Showing papers on "Antiferromagnetism published in 1986"

Magnetic properties of superlattices formed from ferromagnetic and antiferromagnetic materials.

Abstract: We present theoretical studies of basic magnetic response characteristics of superlattice structures formed from alternating layers of ferromagnetic and antiferromagnetic materials, each described through use of a localized spin model. The geometry explored here is one in which the antiferromagnet consists of sheets parallel to each interface within which the spins are aligned ferromagnetically. The study of the classical (mean-field) ground state as a function of magnetic field shows that a sequence of spin-reorientation transitions occur, particularly for superlattices within which the antiferromagnetic constituent consists of an even number of layers. For the various phases, we present calculations of the spin-wave spectrum, and also the infrared absorption spectrum.

Lattice model of microemulsions

Abstract: A lattice model of microemulsions is proposed. It proves to be equivalent to a spin‐1/2 Ising model in a magnetic field, with ferromagnetic nearest‐neighbor, antiferromagnetic next‐nearest‐neighbor (next‐nearest defined as two lattice steps, regardless of the metrical distance), and three‐spin interactions. The respective interaction constants H, J, M, and L in the Ising model are related to the ratios zBB/zAA and zAB/(zAAzBB)1/2 of the activities of the oil (AA), water (BB), and surfactant (AB), to the surfactant‐film‐curvature energy (surfactant–surfactant interaction energy) K, and to the curvature‐bias parameter (Bancroft parameter) λ, in the microemulsion model. A table of translations is given. In mean‐field approximation the symmetrical version of the model, in which H=L=0 (or zBB/zAA =1 and λ=0 in microemulsion language), is equivalent also to the ANNNI (anisotropic, or axial, next‐nearest‐neighbor Ising) model. The analog of the three‐phase (Winsor III) equilibrium of surfactant solutions is iden...

Ferromagnetism versus aniferromagnetism in face-centered-cubic iron.

Abstract: Using a first-principles disordered-local-moment picture of itinerant-electron magnetism, we calculated the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state.

Wave-vector- and magnetic-field-dependent spin fluctuations in the heavy-fermion system CeCu6.

Abstract: We have performed neutron-scattering measurements on a single crystal of ${\mathrm{CeCu}}_{6}$ in applied magnetic fields from 0 to 6.4 T. The observed momentum-dependent magnetic scattering implies the existence of short-range antiferromagnetic correlations. While it induces no resonances, the field broadens the spectra considerably at T=0.4 K. An effective Hamiltonian which incorporates both single-impurity Kondo properties and antiferromagnetic Ruderman-Kittel-Kasuya-Yosida interactions describes our data.

Magnetic behavior of nonet tetracarbene as a model for one-dimensional organic ferromagnets.

Abstract: Tetracarbene (1) was generated by photolysis of the corresponding tetradiazo compound (2) in a 2-methyltetrahydrofuran glass or a single crystal of benzophenone at cryogenic tempreatures. The temperature dependence of paramagnetic susceptibility revealed its nonet spin multiplicity in the ground state. A behavior suggesting the presence of antiferromagnetic intermolecular interaction was also found when generated in the glass. The field dependence of magnetization of 1 was analyzed in terms of the Brillouin function and the experimental data fit closely to that of the theoretical value for J = */*. This is independent evidence for the nonet spin multiplicity of 1. The characteristic saturation behavior of magnetization in 1 was found to be due to its high spin multiplicity. Thus 1 may be regarded as a molecular superparamagnet. In the polycarbenes, the localized n spins a t carbenic centers are aligned all in parallel through the electron correlation between the mobile K spins, resulting in the intramolecular ferromagnetic spin ordering. Although the mechanism of spin ordering of a spins in polycarbenes is entirely different from that in metallic ferromagnets, the interaction between n and K spins resembles s-d interaction in dilute alloys. The potentiality of polycarbenes as a microdomain in macroscopic ferromagnets will be discussed. The explosive growth in the number of reports on organic conductors and superconductors has arisen from genunie interests in mobility of electrons in organic molecular crystals, components of which are insulators in themse1ves.I On the other hand, molecular design of organic ferromagnets which is becomming the current topic of theoretical interest in organic material science deals with the behavior of electron spins in organic molecules.* One of the strategies toward this goal is to construct organic molecules with high-spin multiplicity as domains in ferromagnets and to introduce ferromagnetic intermolecular (interdomain) interaction among them. High-spin organic molecules are accessible when nonbonding molecular orbitals are present due to the symmetry of the alternant hydrocarbon skeleton. Examples of the above category are m-phenylenebi~(phenylmethylene),~ its higher homologues, 3,6-dimethyleneanthracenediyl1,8-dioxyI$ etc. Recently we have generated tetracarbene, m-phenylenebis((diphenylmethylen-3-y1)methylene) (1) and proved its nonet spin multiplicity in the ground state by analyzing ESR fine structures of the sample oriented in a host single crystal of ben~ophenone.~ Now we have studied the magnetic behavior of this highly important tetracarbene 1 by means of magnetic susceptibility measurements.6 The magnet was composed of a main coil and a pair of reverse Helmholtz coils for the field gradient. The main field gradient, the temperature of a sample, and the weight change were carefully calibrated to enable the absolute magnetic susceptibility measurement. Inhomogeneity of the main magnetic field (HM) was leis than 0.2 T/m at the center of the main coil with the accuracy of lo-’. The accuracy of the field gradient (aHG/az) is better than IO-’ which was calibrated by a GaAs Hall device. The temperature of the cryostat (300-20 K) was regulated by the microcomputer, and data were recorded when the temperature stabilized within O.l%/min. The temperatures between 20 and 4 K were controlled manually by adjusting the flow of liquid helium, and lower temperatures than 4 K were obtained by pumping liquid helium. A platinum-resistance thermometer was used to read temperatures higher than 25 K and a carbon-resistance thermometer for lower temperatures. These temperature readings were calibrated in the whole temperature range with a magnetic thermometer with use of paramagnetic Cr(NH3)I Sculz, H. Adu. Phys. 1982, 31, 299. (b) Torrance, J . B. Arc. Chem. Res. 1979, 12, 79. (2) (a) McConnell, H. M. J . Chem. Phys. 1%3,39, 1910. (b) McConnell, H. M. Proc. Robert A . Welch Found. ConJ Chem. Res. 1967,1I, 144. (c ) Mataga, N. Theor. Chim. Acra 1968,10,372. (d) Ovchinnikov, A. A. Dokl. Akad. Nauk SSSR 1977, 236, 928. (e) Ovchinnikov, A. A. Theor. Chim. Acra 1978,47,297. (f) Buchachenko, A. L. Dokl. Akad. Nauk SSSR 1979, 244, 1146. (8) Breslow, R.; Juan, B.; Kluttz, R. Q.; Xia, C. 2. Terrahedron 1982,38,863. (h) Iwamura, H.; Sugawara, T.; Itoh, K.; Takui, T. Mol. Crysr. Liquid Cryst. 1985, 125, 251. (i) Breslow, R. Ibid. 1985, 125, 261. Q) Ooster, S.; Torrance, J. B.; Scumaker, R. R. The 1984 International Chemical Congress of Pacific Basin Societies, Abstract of Papers 07E28, Honolulu, Hawaii, December 1984. (3) (a) Itoh, K. Chem. Phys. Left. 1967,1, 235. (b) Itoh, K. Pure Appl. Chem. 1978, 50, 1251. (c) Wasserman, E.; Murray, R. W.; Yager, W. A.; Trozzolo, A. M.; Smolinsky, G. J. J . Am. Chem. SOC. 1967, 89, 5076. (4) (a) Seeger, D. E.; Berson, J . A. J . Am. Chem. SOC. 1983, 105, 5144. (b) Seeger, D. E.; Berson, J. A. Ibid. 1983, 105, 5146. (5 ) (a) Teki, Y.; Takui, T.; Itoh, K.; Iwamura, H.; Kobayashi, K. J . Am. Chem. SOC. 1983, 105, 3722. (b) Teki, Y . ; Takui, T.; Itoh, K.; Iwamura, H.; Kobayashi, K., to be published. ( 6 ) (a) Sugawara, T.; Bandow, S.; Kimura, K.; Iwamura, H.; Itoh, K. J . Am. Chem. SOC. 1984, 106, 6449. (b) Kimura, K.; Bandow, S. Solid State Phys. 1984, 20, 467. 0002-7863/86/ 15O8-0368$01.50/0

Systematics across the UTX series (T = Ru, Co, Ni; X = Al,Ga, Sn) of high-field and low-temperature properties of non-ferromagnetic compounds

Abstract: Results are presented of magnetic and specific-heat studies performed on some equiatomic compounds of the series U TX with a special emphasis on non-ferromagnetic UNiAl, UCoAl, URuA1 and URuGa. The occurrence of magnetism in these compounds is attributed mainly to the 5f electrons of uranium. The systematics of the ground-state properties across the series is discussed with respect to delocalization mechanisms of the 5f electrons. The possible role of spin fluctuations in the low-temperature behaviour of UCoAl, URuAl and URuGa is indicated by magnetic measurements. The compound with the highest γ value, UNiAl (γ = 167 mJ/mol K 2 ), behaves as an itinerant antiferromagnet.

Magnetic Properties of Layered Compound MnPS3

Abstract: Magnetic properties of a layered compound MnPS 3 were investigated by means of magnetic susceptibility, high field magnetization and electron spin resonance. Temperature and angular dependence of EPR line width are characteristic of 2D-antiferromagnet. The main exchange interaction in the a b -plane is estimated to be J / k =- 9.5±0.2 K. High field magnetization process and AFMR measurements at low temperatures below T N =78 K showed a spin-flop transition at H c =38.0 kOe. They are satisfactorily explained by assuming the uniaxial anisotropy energy K =1.52±0.10×10 5 erg/cm 3 perpendicular to the a b -plane.

Magnetic properties of ferromagnet-antiferromagnet superlattice structures with mixed-spin antiferromagnetic sheets.

Abstract: We present theoretical studies of the properties of superlattices constructed by alternating films of ferromagnetic and antiferromagnetic materials, each described through use of a localized spin model. The interface between the ferromagnetic and antiferromagnetic constituents is a (110) surface of a bcc lattice. For this system, this geometry places mixed-spin antiferromagnetic sheets adjacent to the ferromagnetic films. The study of the classical ground state as a function of external magnetic field shows that in zero field the ground state has spins canted to minimize total exchange energy at the interface. We find that a different sequence of magnetic-field-induced spin-reorientation transitions occur for various values of the interface exchange constant. For the various phases, we present calculations of the spin-wave spectrum and the infrared absorption spectrum of the superlattice structure.

Anisotropic exchange and spin dynamics in the type-I (-IA) antiferromagnets CeAs, CeSb, and USb: A neutron study.

Abstract: The anomalous anisotropic magnetic interactions and the spin dynamics of the fcc type-I or -IA antiferromagnetic cerium and uranium monopnictides CeAs, CeSb, and USb have been studied by inelastic and diffuse critical neutron scattering experiments. The diffuse scattering above the antiferromagnetic ordering temperature largely corresponds to longitudinal spin fluctuations which are highly anisotropic. In the ordered state the dispersion curves of the spin-wave excitations strongly depend on the actually realized spin structure. For the antiferromagnets the spin waves split into transverse modes with different polarizations due to the exchange anisotropy. In CeAs one of these modes exhibits nearly zero energy gap and quadratic dispersion which has not previously been observed in antiferromagnets. The wave-vector-dependent susceptibility tensor has been calculated within the random-phase-approximation (RPA) by taking account of crystal-field, anisotropic bilinear exchange, and isotropic quadrupolar interactions. General expressions including all levels of the ground-state multiplet are derived for single-q and triple-q type-I as well as for type-IA antiferromagnets, and detailed formulas of the magnetic excitation spectrum are given for the particularly interesting case of effective two-level systems which are often realized in f-electron magnets. The RPA formalism consistently describes the transverse magnetic excitations for T${T}_{N}$ as well as the longitudinal spin fluctuations for Tg${T}_{N}$ for all compounds under study. For CeAs and CeSb the bilinear exchange interactions turn out to be similar, and evidence for important effects of higher-order magnetic interactions is found. The latter are shown to be the driving mechanism for the realization of the various magnetic phases in CeSb. For CeAs the magnetic excitation spectrum unambiguously demonstrates that a collinear single-q type-I spin structure is realized, whereas for USb a noncollinear triple-q type-I spin structure emerges from the observed magnetic excitations.

Magnetic Properties of Intermetallic Compound Mn11Ge8

Abstract: Magnetic properties of an orthorhombic intermetallic compound Mn 11 Ge 8 , which was formerly referred to as Mn 3 Ge 2 , has been investigated on a single crystal specimen at temperatures between 80 K and 800 K. The compound has features of a non-collinear antiferromagnet below T t = 150 K, and makes a spin-flopping transition when magnetized along the c axis. It becomes ferromagnetic with a first order transition at T t with the direction of easy magnetization lying along b axis up to its Curie temperature 274 K. The susceptibility follows the Curie-Weiss law above 550 K, with asymptotic Curie temperature 329 K and effective Bohr magneton number per Mn P eff = 3.26.

Magnetic Properties of Ising-Like Heisenberg Antiferromagnets on the Triangular Lattice

Abstract: It has been pointed out that the effect of competition in interactions (frustration) causes various interesting behaviours in ordering processes [1]. The antiferromagnet on the triangular lattice (AFT) is one of typical models with frustrated interactions. Classical AFT models with various symmetries of spins have been investigated and the natures of phase transitions of them are interpreted through the symmetries of order parameters[2,3].

Structural, electronic, and magnetic properties of Co: Evidence for magnetism-stabilizing structure.

Abstract: Total-energy local-spin-density energy-band calculations are employed to study the different structural phases (hcp, fcc, and bcc) and magnetic states of Co metal as a function of volume. In the paramagnetic state, the fcc phase is lowest in energy with magnetic order stabilizing the hcp phase as the (observed) ground state. Unlike the case of Mn, Cr, and Fe which have stable antiferromagnetic states in the fcc phase, the ferromagnetic state is the most stable for all three phases of Co.

Geometry-Induced Phase Transition in the ± J Ising Model

Abstract: We present an argument for the existence of a geometry-induced phase transition in the ± J Ising model on an arbitrary lattice ( d ≥2) with asymmetric probability of ferromagnetic and antiferromagnetic bonds. This transition manifests itself as a vertical phase boundary separating, possibly, a ferromagnetic and a non-ferromagnetic (paramagnetic or spin glass) phases.

Investigations of nuclear antiferromagnetic ordering in copper at nanokelvin temperatures

Abstract: Nuclear magnetism in metallic copper has been studied by demagnetizing highly polarized spins to low fields where spin-spin interactions dominate. In earlier experiments anomalous spin-lattice relaxation caused by impurities warmed up nuclear spins too fast; this adverse effect was overcome by selective oxidation of impurities. In zero field the critical temperatureT c of the antiferromagnetic transition is 58±10 nK, and during the first-order phase change the entropy increases from (0.48±0.03)ℛ ln 4 to (0.61±0.03)ℛ ln 4. The critical fieldB c =0.27±0.01 mT. The entropy and the static susceptibility of the nuclear spins were measured as a function of temperature whenB=0. These curves agree with theory in the paramagnetic state. In a polycrystalline sample two anomalies were observed at the lowest entropies in the NMR line shapes of the dynamic susceptibility and in the behavior of the static susceptibility. However, when measuring the static susceptibility of a single-crystal specimen in the three Cartesian directions, three different ordered phases were found. These antiferromagnetic states are described and theB-S phase diagram is presented. Metastability and nonadiabaticity are discussed. The observed large reduction ofT c from the mean field calculationT MF=230 nK is caused by fluctuations. The free electron model of the Ruderman-Kittel (RK) interaction seems to be able to explain only one ordered phase. However, relatively small changes to the RK range function or inclusion of non-s-electron-mediated interactions to the Hamiltonian may increase the number of ordered phases to three. Long-living metastable states are another possible explanation for the observations.

Ground State of Antiferromagnetic Quantum Spin Systems on the Triangular Lattice

Abstract: The spin-1/2 antiferromagnetic Heisenberg and X Y models are investigated on the triangular lattice by numerically diagonalizing finite size systems (up to 21 spins). The ground state energies of both models are found to be close to other theoretical predictions except those of Marland and Betts who performed similar analysis to ours. We have numerically constructed a resonating valence bond state of Anderson. It has a relatively large projection on the ground state of the finite Heisenberg model, although the absolute value of the projection decreases linearly with the system size. The trial function proposed by Miyashita for the X Y model does not have an appreciable projection on the numerically exact state. We present evidence for the absence of a sublattice long range order in the Heisenberg model and the existence of the same quantity in the X Y model.

Magnetization Process of the Spin-1/2 Antiferromagnetic Ising-Like Heisenberg Model on the Triangular Lattice

Abstract: The magnetization process at T =0 of the spin-1/2 Heisenberg antiferromagnet on the triangular lattice with Ising-like exchange anisotropy is studied. A comparison is made to a corresponding classical system. A plateau of magnetization has been found for an interval of the external field, on which classical spin configurations dominate. Other than on the plateau, quantum effects invalidate the classical picture. A possibility of experimental confirmation of this classical-quantum crossover is also pointed out.

Magnetic structure and dynamics in the alpha and beta phases of solid oxygen.

Abstract: We describe a comprehensive neutron scattering study of ..cap alpha..- and ..beta..-O/sub 2/. In ..cap alpha..-O/sub 2/, an inelastic feature at 10 MeV is identified with the b(/2 zone boundary, enabling the first measurement of the intrasublattice exchange in this system. We find the intrasublattice exchange constant to be -1.2 +- 0.1 MeV. Taken in conjunction with the intersublattice exchange, -2.4 MeV determined from magnetic susceptibility, we find that the system is very close to a magnetic instability. The ..cap alpha..-phase staggered magnetization drops with increasing temperature, extrapolating to a purely magnetic transition at 31 K, which is 7 K above the ..cap alpha..-..beta.. transition. This is only 40% of the mean-field ordering temperature, implying that the magnetic couplings are predominantly two-dimensional (2D). ..beta..-O/sub 2/ has 2D short-range magnetic correlations. These results are discussed in light of a model of magnetoelastic coupling in a frustrated triangular antiferromagnet.

Alloy-stabilized semiconducting and magnetic zinc-blende phase of MnTe.

Abstract: While MnTe has the stable NiAs structure with a direct band gap of 1.30 eV and a Mn-Te bond length of 2.92 \AA{}, extrapolation of the data for the zinc-blende alloy ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ to $x=1$ suggests an alloy-stabilized MnTe phase with very different properties: a band gap of \ensuremath{\sim}3 eV and a Mn-Te bond length of 2.73 \AA{}. We model the structural, magnetic, and electronic properties of such a hitherto unknown zinc-blende-like MnTe phase through spin-polarized total-energy calculations, and report its unusual properties in both ferromagnetic and antiferromagnetic spin ordering.

Magnetic structure of the heavy-fermion compound U2Zn17.

Abstract: PHYSICAL REVIE%' VOLUME 33, NUMBER 5 Magnetic structure of the heavy-fermion compound MARCH 1986 U2Znt7 D. E. Cox, G. Shirane, and S. M. Shapiro Physics Department, A Tcf T Brookhaven National Laboratory, Bell Laboratories, Upton, New York G. Aeppli 600 Mountain Avenue, Murray Hill, New Jersey 07974 Z. Fisk and J. L. Smith Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 l. Kjems Risd National Laboratory, Roskilde, Denmark H. R. Ott Laboratorium I'ur I estkorperphysik, Eidgenossische Technische Hochschule-Honggerberg, 8093 Zurich, Switzerland (Received 26 September 1985) The phase transition of U2zni7 at 9. 7 K has been investigated by neutron powder diffraction. The transi- tion corresponds to the onset of antiferromagnetic order where the U moments are oriented antiparallel to their nearest neighbors within the basal planes and the near neighbor along the c axis of this rhombohedral compound. At 5 K, the ordered moments lie within the basal planes and are of magnitude (0. 8+0. 1) p, &, which is substantially below the paramagnetic moment of 2.25', &/U atom given by high-temperature sus- ceptibility data. The list of heavy-fermion systems, which display ex- traordinarily large ( & 400m, ) effective conduction electron masses as deduced from the low-temperature specific heat, and metals remaining now includes both superconductors Recent magnetic paramagnetic to the lowest temperatures. susceptibility and specific-heat measurements suggest that there are also heavy-fermion systems which undergo transi- tions to magnetically ordered ground states. ' In this paper, we present the first neutron-scattering determination of magnetic order in a heavy-fermion system, U2Zni7. The essential results are as follows. First, the ordering, which 10 K, is exceedingly simple, with the mag- sets in at T~ netic unit cell identical to the nuclear unit cell, and the mo- ments associated with the two U atoms in the primitive unit cell oriented in opposite directions. Second, the ordered moment is (0. 8+0. 1)p, s/U atom which is well below the moment of 2. 25@, s /U atom deduced from the high- temperature (bulk) susceptibility. U2Zni7 was made by heating the appropriate amounts of U and Zn to 1050'C in an evacuated BeO crucible. Ap- proximately 20 g of material were crushed into a coarse pounder and loaded into a cylindrical aluminum sample hold- er in an atmosphere of helium. Data were collected at the Brookhaven High Flux Beam Reactor with 2.353-A neu- trons from a pyrolytic-graphite monochromator in the (002) filter suppressed higher-order setting. A pyrolytic-graphite wavelengths. For the structure determination at 15 K ( T~), a pyrolytic-graphite analyzer in the (004) setting was used in order to optimize the resolution at higher scattering angles. The collirnations were 20'-open-40'-20' for in-pile, monochromator-sample, sample-analyzer, and analyzer-detector, respectively. The resulting diffraction pattern showed a number of weak impurity peaks in addi- tion to those characteristic of U2Zni7. The major impurity was identified as Zn, estimated to be about 5'/0 by weight. The remaining peaks were an order of magnitude weaker «1% of the strong U2Zn~7 peaks) and (with intensities could not be identified. The d spacings are listed in the cap- tion to Fig. 1, and do not correspond to those of UZni2 or e-U. At room temperature, U2Zn&7 (Ref. 3) has the Th2Zn~7- type structure, which is one of a series of ordered structures [e. g. , Pu3Zn22, UZnt2 (Ref. 5)] which can be derived from that of CaCu5. In U2Zni7, Zn occupies the Cu sites and U is ordered on two-thirds of the Ca sites, the remaining one- third being replaced by pairs of Zn atoms about 2. 6 A apart. The ordered structure has rhombohedral symmetry, space group R3m, with hexagonal lattice constants v 3a and 3c with respect to those of the parent CaCu5-type cell. Be- cause the structural parameters for U2Zni7 near its 10-K transition were unknown, we carried out a Rietveld analysis of the data sho~n in Fig. 1. Regions around the impurity peaks and Al reflections from the sample holder were ex- cluded from the refinement, and background contributions were estimated by interpolation between values obtained by averaging over regions where no Bragg peaks were present. Table I displays the lattice parameters and atomic coordi- nates given by the profile refinement. In the upper frame of Fig. 1, the solid line represents the calculated profile which best fits the data, while in the lo~er frame, the difference between the calculated and observed profiles is shown. The results are in exce11ent agreement with a room-temperature x-ray scattering determination of the structure. Belo~ 10 K some very weak additional scattering at some of the low-angle nuclear peak positions was observed. To gain more intensity tics to be obtained and thus allow adequate counting statis- in a reasonable period of time, the

Magnetic structure and magnetic properties of the spinel solid solutions ZnCr2xAl2-2xS4 (0.85?x?1). I. Neutron diffraction study

Abstract: The spinel solid solutions ZnCr2xAl2-2xS4 have been studied by means of neutron diffraction in the concentration range 0.85

Magnetism of R2Fe14B-based systems☆

Abstract: A review is presented of recent work carried out in the authors' laboratory on alloys based on R 2 Fe 14 B, in which R ≡ Pr, Nd, Dy, Er, Y or Th. These studies have involved substitutions on the rare earth, the iron and the boron sublattices. Many unusual effects have been observed. As one example, the replacement of iron by silicon leads to a rise in Curie temperature. As another, the presence of cobalt in the Nd 2 Fe 14− x Co x B system results not only in a shift in the low temperature spin reorientation (cone to axis) but also triggers, for x ⩾ 10, an appearance of a second spin reorientation (axis to plane) at high temperature. In the Pr 2 Fe 14− x Co x B system, for x ⩾ 9.5, a high temperature spin reorientation (axis to plane) was also discovered. Variation of the spin reorientation temperature was determined for different rare earth systems in which iron was substituted by cobalt, ruthenium, gallium and silicon respectively. The dependence of the spin reorientation temperature in Er 2− x R x Fe 14 B (R ≡ Y, Ce, Pr, Gd and Th) on R content was determined. In the Er 2− x Th x Fe 14 B system two spin reorientations are observed in the 0.75 ⩽ x ⩽ 1.25 composition range. Replacement of boron by carbon in dysprosium- and erbium-based compounds leads to a drop in magnetization, Curie temperature and magnetic anisotropy.

A high resolution neutron diffraction study of the perovskite LaTiO3

Abstract: LaTiO3 shows a transition from temperature-independent paramagnetism to antiferromagnetism at 125 K. The temperature coefficient of the electrical resistivity changes at the same temperature from positive (i.e. metal-like) to negative (i.e. semiconductor-like). The crystal structure of LaTiO3 was investigated at five temperatures from 298 K to 10 K by time-of-flight neutron diffraction to look for any structural origin to the above phenomena. Analysis of the 298 K data confirm and improve on an existing X-ray structure determination in Pbnm. The same orthorhombic cell and space group are consistent with the data at all temperatures studied. The cell constants show anisotropy as b and c decrease with temperature and a increases slightly. There are no significant changes in Ti-O bond lengths or Ti-O-Ti angles with temperature. In the La-O polyhedron the eight nearest-neighbour bond distances decrease with decreasing temperature while the next four increase demonstrating a tendency to eightfold coordination. There is no structural anomaly of any significance near 125 K. This is not inconsistent with an itinerant antiferromagnetic model for the transition.