P. F. de Châtel

• New Mexico State University

The deterministic Landau-Lifshitz-Gilbert equation has been used to investigate the nonlinear dynamics of magnetization and the specific loss power in magnetic nanoparticles with uniaxial anisotropy driven by a rotating magnetic field. We show that a more efficient heat generation by magnetic nanoparticles is possible if the direction of the rotati...

An alternative approach in the estimation of the magnetic field generated by atomic current densities is presented and applied to both the orbital and spin magnetic hyperfine fields of tri-positive rare earth ions. The application of the formulae offered is tested on the free ions Dy3+, Er3+ and Yb3+ in their ground states. The estimated magnetic h...

The numerous phenomenological equations used in the study of the behaviour of single-domain magnetic nanoparticles are described and some issues clarified by means of qualitative comparison. To enable a quantitative \textit{application} of the model based on the Debye (exponential) relaxation and the torque driving the Larmor precession, we present...

The equation of state, structural behavior and phase stability of {\alpha}-uranium have been investigated up to 1.3 TPa using density functional theory, adopting a simple description of electronic structure that neglects the spin-orbit coupling and strong electronic correlations. The comparison of the enthalpies of Cmcm (alpha-U), bcc, hcp, fcc, an...

A formalism is presented that enables the calculation of atomic charge and current densities in Russel–Saunders states of free atoms and ions in terms of scalar and vector spherical harmonics. The electric and magnetic fields generated by the multipole components of charge and current distributions are easily calculated. They are found to have the...

The mechanism of magnetization reversal in single-domain ferromagnetic particles is of interest in many applications, in most of which losses must be minimized. In cancer therapy by hyperthermia the opposite requirement prevails: the specific loss power should be maximized. Of the mechanisms of dissipation, here we study the effect of Néel relaxati...

The mechanism of magnetization reversal in single-domain ferromagnetic particles is of interest in many applications, in most of which losses must be minimized. In cancer therapy by hyperthermia the opposite requirement prevails: the specific loss power should be maximized. Of the mechanisms of dissipation, here we study the effect of Neel relaxati...

Emission and transmission Mössbauer studies of La 0.8 Sr 0.2 CoO 3-δ< /Subscript> perovskites doped with ∼0.02 stoichiometric units of oxygen vacancy or 2.5% iron corroborate the occurrence of electronic phase separation in these systems. The effect of the small perturbation of the CoO 3 sublattice with either iron ions or oxygen vacancies on the b...

The enhancement and extinction spectra for fractal aggregates consisting of monodisperse nanosized silver particles are studied theoretically. We find the iterative solution to the coupled-dipole equations in the quasistatic approximation, taking into account a contribution of the nonlinear susceptibility χ(3) to the intensity-dependent dielectric...

The paramagnetic susceptibility measured on La1−xYxSr2−yCay Mn2O7 (x, y or z=0, 0.03 and 0.1) manganites does not obey the Curie–Weiss law. The Curie constant exceeds the expected values by more than order of magnitude. Based on strong disorder we have compared the experimental data with predictions based on Griffith's singularity model. We find th...

We report on the electronic properties of a U Ni _1/3 Ru _2/3 Al single crystal as a function of temperature and magnetic field. Our specific-heat, magnetization, and resistivity data provide strong evidence that the uranium 5f moments order ferromagnetically below T_C=74 K . Magnetic measurements reveal that the c a...

Results of dc magnetization, ac susceptibility and magnetotransport measurements on Eu0.8Sr0.2CoO3 are presented. The compound shows glassy ferromagnetic character. The compound is semiconducting-metallic with negative magneto-resistance.

Probability and spin densities for rare-earth tri-positive ions in their ground states are calculated using irreducible tensor operators and Racah double tensors, which enable an expansion of the densities in (vector) spherical harmonics. Graphical representation of such densities reveal characteristic features lost in schematic shapes predicted by...

We study the effect of a non-magnetic defect on the properties of the s=12 two-dimensional Heisenberg antiferromagnet with honeycomb lattice at T=0. A modified Oguchi method is used to calculate the moment reduction and nearest-neighbour correlations for clusters of up to 13 spins embedded within the molecular field of the remainder of the lattice....

Below TN=50 K, UNiGe exhibits incommensurate (INC) antiferromagnetic (AF) order with an additional order-order (AF) phase transition at TM=42.5 K. The ground-state AF structure is characterized by a propagation vector (0,1/2,1/2). At 4.2 K, there are two field-induced transitions at 17 and 25 T for the b-axis and at 3 and 10 T for fields along c. N...

The toroid dipole moment is suggested as a possible order parameter relevant to some unusual phase transitions in U and Ce compounds. It is shown that toroid dipole moments can only occur in mixed-valence states so that their observation would be a signature of valence mixing, i.e., hybridization. Application of these ideas to URu2Si2 does not seem...

Charge, current and spin densities are calculated for a two-electron system, maintaining the explicit form of the wave functions, in terms of Slater determinants. The two-electron Russell–Saunders spin–orbit coupled eigenstates |L,S,J,MJ〉 are expressed as four-component spinors, and the operators of the above densities as 4×4 matrices. The contribu...

Recent results and extensive background information on a number of heavy-fermion compounds serve to illustrate the phenomena and concepts involved. The large mass enhancement common to these materials is seen to signal the importance of strong correlation, which, more often than not, leads to a departure from the Fermi-liquid state. The resulting '...

The unusual, strong temperature dependence of the low temperature electrical resistivities of the Ni3Al and Ni3Ga intermetallic phases are analysed in terms of existing theories of scattering of conduction electrons by spin-density fluctuations. A qualitative agreement between theory and experiment is found but none of the theories can adequately d...

Empirical correlations are established, which demonstrate that the heat of formation of metallic binary alloy systems is predominantly determined by the electronegativity difference, the difference in electronic density at the boundary of the atomic cell and the size difference, the third term being absent for compounds. The work function of a meta...

Results of specific heat measurements between 1.5 K and 15 K on a large number of alloys in the range of existence of the Ni3Al and Ni3Ga intermetallic phases are reported. For four Ni3Ga samples the measurements were extended down to 0.2 K, and the effect of various heat treatments on the specific heat was measured on two Ni3Ga samples. The result...

The selfconsistent charge density is calculated by means of the density functional formalism using a local exchange-correlation potential for a simple jellium model of a divalent impurity and a vacancy in a monovalent host. The resulting charge density around the impurity does not lend itself to an interpretation in terms of a surface dipole layer,...

The low-temperature thermoelectric force of AuY, AuZr, AuNb, AuRh, AuPd and AuPt has been measured between 1.5 and 16K. Besides a linear electron diffusion term in the thermoelectric power, that is independent of concentration the authors have found a negative T3 term for the as-drawn wire samples, and a mostly stronger positive T3 term below 4K fo...

For pt.I see ibid., vol.14, no.9, p.2061 (1984). The low-temperature thermoelectric power and resistivity measurements of the preceding paper on dilute AuY, AuZr, AuNb, AuRh and AuPd alloys are analysed in a free-electron model to give s, p and d scattering phase shifts. The virtual bound-state parameters obtained from this analysis show that the l...

The authors have calculated the resistivity, caused by the scattering of free electrons on an impurity described by a localised potential with cubic symmetry in terms of phase shifts (l<or=2), using an exact solution of the linearised Boltzmann equation and an approximation to the solution consisting of four cubic harmonics with t1z symmetry. The l...

The current densities in partially filled electron shells of free atoms or ions, when analyzed in terms of multipole expansions, do not carry signatures that would distinguish orbital and spin currents. The same holds for the orbital and spin contributions to elastic neutron scattering amplitude, which are related to Fourier transforms of the respe...

The theory of the elastic magnetic scattering of neutrons on atoms and ions is well established and is easily extended to account for the effect of crystal fields. Weak crystal fields, which do not break up the spin-orbit coupling, can reduce the orbital moment, but do not change the ratio of orbital to spin moments. When a strong crystal field aff...

The current density and magnetization is calculated in the ground state and the lowest-lying 4f state of a hydrogen atom. The ambiguity of the magnetization inherent in the gauge freedom in the defining equation curlM=j is shown to allow widely different and often unphysical patterns. The commonly used Trammell gauge and the recently recommended mo...

The magnetic field generated by an electron bound in a spherically symmetric potential is calculated for eigenstates of the orbital and total angular momentum. General expressions are presented for the current density in such states and the magnetic field is calculated through the vector potential, which is obtained from the current density by dire...

We have determined a set of crystal-field parameters for CePtSn which accounts for the available susceptibility, high-field magnetization at 4.2 K and inelastic neutron-scattering data. The analysis of experimental data revealed that the single-ion approach is reliable mainly at high temperatures (T>or=TN, TK) or at high magnetic fields where the e...

UNiGe crystallizing in the orthorhombic TiNiSi-type of structure orders magnetically below TN = 50 K with an additional magnetic phase transition at 42 K. Both structures (below 42 K commensurate antiferromagnetic, between 42 K and TN incommensurate) are non-collinear with a significant a-axis component (μx = 0.35μB/U at 20 K). The magnetic propert...

Spin structures in the presence of an external magnetic field have been studied for the two-sublattice model. The field dependence of the spin configurations has been found to depend sensitively on the competition among the exchange and the anisotropies of the two sublattices. Four kinds of magnetization processes have been identified in the ferrim...

Some surprizing facts about simple structures and simple facts about complicated structures are reviewed with the aim of introducing the important concepts, terminology and symbols used in this field.

A simple two‐sublattice model is used to analyze the magnetization process of anisotropic antiferromagnets at T=0. The magnetization is calculated for samples free to be oriented by the applied field (free single crystals or powders consisting of single‐grain particles). We find that the anisotropy does not necessarily lead to a nonlinear M(B) rela...

The tetragonal intermetallic compounds U2Ni2In and U2Rh2Sn have been studied by means of specific-heat, electrical-resistivity, and neutron-diffraction techniques. At low temperatures, both compounds order antiferromagnetically in a magnetic unit cell doubled along the c axis, and we find 5f moments of 0.60 and 0.38μB/U atom for U2Ni2In and U2Rh2Sn...

The spin configurations in the absence of an external magnetic field have been systematically investigated for a two-sublattice system. Based on a two-sublattice model, the conditions for the existence of collinear and non-collinear spin structures were derived for either ferromagnetic or ferrimagnetic materials and the phase diagrams of the spin c...

The Er-Co exchange interaction, JErCo, and the magnetic anisotropy in Er2-xYxCo7B3 compounds with x = 1.4, 1.5, 1.7, 1.9 and 2.0 have been investigated by measuring the free-powder magnetization at 4.2 K. Magnetic transitions are found in the Y-rich compounds. A model description is presented to explain the rotation processes in the Er- and Co-subl...

The free-powder (monocrystal) magnetization of ErY2Co11B4 has been studied at 4.2 K in the Amsterdam High-Field Facility in fields up to 35 T. A metamagnetic transition is found. The magnetization process in this compound can be explained in terms of a two-sublattice model taking into account the Er- and Co-sublattice anisotropy, and the Er-Co exch...

Interstitial nitrides of the type LaFe13 − xAlxNy have been synthesized and their magnetic properties have been investigated. It is found that the magnetic properties are drastically modified by the introduction of interstitial nitrogen. The physical origin of the changes is discussed.

The band widths of several UTX and U2T2X compounds (T: transition metal, X: p-metal) are evaluated by means of a tight-binding method. The magnetism in both groups of compounds is governed by the hybridization between U f-states and transition-metal d-states. Comparing the sum of all hybridization effects, we find approximately the same hybridizati...

A detailed investigation of the structure and magnetic properties of Er2Fe17Cx compounds is presented in this paper. The interstitial carbides Er2Fe17Cx with x=0.0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 have been synthesized by arc melting and by the gas-phase-interaction method. The unit-cell volume of the compounds is found to increase with increasing...

The enormous magnetoresistance effect at low temperatures in various uranium‐based intermetallic compounds, which exceeds by far the effect found in magnetic‐multilayer systems, is a consequence of the strong 5f conduction electron hybridization. The consequences of spin‐dependent scattering for the giant magnetoresistance (GMR) effect in uranium i...

The ternary compound UNiAl, crystallizing in the ZrNiAl-type structure, is an itinerant antiferromagnet with magnetic moments of less than 0.8muB per U atom and with a high gamma value of 164 mJ/mol K2. The anisotropic response of the electronic properties to magnetic field is closely connected with the huge uniaxial magnetic anisotropy, observed n...

A review is given of the experimental values of the magnetic intersublattice-coupling constants in rare-earth (R) — transition-metal (T) intermetallics, derived from high-field magnetization measurements on single-crystalline powder particles that are free to be oriented by the applied magnetic field. The results are compared with values for the in...

A non-logarithmic time dependence of the magnetization relaxation in superconductors is modeled by certain solutions of the nonlinear equation for flux diffusion, which can be derived either on the assumption of a logarithmic dependence of the pinning potential on the current density or, equivalently, a power-law current-voltage characteristic. Lim...

Magnetization measurements up to 35 tesla have been performed on compounds of the series R₂Co₁₇ and R₂Co ₁₇N_x (R=rare earth) on particles free to be oriented by the applied field. The magnetic coupling in these compounds has been derived from the magnetic isotherms at 4.2 K by means of a two-su...

Magnetization measurements up to 35 tesla have been performed on compounds of the series R2Co17 and R2Co 17Nx (R=rare earth) on particles free to be oriented by the applied field. The magnetic coupling in these compounds has been derived from the magnetic isotherms at 4.2 K by means of a two-sublattice model in the mean-field approximation. It is f...

The anisotropy in the basal plane is taken into account in the investigation of the magnetic exchange interaction between rare-earth (R) and transition-metal (T) sublattices of ferrimagnetic R-T intermetallic compounds. As a result of the non-zero basal-plane anisotropy, an oscillating magnetization curve is predicted.

As part of a systematic research programme on equiatomic ternary compounds of the type RTX (R is a rare earth, T a transition metal and X a metal out of the p block of the periodic table crystallizing in the ZrNiAl structure, results for CePdxRh1-xIn (x = 0, 0.2, 0.4, 0.6, 0.8, 0.85, 0.9, 0.95, 1) are presented. The magnetic properties, specific he...

Using a sensitive Hall probe, the magnetization relaxation of Bi2Sr2CaCu2O8 single crystals has been measured accurately. The sample was cooled down from T>Tc in a large bias magnetic field and then relaxation has been registered after a small change of the magnetic field. The effects of the bias field value, ranging from almost zero up to Hirrev (...

Magnetization curves have been calculated for single crystals of ferrimagnetic rare‐earth transition‐metal compounds that are free to rotate in the applied magnetic field. The calculations have been performed taking into account the magnetic‐anisotropy constants of the rare‐earth and transition‐metal sublattices up to the fourth order. Seven differ...

Magnetization measurements on free (monocrystalline) powder samples of ferrimagnetic rare-earth (R) transition-metal (T) compounds provide an excellent possibility to determine the strength of the R-T exchange coupling. This is very simple if the magnetocrystalline anisotropy of the R-sublattice is large in particular and the T-sublattice anisotrop...

The Symposium materials contain 109 papers dealing, among others, with the subjects that fall outside the traditional scope of meetings on magnetism. These are various aspects of semiconductor physics, including heterostructures and quantum wells, superconductivity and quantum oscillations. Magnet technology, high-temperature superconductivity, D-m...

Low-field AC susceptibility measurements have been carried-out on single-crystalline samples of the unconventional superconductor UPt3 and on UPt3 doped with 11% boron. Both components of the susceptibility, chi' (T) and chi'' (T) have been found to depend strongly on the AC field amplitude, on the superimposed DC field (up to 200 Oe), and on the o...

Specific heat measurements on UNiAl in magnetic fields up to 20 T demonstrate that the Neel temperature (T(N) = 19 K) is drastically reduced by magnetic fields B parallel-to c-axis. AF ordering disappears for B > 11.35 T, the field of the metamagnetic transition. A step in gamma-versus B (to congruent-to 250 mJ/mol K2) observed just above the criti...

In magnetically ordered intermetallics of uranium with d transition elements, the magnetic moment on the uranium site is often limited to values below 0.1μ B , with, in some cases, extremely large magnetic anisotropies. Several approaches are followed for explaining these small uranium moments: opposite directions and almost compensation of the spi...

Results of specific heat and magnetoresistivity measurements on Ce(Pd1-xAgx3 will be presented. Arguments will be given to the effect that the high gamma value found for Ce(Pd0.87Ag0.13)3 may be regarded as an intrinsic property, and not due to trivalent Ce ``impurities''. The results will be discussed in terms of a pronounced lowering of the Kondo...

The susceptibility of samples of CePd3±x (x=0.0, 0.1) shows an upturn at low temperatures. Magnetization measurements in high magnetic fields strongly indicate that this behaviour is intrinsic to CePd3 and not due to the spurious presence of magnetic impurities.

To explain the structure, found in neutron scattering experiments on CeAl2, Thalmeier and Fulde recently proposed a model involving a bound state between a crystal field excitation and a phonon. The consequences of this model for static susceptibility and magnetization are presented and compared to experimental data on CeAl2. The results seem very...

After a discussion of the relation between valence and atomic volume, some of the crucial information provided by high-pressure experiments on the Kondo-mixed-valence transition in dilute alloys is presented. The nature of the mixed-valent ground state and the dependence of its energy on the atomic volume is discussed in the light of the results Ra...

The perturbation treatment of the asymmetric Anderson model in the U → ∞ limit is shown to lead to a description of mixed-valent compounds in terms of Landau's Fermi liquid theory. The quasi-particle interaction is independent of spin, and hence the ratio between the low-temperature susceptibility and specific heat is the same as in a Fermi gas.

Crystal field effects have been observed by Lüthi and Ott in the thermal expansion of both cubic rare earth compounds1 and hexagonal rare earth compounds.2 In the case of hexagonal compounds they were ascribed to the coupling between the strains and the quadrupolar operators of the magnetic ions only, while in the case of cubic symmetry, a coupling...

Results are presented on the magnetic susceptibility of a number of Yb intermetallic compounds, where Yb is either divalent or, as will be argued, in an intermediate-(mixed)-valence state. Low-temperature upturns in the susceptibility are ascribed to impurities, for which corrections are made under the assumption that only Yb2O3 is responsible for...

The magnetic and other properties of compounds in which rare‐earth elements occur with an intermediate valence are reviewed. A distinction between ’’metallic’’ and ’’covalent’’ systems is suggested. Strong similarities are found between mixed‐valent materials, particularly of the metallic kind, and transition‐metal or actinide systems which are rea...

General arguments are formulated that strongly suggest that the conduction-electron mediated indirect interaction between spins in a heavily disordered (e.g., amorphous) metal is not exponentially damped, and the mean free path is not a measure of the range of the interaction. The shortcomings of the exponentially damped form pointed out by de Genn...

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Experimentally observed properties of mixed-valent intermetallics are summarized. A model involving noninteracting fermions occupying (2J + 1)-fold degenerate resonance states is found very successful in reproducing the salient features of the experimental results. It is suggested that the key to this success lies in the existence of fermion-like q...

A semi-empirical model of alloy cohesion involving two material constants for each element is introduced by means of the physical ideas underlying the scheme. The resulting expressions for the heat of formation of binary alloys are presented and their applicability in various extreme situations is discussed. The model is shown to reproduce a vast a...

The temperature dependence of the susceptibility for 1.6 K < T < 1100 K and the field dependence of the magnetization in fields up to 35 T show the quasibinary CeInxSn3-x compounds to be homogeneously intermediate-valent for x ≤ 1.9. There is an inverse proportionality between Tmax, the position of the susceptibility maximum, and χ(T = 0). For x >...

A review is given of the various types of changes in magnetic properties due to hydrogen absorption observed in certain groups of intermetallic compounds. These comprise compounds of 3d transition metals in which the second component is one of the strongly hydrogen attracting metals such as Ca, Y, the rare earths, Sc, Ti, Zr, Hf or Th. The changes...

The heat of formation of binary intermetallic compounds of transition metals and the heat of mixing of liquid alloys in general can be predicted by means of a phenomenological model. The ″macroscopic atom″ approach can be used to obtain values for a variety of energy effects in metal physics (surface energies at the metal-vacuum surface, interfacia...

The large magnetostriction of rare earth materials is due to the orbital moment of the 4f electrons, which can result in an aspherical charge distribution, coupled to J, and hence to the magnetic moments on the rare earth ions. Nicholson et al.1 have shown that this single-ion mechanism makes the most important contribution to the magnetostriction...

Yb1−xYx CuAl with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9, 0.99 and 1.0 and Yb0.99Gd0.01 CuAl samples were prepared by the methods known to produce perfectly ordered, single phase YbCuAl. The susceptibility between helium and room temperatures and the magnetization at helim temperature in fields up to 34 T were measured for the whole series. The r...

27Al NMR shifts and spin‐lattice relaxation times have been measured in the intermediate‐valent compound YbCuAl over the temperature range 4.2 K to 295 K. Above Tmax?25 K, the temperature for which the bulk susceptibility χ exhibits a maximum, a linear relation was observed between K and χ: K=7.5(5) ×10−4−0.19(1) χ (emu/mole). For T<Tmax this relat...

Out of 17 binary and 2 ternary ytterbium intermetallics, in the five systems, YbGa2, YbCu2, YbAl2, YbAl3 and YbCuAl an intermediate valency was found. The χ(T) curves for these compounds have a common functional form with a characteristic temperature Tmax. No tendency to saturation is observed in the magnetization at 1.4 K in fields up to 330 kOe.

We present a computer program in Algol 60 by means of which enthalpy effects can be calculated for binary alloys in which at least one transition metal is involved. Predictions can be made by means of this program for seven fixed ordered compositions in the solid phase and for the two limiting heats of solution and the heat of mixing at the equlato...

Seventeen binary and some ternary intermetallic compounds of Yb were examined in order to determine the factors controlling its valency. From susceptibility measurements between 1.4 and 1060°K the trivalent state can be firmly established by the validity of the Curie-Weiss law in 7 systems. Diamagnetism or weakly temperature dependent paramagnetis...

Heats of formation are calculated for heterovalent alloys represented by a jellium model as previously described by the authors (see ibid., vol.5, p.1502, 1975). A much wider range of systems is considered than in the previous work and an attempt is made to identify the parameters governing alloy heats of formation. These parameters are compared wi...

We have extended the Ramirez-Falicov model of the α-γ phase transition of cerium, allowing for a field-induced or spontaneous splitting of the bands and of the six-fold degenerate 4f level. To this end, we had to introduce two new parameters in the theory to take account of conduction electron-f electron and conduction electron-conduction electron...

The Ramírez-Falicov model of the α-γ phase transition of cerium is extended, allowing for a field-induced or spontaneous splitting of the bands and of the sixfold degenerate 4f level. The effect of presently available magnetic fields on the α-γ transition temperature in cerium is found to be negligible. With higher values (not appropriate to cerium...

The experimental finding that the susceptibility of some ZrZn2-type specimens above the Curie point follows the Curie—Weiss law over a limited temperature range is shown to be compatible with the theory of very weak itinerant ferromagnetism.

A generalized form of the Edwards-Wohlfarth theory of very weak itinerant ferromagnetism is derived by allowing for the magnetization dependence of the molecular field parameter kBθ′. The analysis of the magnetic isotherms of paramagnetic Ni3Ga compounds shows that, due to the strong enhancement of the susceptibility, the effects of the change of k...

The pressure dependence of the Néel temperature of chromium-vanadium alloys with less than 3 at % vanadium was determined by electrical resistivity measurements under hydrostatic pressure up to 3000 atm. The Néel temperature of each alloy varies linearly with pressure in the observed range, with a slope proportional to its value at p = 0 atm. The r...

The current denstity generated by electrons in Russell-Saunders states within an l^n manifold comprises only even-parity multipoles: 'magnetic' dipoles, octopoles, etc. (L=1,3,...) and 'electric' quadrupoles, etc. (L=2,4,...). If inversion symmetry is broken, e.g., by an odd-parity order parameter, and hybridization between states of different pari...

On passe en revue les expériences qui appuient les théories du paramagnon. La résistivité électrique à basse température présente des effets de paramagnon prononcés tandis que les mesures de chaleur spécifique ne sont pas en accord avec la théorie. On s'attend à ce que les effets sur l'aimantation à basse température soient trop petits pour être ob...