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The structure and magnetic properties of Gd2Co17−xCrx (1.17 ≤ x ≤ 3.0) compounds have been investigated by means of X-ray diffraction (XRD) and magnetization measurements. The powder X-ray diffraction patterns show that all samples crystallize as a single phase with the rhombohedral Th2Zn17-type structure. The lattice parameters a and the unit cell volume V increases slightly with increasing Cr content, but the c parameter varies in a less simple way with increasing Cr content. The X-ray diffraction patterns of the magnetically aligned samples show that all compounds investigated have uniaxial anisotropy. Spin reorientation phenomena occur in all of the compounds. The Curie temperature TC, the spin reorientation temperature Tsr, the spontaneous magnetization M0 and the saturation magnetization Ms decrease with the increasing Cr content. The anisotropy constant K1 and the anisotropy field Ba of the compounds at room temperature reach a maximum for x = 1.76. The M0 and Ms increase with increasing temperature from 5 K to 300 K. The easy-axis anisotropy of all compounds changes to easy-plane anisotropy at low temperatures and the spin reorientation phenomena are more pronounced for low Cr concentration.

The magnetization has been measured of single crystals of RMn 6 Ge 6− x Ga x (R = Tb, Er, Tm and Yb and x ≈ 1) compounds at 4.2 K in high magnetic fields up to 65 T applied along the main crystallographic directions. At low temperature, where the magnetocrystalline anisotropy is determined by the R contribution, these compounds exhibit easy-axis anisotropy with the c -axis as preferred moment direction. The magnetization display a variety of field-induced phase transitions which are particularly pronounced in the compounds with Tb, Er and Tm. The Yb compound exhibits the onset of a phase transition in the field region above 65 T. The results are discussed in terms of the interplay between the antiferromagnetic intersublattice R–Mn coupling and the magnetic anisotropy.

DyAl2 nanoparticles have been prepared by means of are discharge in a mixture of argon and hydrogen gas. The Structure of DyAl2 nanoparticles is studied by means of X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron rnicroscopy. X-ray photoelectron spectroscopy shows that the as-prepared DyAl2 nanoparticles are coated with a layer of Al2O3 phase on the surface, and their sizes vary from 20 nm to about 100 nm. The DyAl2 nanoparticles exhibit ferromagnetic properties that are different from bulk DyAl2 compound. The gradual decrease of the magnetization with increasing temperature in a wide temperature range reveals the size distribution ofthe DyAl2 nanoparticles. The magnetic-entropy changes are derived from the isothermal magnetization curves measured at different temperatures. The magnetic-entropy change of the DyAl2 nanoparticles is lower than that of the bulk DyAl2 material but has a broadened peak. (c) 2005 Elsevier B.V. All rights reserved.

In order to investigate the behaviour of the magnetic anisotropy and the Mn–Mn exchange interaction in RMn 6 Sn 6 (R = rare earth) compounds, magnetic studies have been carried out on single crystals of RMn 6 Sn 6 compounds in which R is one of the non-magnetic elements Sc, Y and Lu. The temperature dependence of the magnetization of these compounds has been measured with the field applied parallel and perpendicular to the crystallographic c -direction. Magnetic isotherms of the three compounds were measured at 4.2 K in magnetic fields up to 50 T, applied parallel and perpendicular to the c -direction, sufficiently high to reach the forced ferromagnetic state and to detect multiple field-induced transitions. For LuMn 6 Sn 6 , magnetic isotherms were measured also at a higher temperature of 150 K. From our results we may conclude that the magnetic anisotropy as well as the antiferromagnetic coupling strength increases in the sequence of ScMn 6 Sn 6 , YMn 6 Sn 6 and LuMn 6 Sn 6 .

We have measured the temperature dependence of the magnetization on single crystals of the RMn 6 Sn 6 compounds with R = Gd, Tb, Dy and Ho. The observed magnetic-ordering temperatures and the anisotropy types agree well with earlier results from literature. Measurements of the magnetization with the field applied along the main crystallographic directions have been made at 4.2 K in magnetic fields up to 55 T. Field-induced transitions are observed that are interpreted in terms of the interplay between the antiferromagnetic intersublattice R–Mn coupling and the magnetocrystalline anisotropy.

Single crystals of TmMn 6 Sn 6− x Ga x compounds (0 ≤ x ≤ 1.22) obtained in a tin flux have been studied by thermomagnetic and high-field magnetization measurements. A collinear-antiferro to heli-magnetic transition at 324 K has been observed in TmMn 6 Sn 6 . Spin-reorientation transitions at low temperature are found in the compounds with x = 0.66 and 1.22. The magnetization curves in high fields at 4.2 K are interpreted to result from the competition between the Tm–Mn exchange interaction and the magnetocrystalline anisotropy of the Tm and Mn sublattices. A strong easy-plane anisotropy is favored for the Ga-poor compounds and a strong easy-axis anisotropy for the Ga-rich compounds while the compounds of intermediate Ga content (0.51 ≤ x ≤ 0.66) display rather weak magnetocrystalline anisotropy.

We present the (x, T) phase diagram of the ferromagnetic Y2Co17−xCrx (x = 1.17, 1.76, 2.34, 3) compounds with rhombohedral structure (space group R 3 ¯ m , Th2Zn17-type), determined for the entire magnetically ordered regime from high-resolution neutron-diffraction data. Substitution of small amounts of Cr for Co was found to have drastic effects on the magnetic properties such as a decrease of the Curie (TC) and spin reorientation (TSR) temperatures as well as a decrease of the ordered-moment values. These effects could be brought into connection to the fact that Cr was found to have a preference for the four Co sites in the following order 6c > 18f > 9d > 18h. The number of Cr atoms found occupying the latter two sites, however, is within experimental error negligible. The magnetic phase diagram comprises three distinct regions of magnetic order in addition to the paramagnetic state: (a) the HT range (easy axis), (b) the LT (easy plane) for 0

The hexagonal TmCuAl is studied with magnetic specific heat, resistivity and Tm 169 Mossbauer spectroscopy measurements. TmCuAl orders antiferromagnetically at T N = 1.9 K. The distance between the two levels of the quasi-doublet ground state of TmCuAl, determined with the Tm 169 Mossbauer pseudo-quadrupole shift, amounts to 2.8(3) K. Based on the temperature dependence of the Tm 169 quadrupole splitting a provisional calculation has been made for the crystal field diagram with a coupling constant α , which is non zero.

The Mossbauer spectra of Nd6Fe13Ag and Nd6Fe13AgH13 have been measured between 85 and 295 K and analyzed with a model that takes into account the basal magnetic anisotropy, the iron and hydrogen near-neighbor environments of the five crystallographically and magnetically inequivalent 4d, 16k, 16k′, 16l1, and 16l2 iron sites in the former and the six crystallographically and magnetically inequivalent 4d, 16k, 16k′, 16l1, 16l2−1 and 16l2−2 iron sites in the latter, where the additional site results from a predominance of hydrogen as near-neighbors on the iron 16l2 site. The increases in hyperfine field and isomer shift observed upon hydrogenation are in agreement with the increase in Wigner–Seitz cell volumes of each site and the changes in the near-neighbor environments.

We have studied the magnetic properties and magnetic-entropy changes of Mn1.1Fe0.9P0.7As0.3–xGex compounds with x = 0, 0.05, 0.1, 0.15 and 0.3. X-ray diffraction (XRD) study shows all the compounds crystallize in the Fe2P-type structure. Magnetic measurements show that the Curie temperature increases from 150 K for Mn1.1Fe0.9P0.7As0.3 to 380 K for Mn1.1Fe0.9P0.7Ge0.3. A field-induced first-order magnetic phase transition is observed above the Curie temperature for the compounds with x up to 0.15. There exists an optimal composition in which the first-order phase transition is the sharpest. The optimal composition for this system is x = 0.1. The maximal magnetic-entropy change derived from the magnetization data is about 40 J/(kg K) for a field change from 0 to 3 T.

The magnetic ordering of the hexagonal (P63/mmc) RCuSi (R=Dy, Ho) compounds has been studied by neutron powder diffraction. Magnetic ordering occurs below TN=11.9 K for R=Dy and 9.5 K for R=Ho and is associated with the wave vectors, q1=(0,0,q1z) and q2=(q2x,0,q2z) for both compounds. At 1.5 K the length of the wave vector q1 is close to the commensurate value q1z≈1/6 for both compounds and that of q2≈(1/15,0,1/6) for DyCuSi and q2≈(1/13,0,1/7) for HoCuSi. The wave vector length displays more important changes with temperature for the R=Dy compound than for R=Ho. Various models are discussed. For amplitude modulated arrangements of the R moments the amplitude of the waves (Fourier coefficients) are for the q1 structures 3.1(1)μB/Dy and 3.9(1)μB/Ho and for the q2 structures 5.9(2)μB/Dy and 7.8(1)μB/Ho. The two structures coexist in form of domains. The present investigation is based on simultaneous refinements of high-resolution and high-flux data. Our results differ in several points from recently published data.

The structural and magnetic properties of Sm2Co17-xCrx (0 less than or equal to x less than or equal to 3.0) compounds have been investigated by means of X-ray diffraction and magnetization measurements. The powder X-ray diffraction patterns show that all samples crystallize as a single phase with the rhombohedral Th2Zn17-type structure. The lattice parameters a and V increase monotonically with increasing Cr content, but the lattice parameter c increases very slowly with increasing Cr content. The X-ray diffraction patterns of the aligned powder of the samples have confirmed that all the compounds investigated have uniaxial anisotropy. The Curie temperature of the compounds decreases rapidly the spontaneous magnetization M-0, the anisotropy field B-a, and the anisotropy constant K-1 of Sm2Co17-xCrx (0 less than or equal to x less than or equal to 3.0) compounds decrease strongly with increasing Cr content. (C) 2004 Elsevier B.V. All rights reserved.

The effect of nanoscale exchange coupling has been investigated in the CoPt alloy system. The experimental results of XRD and TEM indicate that in the early stage of the disorder-order transformation, the ordered fct regions with a mean size smaller than 8 nm are uniformly distributed and randomly oriented along the a-, b- and c-axes of the cubic structure of the original disordered fcc matrix phase. Both phases are completely coherent. The degree of atomic order in the ordered regions continuously increases, but this process is different for the various ordered regions. Also the degree of atomic order of the matrix phase increases, albeit at a low rate. There is a broad continuous distribution of the degree of order in the initial stage of the ordering transformation. An ordered region with higher degree of order has a higher magnetocrystalline anisotropy. The effect of nanocomposite exchange coupling between the regions with different degree of order is very clear. A remanence ratio of 0.78 is obtained after annealing the sample at 675 degreesC for 20 min. When the annealing time is longer than 60 min at 675 degreesC, the growth of ordered regions leads to a situation in which the disordered regions are swallowed up and the ordered regions meet each other to form antiphase boundaries. Cross-intersected polytwin bands of several hundreds nm length and a few nm width are formed along the {111} and {211} planes to relax the strain energy. It is suggested that the mechanism of magnetization reversal changes from coherent rotation to magnetic-domain wall movement. Since the widths of the polytwin bands are still within the length of exchange coupling, the strong remanence enhancement is preserved. (C) 2003 Elsevier B.V. All rights reserved.

The alloy MnFeP 0.45 As 0.55 has been identified as a promising material to be used as magnetic refrigerant for room-temperature applications. This alloy, which is derived from the well-known iron pnictide Fe 2 P, exhibits a first-order temperature- and field-induced magnetic phase-transition. The Curie temperature can be varied by substitutions into the pnictide sublattice. We studied the effect of Ge substitution in this material. Most strikingly, we find a strong increase of the magnetic ordering temperature up to 570 K and a concomitant increase of the ordered magnetic moment up to 4.25 μ B /f.u. for the alloy MnFeP 0.5 Ge 0.5 . On substitution with the large Ge ions, the expected lattice expansion is very anisotropic. We observe an increase and decrease of the a and c parameter of the hexagonal lattice, respectively. Compared with the (P,As) series, for a similar volume change we find a much stronger increase of T C . This confirms the importance of competing exchange interactions in this interesting alloy system.

We have used neutron diffraction and magnetic measurements to investigate the changes in magnetic properties of the Kondo semimetal compound CeNiSn after charging with deuterium gas under moderate conditions. Charging with deuterium led to the formation of the monodeuteride CeNiSnD with filled TiNiSi structure. This compound gives rise to long-range antiferromagnetic ordering below T N =5.1 K. The ordered magnetic moment value equals 1.37(3) μ B per Ce atom, the moments pointing along the [001] direction. No significant ordered magnetic moment on the Ni atoms has been observed by powder neutron diffraction.

Neutron diffraction performed on deuterated powder samples of Pr 6 Fe 13 Au shows that the crystal structure of the parent compound is retained upon charging with deuterium. The refined composition of the deuteride is Pr 6 Fe 13 AuD 13 . The deuterium atoms occupy various types of interstitial sites bounded by Pr and Fe atoms. Each of these sites is surrounded by at least two Pr atoms. A collinear antiferromagnetic ordering of the four Fe and the two Pr sublattices was reported previously for the uncharged Pr 6 Fe 13 Au compound. By contrast, a collinear ferromagnetic structure has been derived from the present neutron data of the deuteride. The easy moment direction is the same in Pr 6 Fe 13 AuD 13 and Pr 6 Fe 13 Au, being perpendicular to the c-axis. For the deuteride this result was derived from a complementary synchrotron radiation X-ray study made on magnetically aligned particles of the ferromagnetic deuteride.

We synthesized for the first time the intermetallic compound Fe2MnGe. To avoid preferential evaporation of volatile components we exploited mechanical alloying. Amorphous Fe2MnGe alloy powder was prepared by planetary ball milling elemental starting materials. The amorphous-to-crystalline transition was studied by means of differential scanning calorimetry (DSC) and X-ray diffraction (XRD). A cubic D03 phase is formed at low temperature and transforms to a high-temperature hexagonal D019 phase. The apparent activation energy was determined by means of the Kissinger method.

The magnetic phase transitions and the magnetocaloric properties of the pseudo binary system Mn 5− x Fe x Si 3 with x =0, 1, 2, 3, 4, 5 have been investigated by measuring the magnetisation as a function of temperature and magnetic field. With increasing Fe content, the antiferromagnetic ordering temperature shifts to higher temperatures. The compound Mn 5 Si 3 is an antiferromagnet with a field-induced transition. At 4.2 K, the Mn 5− x Fe x Si 3 compounds with x =1 and 2 display antiferromagnetic behavior up to 38 T. For the compounds with x =4 and 5 we find ferromagnetic order. The magnetic-entropy changes in this system are derived from the temperature and field dependence of the magnetization by means of the thermodynamic Maxwell relation. For the MnFe 4 Si 3 compound, enhanced but modest magnetic-entropy changes are observed.

The effect of the atomic disorder–order transformation on remanence enhancement and coercivity in isotropic CoPt magnets has been studied by isothermal annealing at 675°C, well below the transformation temperature, for 10–80 min after quenching in ice–water from 900°C. The results of X-ray diffraction, transmission electron microscopy, alternating-current (ac) susceptibility and magnetization measurements indicate that the strong remanence enhancement effect originates from exchange coupling between the face-centered-tetragonal (fct) ordered hard-magnetic precipitated phase and the face-centered-cubic (fcc) disordered soft-magnetic matrix phase during the initial ordering transformation. The non-uniform distribution of the magnetic anisotropy results in a lower reversibility, unlike the so-called exchange spring magnet.

In GdNi5, the muon localizes at the 3f interstitial site and below ∼80 K a second muon site becomes populated, either at the 6m or 6k site. These latter sites are located in a ring surrounding the (0, 0, 1 2 ) site and the muon occupies all six sites within the time range of the experiment (10−9 s). This ring site is metastable and the muon hops to the preferred 3f site. We determine the mean time of stay of the muon in the ring site and show that it is governed by a multi-phonon quantum diffusion process. The coincidence energy is measured to be Ea=272 (10) K and the tunneling matrix element J=0.11 (2) meV.

We have studied the magnetic properties of an Y2Co15Si2 single crystal. The magnetic anisotropy has been analyzed in the temperature range 5-350 K by means of the Sucksmith-Thompson method. Both the first-order anisotropy constant K-1 and the second-order anisotropy constant K-2 are found to be positive, the former being more than an order of magnitude larger than the latter at all temperatures. Measurements of the field dependence of the magnetization made in the easy and hard direction show that there is small but significant anisotropy of the saturation moment. (C) 2002 Elsevier Science B.V. All rights reserved.

We have studied the occurrence of spin–reorientation transitions in the tetragonal La 2− x Ho x Co 14 B compounds in the concentration range 0.2≤ x ≤1.8. Spin orientations in these compounds arise from the competition between the Ho-sublattice anisotropy and the Co sublattice anisotropy. The former dominates at low temperatures, favouring an easy-cone direction of the magnetization at the lowest temperatures followed by an easy magnetization direction parallel to the c -axis at intermediate temperatures. The Co-sublattice anisotropy dominates at high temperatures and favours an easy direction perpendicular to the c -axis. A magnetic phase diagram is presented.

We have studied DyFe4Ge2 and ErFe4Ge2 with 57Fe, 161Dy and 166Er Mossbauer spectroscopy. DyFe4Ge2 has a c axis anisotropy, whereas ErFe4Ge2 could be interpreted with two subspectra with both an angle with respect to the c axis. In ErFe4Ge2 a magnetic phase transition is observed at T=8 K.

We have studied the magnetic properties of a single crystal of the DyCo 10 V 2 compound. This compound has the tetragonal ThMn 12 structure. The easy magnetization direction is parallel to the c axis at high temperatures. The magnetization tilts away from the c axis below the spin reorientation temperature at T SR =42 K, reaching a value of θ C =27° at 5 K. The magnetic compensation of the Co and Dy sublattice magnetizations leads to a sharp minimum at T COMP =118 K. The shape of the M ( T ) curves is strongly field-dependent and is considerably influenced by the thermal history of the sample. This behaviour is attributed to the development of a rather strong intrinsic coercivity at low temperatures, originating from the presence of narrow Bloch walls. The temperature dependence of the coercivity, diverging at the compensation temperature, was compared with model predictions.

We have studied the concentration dependence of the anisotropy constants and spontaneous moments of several compounds of the series Gd 2 Co 17− x Ga x and Gd 2 Co 17− x Al x . We have used these data in a simple model based on the mean-field approach and crystal-field theory to explain why spin reorientation transitions observed in the temperature dependence of the magnetization of several R 2 Co 17− x Al x compounds do not occur in the corresponding R 2 Co 17− x Ga x compounds.

Specific-heat measurements have been performed on the tetragonal ThMn 12 -type RCr 4 Al 8 compounds with R=La, Ce, Pr, Gd and Er in the temperature range 1.5–200 K. For ErCr 4 Al 8 the measurements were extended down to 0.5 K and were also carried out in an applied field of 12 T. Anomalies associated with the magnetic ordering of the R sublattice were observed in the low-temperature part of the specific-heat curves for the compounds with R=Gd and Er below about 6 and at 0.5 K, respectively. No magnetic ordering was found in PrCr 4 Al 8 and CeCr 4 Al 8 .

The effect on the magnetocrystalline anisotropy of substitution of several types of non-magnetic atoms into the various Co sites of R 2 Co 17 compounds has been studied. A substitution scheme is presented taking into account size effects as well as enthalpy effects. The effects of preferential substitution into the various Co sites have been correlated with changes in anisotropy derived from magnetic measurements. Particular attention has been given to various types of spin-reorientation transitions occurring in the temperature dependence of the magnetization.

We have studied the magnetic properties of several series of RFe 11− x Co x Ti compounds (R=Tb, Er and Y) by means of magnetic measurements and X-ray diffraction of magnetically aligned powder samples. The spin reorientations observed in several of these compounds were attributed to three different mechanisms. Spin-reorientation transitions observed at fairly low temperatures originate mainly from a competition between the various crystal-field terms associated with the crystal-field-induced R-sublattice anisotropy. At fairly high temperatures, spin reorientation transitions can arise as a consequence of a sign change of the 3d-sublattice anisotropy as a function of temperature. In the intermediate temperature range, spin-reorientation transitions were interpreted as resulting from a competition between the R-sublattice anisotropy and 3d-sublattice anisotropy.

We have studied the magnetic properties of GdT 4 Al 8 and GdT 6 Al 6 compounds with T=Cr, Mn, Cu by means of standard magnetization and susceptibility measurements, magnetization measurements in high fields up to 35 T, and measurements of the specific heat. In these GdT 4 Al 8 compounds, the T element does not carry a magnetic moment. In all these cases, the coupling between the Gd moments is fairly weak and leads to antiferromagnetic ordering at rather low temperatures. We have analyzed our data in terms of a simple mean-field two-sublattice model. Reliable values of the intersublattice coupling strength were derived from high-field measurements made on free powder particles. In the GdT 6 Al 6 compounds, more than one crystallographic site is occupied by the T elements, leading to relatively strong changes in the magnetic ordering temperatures. A comparison is made with the magnetic properties of GdFe 4 Al 8 and GdFe 6 Al 6 compounds in which the Fe moments strongly determine the magnetic properties. High-field measurements are presented also for the latter two compounds.

The magnetic ordering of the orthorhombic CeNi0.78Sn2 and Ce3Ni2Sn7 compounds has been studied by neutron diffraction. Ce3Ni2Sn7 has two Ce sites of distinct symmetry. Only the Ce2 moments with a trigonal prism arrangement were found to order below TN=3.8 K with a collinear antiferromagnetic moment arrangement along the a-axis associated with the wave vector q=(0,1,0). At 1.5 K the ordered moment value is 1.9(1)μB/Ce atom. The compound CeNi0.78Sn2 with a single Ce site but with a similar trigonal prism arrangement as Ce3Ni2Sn7 was found to order at 1.5 K with two coexisting magnetic phases in equal amounts. One of these is ferromagnetic TC=2.3 K while the other phase is a transversal sine wave modulated phase with q2=(0qy0) ordering at TN=4.0 K. The ordered magnetic moment value/amplitude at 1.5 K in both phases is 2.0μB/Ce atom and points to the same direction along c. The observation of two magnetic phases so far observed in several off stoichiometric phases of the CeNixSn2system is attributed to the concentration fluctuations associated with the Ni deficiency.

We have studied the magnetic properties of the GdT 2 Ge 2 compounds (T=3d: Fe, Co, Ni, Cu, 4d: Ru, Rh, Pd) by means of DC susceptibility and high-field free-powder (HFFP) measurements. All compounds investigated were found to order antiferromagnetically at low temperatures. The two-sublattice model, without anisotropy, has been used to obtain experimental values for the intrasublattice coupling constant n 11 , and the intersublattice exchange coupling constant n 12 . The values of the intersublattice constants derived from the high-field data are in good agreement with those obtained from the temperature dependence of the susceptibility. The variations of n 11 and n 12 across the 3d and 4d series in GdT 2 Ge 2 have been discussed in terms of changes of the lattice parameters, the unit-cell volume V and modifications of the transition metal electron band.

The structure and magnetic properties of Pr 2 Co 17− x Si x compounds with Si concentrations up to x =2 were studied by means of X-ray diffraction and magnetic measurements. All compounds have the rhombohedral Th 2 Zn 17 -type structure. At room temperature, the easy magnetization direction is perpendicular to the c -axis in all compounds. Above room temperature, a spin-reorientation transition takes place in Pr 2 Co 17− x Si x compounds with x =1.5 and 2. The Co moment and the Curie temperature decrease strongly with increasing Si concentration. The rotation-alignment method was employed to magnetically align fine powder particles of Pr 2 Co 17− x Si x compounds along their c -axis. The field dependence of the magnetization was measured on the rotation-aligned samples with the field applied along the rotation ( c ) axis, from which the anisotropy constant K 1 was derived by means of the Sucksmith–Thompson method. The absolute value of K 1 and the anisotropy field H A decrease monotonically with increasing Si concentration.

The magnetic behaviour of the TbMn 6− x Cr x Sn 6 ( x =1, 2) compounds has been studied by neutron diffraction and magnetic measurements. Both compounds exhibit a uniaxial ferromagnetic moment arrangement for both magnetic (R and Mn) sublattices, which order simultaneously and are coupled antiferromagnetically over the entire ordered regime below T C . A spin reorientation transition occurs at lower temperatures ( T t ). The magnetic phase diagram comprises three regions. In the high temperature range T t – T C the magnetic moments are confined to the basal plane. In the intermediate region T t – T i spanning about 40–50 K the moments rotate smoothly by 90 K. In the low temperature range 1.5 K– T i the magnetic moments of both sublattices point into the c -direction. The ordered moment values at 1.5 K are 8.62(5) μ B and 8.9(1) μ B per Tb atom and 2.09(2) μ B and 1.88(3) μ B per (Mn/Cr) atom for the two compounds TbMn 5 CrSn 6 and TbMn 4 Cr 2 Sn 6 , respectively. Alloying with the almost non-magnetic Cr leads to a linear decrease of the ordering and of the spin reorientation temperatures.

The evolution of the magnetic anisotropy of (Ce,Y)2Co17 compounds with increasing Ce concentration was investigated by magnetic measurements and X-ray diffraction on magnetically aligned powders. At room temperature the easy magnetization direction changes from perpendicular to the c-axis to parallel to the c-axis with increasing Ce concentration. A spin-reorientation transition from easy-axis anisotropy at higher temperatures to easy-plane anisotropy at lower temperatures arises at about 600, 530 and 320 K in Ce1.3Y0.7Co17, Ce1.5Y0.5Co17 and Ce1.7Y0.3Co17, respectively. The Curie temperature and spontaneous magnetization decrease with increasing Ce concentration. These magnetic behaviours are discussed in terms of the itinerant 4f states of Ce ion and the hybridization between the cobalt 3d states and the cerium 4f states.

Specific-heat measurements have been performed on the tetragonal ThMn 12 -type RFe 4 Al 8 compounds with R=Pr, Dy and Tm in the temperature range 1.5 to 200 K. The compound PrFe 4 Al 8 gives rise to a λ-type anomaly at 11.3 K. In DyFe 4 Al 8 we found anomalies at 8.6 K and at about 30 K, while in TmFe 4 Al 8 there is an anomaly below 1.5 K. From the temperature dependence of the magnetic entropy in the presently studied compounds and from data obtained in earlier investigations, it is concluded that the overall crystal-field splitting in the RFe 4 Al 8 compounds with R=Pr, Nd, Dy, Ho, Er and Tm is less than 200 K.

Specific-heat measurements have been performed on the tetragonal ThMn 12 -type RMn 4 Al 8 compounds with R=Y, La, Pr, Nd, Dy and Er in the temperature range 1.5 to 200 K. The compound PrMn 4 Al 8 gives rise to a λ-type anomaly at 14 K. No anomalies indicative of magnetic ordering were found above 1.5 K in the specific-heat curves of the RMn 4 Al 8 compounds with R=Y, La, Nd, Dy, and Er. From the temperature dependence of the magnetic entropy, it is concluded that the overall crystal-field splitting in the compounds with R=Pr, Nd, Dy, and Er is of the order of 200 K or even less.

We have studied the magnetic properties and magnetic-entropy changes of the MnFeP0.5Ge0.5−xSix compounds with x = 0.1, 0.2, 0.3, 0.4 and 0.45. X-ray diffraction shows that the compounds crystallize in the Fe2P-type hexagonal structure. The lattice parameter a and the Curie temperature decreases with increasing x. The maximal magnetic-entropy changes for x = 0.4 and 0.45 derived from the magnetization data are about 6.0 J/kg K and 5.8 J/kg K, respectively, for a field change from 0 to 1.5 T.

Nanocrystalline exchange coupled Sm2Fe14.5+nCu0.5Ga2C2 magnets with enhanced remanence were produced using melt spinning. Starting from nearly single phase Sm2Fe14.5Cu0.5Ga2C2 alloys, the content of additional α-Fe in the composite magnets was stepwise increased up to more than 50 wt.%. A maximum remanence ratio of Mr/Ms=0.65 was found in samples containing 8.3 wt.% α-Fe, whereas the coercive field was μ0Hc=1.6 T for this composition. Magnetic-force microscopy investigations for samples with n=0 and 4 reveal that the magnetic-domain-length scale is within the range 800–1500 nm. This is larger than the grain size, indicating the existence of exchange coupling between the hard and soft phase.

The crystal structure and magnetic ordering of HoFe 6 Ge 6 annealed at 800°C are studied by neutron powder diffraction. The crystal structure consists of the host (Fe, Ge) and guest (Ho/Ho* and Ge/Ge*) subsystems. In view of the complex magnetic ordering the guest subsystem was preferably described as using two types of microdomain with a 1:3 volume ratio. In the first type of microdomain (I) the guest subsystem is fully disordered (average YCo 6 Ge 6 structure); in the second type (II) it is fully ordered (TbFe 6 Sn 6 superstructure, wave vector q =(1/2 1/2 0) of the orthohexagonal average structure). The limited coherence of microdomains leads to an anisotropic broadening of the satellites and can be described within a needle-like model (infinite ‖ [100] and small ⊥ [100]) with a mean correlation length 84(6) A. The Fe-moments order antiferromagnetically below T N ≈450 K with the wave vector q 1 =(1 0 0) in the superstructure basis for both types of microdomain. The Fe-moments point along a and are arranged into ferromagnetic (1 0 0) layers stacked (+ - + -⋯) along the a -axis. The 1.5 K Fe ordered moment value is 1.80(7) μ B /Fe. The Ho-moments order antiferromagnetically below 9 K with two wave vectors q 1 =(1 0 0) and q 2 =(1/3 0 0) in the superstructure basis. The q 1 wave vector is associated with microdomain I and gives rise to a collinear arrangement of the Ho moments along a . The q 2 wave vector corresponds to microdomain II and leads to a modulated arrangement of the Ho moments within the (0 yz ) plane. The 1.5 K ordered moment values are 6.0(8) μ B /Ho (I) and 2.0(4) μ B /Ho (II). The antiferromagnetic Ho–Ho correlations have limited spatial extent with the mean correlation length 95(30) A (I) and 70(30) A (II).

The magnetic structure of the TbNixGe2 (x=0.8, 0.6) compounds has been studied by neutron powder diffraction. The paramagnetic neutron data confirmed the CeNiSi2 type of structure reported earlier for this compound. The magnetic ordering is associated with the wave vector q1=0 over the entire magnetically ordered regime for both compounds. The Tb moments adopt a uniaxial antiferromagnetic arrangement (Gz mode) with c as the preferred axis, invariant under the magnetic space group C 2 m′ 2′ c 2 1 ′ m similar to the x=0.4 and 1.0 compounds. At 1.5 K the refined moment values are: μTb=8.7(1)μB for x=0.8 and 8.9(1)μB for x=0.6. The (T,x) magnetic phase diagram indicates that TN increases linearly with increasing Ni content (31–42 K) in the 0.6

The magnetic structure of the compound HoFe2Ge2 (I4/mmm S.G) has been studied by neutron diffraction, magnetic and specific-heat measurements. The paramagnetic neutron data confirmed the ThCr2Si2 type of structure reported earlier for this compound. The analysis of the data collected in the magnetically ordered regime (TN=17 K) showed a uniaxial arrangement of the Ho moments along c associated with the wave vector q=(1/2,1/2,0). The moments of the atoms related by the non-primitive translation (1/2,1/2,1/2) are antiparallel. The refined moment value at 1.5 K is μHo=6.6(1) μB. In addition to the ordered phase the neutron data comprise diffuse magnetic peaks in the low-angle region demonstrating the coexistence of short-range order effects below 6 K.

The structural and magnetic properties of Ce2Co17−xAlx samples for Al concentrations up to x=5 were studied by means of X-ray diffraction and magnetic measurements. The 2:17 phase was found to exist only up to x=3.5. The easy magnetisation direction is parallel to the c-axis in all of the latter compounds. The Co moments and the Curie temperatures decrease strongly with increasing Si concentration. From magnetic measurements made on magnetically aligned powders, we have determined the concentration dependence of the anisotropy constant K1. The values of K1 increase with increasing x. This behaviour is discussed in terms of preferential Al substitution.

Neutron diffraction performed on Pr 6 Fe 13 Ag and Pr 6 Fe 13 Au powder samples reveals a collinear antiferromagnetic ordering of the four Fe and the two Pr sublattices associated with the wave vector q =(001) ( I P magnetic lattice with anticentering translation). The moments of all sublattices located at ( xy 0) layers, sandwiched between successive X layers perpendicular to z at z =−0.25, 0.25, are confined to the same direction within the ( xy 0) plane. They change their direction collectively when going to the next Ag(Au) layers at z =0.25, 0.75. The Pr moments at 1.5 K are 2.5(2)μ B and 2.6(1)μ B /Pr atom, while the average Fe ordered value is 2.2μ B /Fe atom, in agreement with Mossbauer results. Detailed results are presented for Pr 6 Fe 13 Ag.

Inelastic neutron scattering (INS) has been used to study the exchange interaction in polycrystalline samples of GdMn2Si2, GdMn2Ge2, GdMn6Sn6 and Gd6Mn23. Direct values of the molecular fields experienced by the Gd moments were obtained from the position of the dominant transition at low momentum transfer in the INS spectra. By using a simple spin wave model, also values of the Gd–Mn exchange constants in these compounds were derived. Our results are compared with results from different magnetic measurements.

We have studied the magnetic properties of several R 2 Co 17− x Ga x compounds with R=Y, Tb, Dy and Ho. X-ray diffraction measurements made on magnetically aligned powders of Y 2 Co 17− x Ga x compounds showed that these materials retain their easy-plane magnetisation at room temperature up to at least x =5. The difference in behaviour with the corresponding Gd compounds and the absence of spin-reorientation phenomena in R 2 Co 17− x Ga x compounds in which the R component has a negative second-order Stevens factor is discussed in terms of preferred site occupation of the Ga atoms. High-field measurements at 5 K were made on free powders of several Tb, Dy and Ho compounds. The intrasublattice constants derived from these data are somewhat smaller than those of the undiluted R 2 Co 17 compounds, which is also discussed in terms of preferred Ga site occupation.

In this report the possibilities to obtain experimental information on various physical properties of rare earth intermetallics by means of 155 Gd Mossbauer spectroscopy are reviewed. Results are discussed of compounds related to permanent magnet materials, hydrogen absorbing materials, superconducting and heavy-electron systems. Particular attention is paid to the electric field gradient V ZZ and its relation to the second order crystal field parameter A 2 0 . Experimental data are compared with results of electronic structure calculations.

The magnetic properties of Tb2Co17−xGax compounds (x=1,3,5 and 7) were studied by means of neutron diffraction and magnetic measurements. The refinement results of the neutron powder diffraction patterns show that initially the Ga atoms occupy almost exclusively the 18h site in the rhombohedral Th2Zn17 structure and presumably are responsible for the sign reversal of the Co sublattice anisotropy. For x≥3 the Ga atoms increasingly occupy the 6c and 18f sites at the cost of the 18h site that shows a decreasing Ga occupancy in this concentration range. The 9d site is completely avoided by the Ga atoms over the whole concentration range. The sign reversal of the Co sublattice anisotropy is attributed to filling of the 18h site with Ga. From magnetic measurements and neutron diffraction it is derived that the Co moment strongly decreases in size with Ga concentration. There is also a strong decrease of the Curie temperature with Ga concentration.

The crystallographic and magnetic properties of the Ce2Ni15Si2 compound was studied by means of neutron diffraction at room temperature and at 2 K. The refinement results of the neutron powder diffraction pattern show that this compound crystallises in the rhombohedral Th2Zn17-type structure. There is a distinct preference for the Si atoms to occupy the 9d site. No magnetic ordering was detected either at room temperature or at 2 K in the neutron diagram. From XAFS experiments it was derived that Ce is in an intermediate valence state in this compound.

We have studied the magnetic properties of Ho2Co17-xGax compounds (x less than or equal to 7) by means of magnetic measurements and X-ray diffraction on magnetically aligned powders. The Curie temperature and the spontaneous moment decrease strongly with increasing Ga concentration. The compounds that are magnetically ordered at roam temperature have an easy magnetisation direction at room temperature which is perpendicular to the c-direction. (C) 1998 Elsevier Science S.A.

The specific heat of a CeCoAl 4 single crystal has been studied in magnetic fields up to 17.5 T. In zero field, this compound has been found to order antiferromagnetically below the Neel temperature of about 13.5 K. The effect of the magnetic field is different when it is applied along the different crystallographic axes. Along the a -axis, with increasing magnetic field, the Neel temperature slightly decreases and reaches a value of 12.7 K at 17.5 T. Along the b -axis, the Neel temperature decreases more strongly with increasing magnetic field. At 16 T, we found a value of T N of about 6.9 K. At 17.5 T, along the b -axis, we observed a rather broad peak in the specific heat which is associated with a transition from paramagnetism to ferromagnetic order. Along the c -axis, a drastic change in the specific heat occurs at a field between 7–8 T. At 7 T, the value of T N is about 9 K. At fields higher than 8 T, the specific heat is evidently characterised by a transition from paramagnetism to ferromagnetic order. The critical values of the magnetic field above which ferromagnetic order is formed at low temperature turn out to be consistent with the measurements of the magnetisation curves at 4.2 K.