of k 2 varies from (0.8856, 0, −0.1395) at 13 K to (0.9935, 0, −0.1075) at Tt=10.2(2), where the modulated structure undergoes a transition to a square-wave one manifested by the presence of higher harmonics.

Ternary Tb 2 CuGe 3 intermetallic compound is investigated by means of neutron diffraction and low-temperature magnetization measurements. This compound is an antiferromagnet with the Neel temperature equals 19.5 K. At 1.5 K the Tb magnetic moments equal 8.73(17) μ B and lie in a – b plane and form a sine-wave modulated structure. This type of the magnetic ordering is stable up to the Neel temperature. This result is in contradiction with the results obtained from macroscopic method which suggest the multiple magnetic transitions and anomalous magnetism in this compound [Solid State Commun. 117 (2001) 645].

WepresentaneutronpowderdiffractionstudyonTmCuAl,crystallizingintheZrNiAl-typehexagonalstructure.OurdataconfirmmagneticorderingbelowT c ¼ 1:9K.Themagneticstructureisalongitudinalspinwavedescribedbyapropagationvectork ¼ð 12 0qÞ withTmmagneticmomentsalongthec-axis.Inadditiontothat,acommensurateantiferromagneticcomponentwithinthebasalplanewithk ¼ð 12 02Þ developsbelowthemagneticphasetransitionatT 1 D1:2K. It leads to a rather complex magnetic structure below T 1 : One-third of the thulium moments has aconsiderablyreducedmagnitudecomparedtotheremainingones.Nofurtherphasetransitionswereobserveddownto50mK.r 2002ElsevierScienceB.V.Allrightsreserved. PACS: 75.25.+z;75.30. m;61.12.LdKeywords: Magneticstructures;Neutrondiffraction;Rare-earthintermetallics 1. IntroductionTheternaryRCuAl(R=rareearth)compoundscrystallize,exceptforLaCuAl,intheZrNiAl-typehexagonal structure (space group P-62m). Pre-viousstudiesrevealedaferromagneticorderingforthe compounds containing the heavy rare-earth(Gd–Er)[1,2].Onthecontrary,anantiferromag-neticbehaviorwasfoundinCeCuAl[3],PrCuAland NdCuAl [4]. The magnetic properties ofTmCuAlremainunclear.Nomagneticorderdownto 1.8K was found in Ref. [1], while magneticordering below 1.9K and a possible additionalphase transition at lower temperatures are re-ported in Refs. [5,6]. The negative Curie–Weissconstantandamaximuminthemagneticsuscept-ibilitysuggesttheimportanceofantiferromagneticinteractions in this compound. The

RNiSn2 (R=Tb, Dy, Ho) compounds crystallize in the orthorhombic LuNiSn2-type structure. Magnetic and neutron diffraction measurements show that all compounds are antiferromagnets with the Neel temperature 5.2 K for R=Tb, 6.5 K for R=Dy and 2.2 K for R=Ho. Neutron diffraction data indicate the presence of a complex magnetic order. In TbNiSn2 and DyNiSn2 the rare earth moments form noncollinear magnetic structure while in HoNiSn2 the Ho moments form a collinear antiferromagnetic structure described by the Az mode with a different magnitude of the magnetic moment in each sublattice.

In this paper, we present the results of a neutron-scattering study on a single crystal of UNi2Si2. This material crystallizes in the tetragonal ThCr2Si2-type structure and orders antiferromagnetically (AF) at TN=125 K. Below TN, it exhibits three different AF phases in zero magnetic field. The phases are strongly anisotropic with the U moment parallel to the c-axis, forming ferromagnetic basal planes. Between TN and 108 K, the incommensurate AF1 phase with q =(0,0,q z ) is established (qz∼0.74). The intermediate phase AF2, between 108 and 40 K, is of the AF-I type with q =(0,0,1) and the ground-state phase AF3 is an uncompensated squared-up AF structure with (+ + −) stacking of the basal planes along the c-axis ( q =(0,0,2/3) ). Both the 108 and 40 K transitions are of the first order. The complex magnetic phase diagram of UNi2Si2 was studied in horizontal magnetic fields parallel to the c-axis up to 6 T. Above TN, the critical scattering was studied in zero field.

Neutron powder diffraction and magnetometric studies of the HoRh2-xPdxSi2 series of solid solutions (x = 0, 0.5, 0.75, 1.0, 1.5, 1.8) are reported. The intermetallics investigated crystallize in the body-centred-tetragonal ThCr2Si2-type structure (space group I4/mmm). All the samples order antiferromagnetically at low temperatures. For low values of the dilution parameter x a simple collinear antiferromagnetic structure of the AFI type is stable. Below TN the magnetic moments are parallel to the c-axis and then, below Tt, deflect forming an angle with the c-axis. Further replacement of Rh by Pd results in the development of a sine-wave-modulated magnetic structure with one two-component propagation vector and magnetic moments in the basal plane. For x = 1.8 a sine-wave-modulated structure similar to that reported for HoPd2Si2 (i.e. with a two-component propagation vector and magnetic moments parallel to the b-axis) was found.

Neutron diffraction investigations have been performed to study the magnetization process of CsCuCl3 with the magnetic field aligned within the ab-plane. In zero field the stacked, triangular-lattice antiferromagnet (TLA) CsCuCl3 has a helical structure incommensurate in the chain direction normal to the ab-plane. The magnetic phase diagram was investigated from 2 K up to TN in fields up to 17 T. The phase line for the expected incommensurate-commensurate (IC-C) phase transition could be determined throughout the whole phase diagram. At low temperature the IC-C transition is roughly at half the saturation field HS. The neutron diffraction patterns were found to be well described by a sinusoidally modulated spiral in fields up to HS/3. The initial increase of the scattering intensity in rising field indicates a continuous reduction of the spin frustration on the triangular lattice. Between HS/3 and HS/2 a new phase occurs where the spiral vector has a plateau in its field dependence. Close to the IC-C transition a growing asymmetry of magnetic satellite-peak intensities indicates domain effects which are related to the lifting of the chiral degeneracy in the ab-plane in rising field. The phase diagram obtained has some similarities with those calculated for stacked TLAs by considering the effects of quantum and thermal fluctuations.

An adjustable in-pile fan collimator was built and tested in a neutron diffraction set-up with a large horizontally curved monochromator for focusing in real and reciprocal space. For small samples, enhancements of intensity up to a factor of five without losing 2θ-resolution are possible in comparison to a conventional diffractometer equipped with Soller-type collimators. Our geometry will be discussed and compared to both the conventional diffractometer and a focusing arrangement using an in-pile diaphragm.

Polycrystalline samples of the RAuIn (R=Tb, Dy, Ho) compounds have been prepared and studied by powder neutron diffraction and magnetisation measurements. These compounds crystallise in the hexagonal ZrNiAl-type structure. They have been found to be antiferromagnets with the Neel temperatures equal: 35 K (R=Tb), 11 K (R=Dy) and 4.8 K (R=Ho). At T=1.5 K the magnetic ordering of TbAuIn and DyAuIn is described by the propagation vector k=(0, 0, 1 2 ) while in the case of HoAuIn by two propagation vectors: k1=(0, 1 2 , 1 2 ) and k2=(0, 0, 1 2 ). Between TN and TSG=58 K spin-glass behaviour is reported for TbAuIn. For the first time, the two-step magnetic phase transition: From the long-range antiferromagnetic order through a spin-glass-like short-range ordering to a paramagnetic state is experimentally evidenced in this compound.

Polycrystalline sample of the ErRhSi compound have been prepared and studied by powder neutron diffraction, specific heat and electrical resistivity measurements. This compound crystallizes in the orthorhombic TiNiSi-type structure. The magnetic phase transition at Tt=2.3 K and the Neel temperature TN=8.5 K have been determined by the temperature dependencies of the intensities of the magnetic peaks, specific heat and electrical resistivity. At 1.5 K a commensurate magnetic structure, described by the propagation vector k = (0 1 2 0) coexists with the incommensurate one with k =(0,0.4184(4),0) . Above Tt only incommensurate phase with the propagation vector k =(0,0.4173(2),0) at 4 K exist. Er magnetic moment is parallel to the a-axis for both phases below Tt and form angle ±19° with a-axis in the temperature range Tt and TN.

Polycrystalline samples of Ce 2 Co 1− x Au x Si 3 for x equal to 0.4, 0.6, and 0.8 have been studied by neutron diffraction. All compounds exhibit the hexagonal crystal structure derived from the AlB 2 -type. For x =0.4 the Ce magnetic moments equal to 0.6(1) μ B form a simple antiferromagnetic structure and are parallel to the b -axis. In Ce 2 Co 0.2 Au 0.8 Si 3 a short-range magnetic order is observed. For x =0.6 the Ce-moments do not order up to 1.5 K.

The magnetic structures of HoAuGe and ErAuGe, both crystallizing in the hexagonal LiGeGa-type structure, have been investigated by high resolution neutron diffractometry in the temperature range between 1.5 and 7.7 K. For ErAuGe, additional low temperature diffraction experiments have been performed between 40 mK and 1.4 K. Both compounds order antiferromagnetically at low temperatures. The magnetic structure of HoAuGe at 1.5 K is described by a propagation vector k =[ 1 2 , 0, 0] . The low temperature diffraction pattern of ErAuGe is similar to that obtained for HoAuGe, however, some magnetic reflections of ErAuGe show a significant broadening. This broadening is due to a magnetic domain size effect. Transversal sine wave incommensurate magnetic structures appear close to the Neel temperatures. These structures can be described by a propagation vector k =[0.4461(5),0,0] at 4.5 K for HoAuGe and k =[0.4185(40),0,0] at 3.0 K for ErAuGe.

Dependent on sample preparation ErAuSn crystallizes in an either cubic or hexagonal structure. The magnetic structure of polycrystalline cubic ErAuSn has been investigated by neutron diffraction between 40 mK and 3.6 K. The magnetic propagation vector was found to be k =[ 1 2 , 1 2 , 1 2 ] and the Neel temperature was determined to be 1.3(2) K.

Neutron diffraction, specific heat and magnetization measurements were applied to study the magnetic structures in Mn0.88Fe0.12WO4 using single crystal and powder samples. A commensurate antiferromagnetic structure with a propagation vector k = (1/4,1/2,1/2) below 13.5 K and an incommensurate structure with k = (0.23,0.5,0.508) between 13.5 K and 15.5 K were found to be the dominating ordered states. The temperature behaviour of the propagation vector above the IC-C phase transition shows a logarithmic behaviour. An FeWO4-type ordering of spins with k≈(1/2,0,0) is observed below 19 K and coexists between 15.5 K and 13.5 K with the MnWO4-type structure. Our experimental results indicate a cluster-like FeWO4-type magnetic ordering on a diluted 3D lattice, which interpenetrates the dominating MnWO4-type spin ordering. Below 13 K, with the majority of spins ordered in the commensurate MnWO4-type structure, reflections which can be indexed to a unit cell doubled along the crystallographic a-axis appear again; however, these intensities cannot purely be related to Bragg diffraction by ordered local magnetic moments at the (Mn, Fe) positions.

In the past only powder diffractometers with medium resolution were available at BENSC. To satisfy ademand from the user community for crystal structure refinements using the Rierveld method, a new high-resolution powder diffractometer has been installed at the BER2 reactor and it came into user operation during the second half of 1999. The instrument is designed for investigating crystal structures with cell volumes up to 1000 k3 by profile refinements of powder diffractograms. Data sets of sufficient resolution and statistics depenlng on the complexity of the structure are needed to apply the Rietveld method successfully. To fulfill these demands, it was decided to build an instrument based on a classical angular dispersive diffractometer similar to the D2B at the ILL however, with relaxed collimations considering the lower thermal flux at the BER2 compared to the ILL reactor. Beside the standard setting with a take-off angle at the monochromator above 90°, the instrument allows to vary the tak...

Continuing our neutron diffraction experiments in the external fields up to 14.5 T on the frustrated antiferromagnet CsCuCl 3 , we found two new features: (1) broad central peaks appear in addition to the peaks characterising the two incommensurate phases investigated so far; (2) the spiral vector which has a complicated temperature dependence at low and medium fields becomes temperature independent in high field.

We report the magnetic structure of the recently discovered mass enhanced antiferromagnet UPd 2 Sb , with an antiferromagnetic transition temperature of T N = 55 K . Our results have been obtained by analyzing the difference spectra of neutron scattering experiments carried out at low temperatures of 60 and 1.6 K. Furthermore, the temperature dependence of the antiferromagnetically ordered moment has been determined. The antiferromagnetic phase consists of ferromagnetic planes spanned by two cubic axes of the Heusler lattice, which are antiferromagnetically coupled along the third axis. From a comparison of magnetic and structural peak intensity the ordered moment was determined to μ ord = 1.3 μ B at zero temperature. The antiferromagnetic phase is characterized by a short magnetic correlation length of the order of 100 A, this as result of structural disorder in this compound.

The magnetic structures of the ThCr2Si2 type compounds LnNi2P2 (Ln=Tb, Dy, Ho, Er) were investigated by neutron powder diffraction. In agreement with the previously determined magnetic susceptibility data only the lanthanoid atoms were found to carry magnetic moments. They order antiferromagnetically at TN=10.2(4) K (TbNi2P2), 5.0(4) K (DyNi2P2), 2.5(4) K (HoNi2P2) and 1.9(3) K (ErNi2P2), respectively. The magnetic unit cell of these compounds can be described with the propagation vector k=(1/2, 0, 1/2). The magnetic moments of the terbium, dysprosium and holmium atoms are aligned parallel to the doubled c axis of the tetragonal nuclear cell, whereas the moments of the erbium atoms are ordered perpendicular to this axis and the (one) doubled a axis. Magnetization measurements carried out with a SQUID magnetometer at 2 K show metamagnetic transitions for TbNi2P2 and DyNi2P2.

The nuclear and the magnetic structures of Ho 2 Mo 2 C 3 and Er 2 Mo 2 C 3 have been determined from neutron powder diffraction data. The magnetic properties of both compounds have also been investigated with a SQUID magnetometer. The nuclear structure of both compounds (space group C2/m, Z=2) is similar to that determined earlier for Ho 2 Cr 2 C 3 . The only essential difference arises through the differing location of one carbon position. The magnetic moments of the holmium and erbium atoms order ferromagnetically with Curie temperatures of 13.5(5) and 8.0(5) K, respectively. Chemical bonding in Ho 2 Mo 2 C 3 and Er 2 Mo 2 C 3 is briefly discussed. In both structures the transition metal and carbon atoms form two-dimensionally infinite polyanions, which are separated from each other by the rare earth atoms. The 18-electron rule can only be obeyed for the transition metal atoms if bonding interactions between the rare earth atoms are neglected.