Crystalline Field Effects Research Articles

Electrical and magnetic properties of light rare-earth Heusler single crystals RInCu2, R=La, Pr, Nd, and Sm

Electrical resistivity ρ and magnetic properties of light rare-earth Heusler single crystals RInCu2, R=La, Pr, Nd, and Sm, have been measured in the temperature range 1.3–300 K. No anomalies due to magnetic transitions were found in the temperature dependence of ρ and magnetic susceptibility χ above 4.2 K. Pr and Nd Heusler compounds have large negative paramagnetic Curie temperatures −19 and −29 K, respectively. The temperature dependence of χ is discussed on the basis of the crystalline field effect. For Sm compound, χ(T) is discussed by means of Van Vleck paramagnetism.

Crystalline-field effect in the intermetallic compound SmCu 2

The anisotropic temperature dependence of magnetic susceptibility and electrical resistivity and the low temperature specific heat have been measured in the orthorhombic intermetallic compound SmCu 2. The anisotropic temperature dependence of the susceptibility is explained well by the theory on the basis of the modified point charge model of the trivalent Sm ions.

Anisotropic resistivity of CePt 2Si 2

The resistivity ϱ of single crystal cerium Kondo compound CePt 2Si 2, measured from 0.1 to 300 K, is found to be strongly anisotropic. The anisotropy of ϱ can be explained in terms of the resonant scattering model describing the influence of the crystalline field effect on the Kondo effect.

Resistivity and magnetic susceptibility of superconducting and non-superconducting ErBa 2Cu 3O 7− y

The oxide ErBa 2Cu 3O 7− y has been obtained in the orthorhombic and the tetragonal forms by suitable heat treatments. The orthorhombic form is metallic and superconducting with T c=88 K while the tetragonal form has high resistance and is non-superconducting. Magnetic studies on both types of compounds reveal that the rare earth ion moment is very close to its free ion value independent of the structure. In the tetragonal compound, deviations in the susceptibility from the Curie-Weiss behavior are noted at low temperatures which may be due to the effect of crystalline electric fields.

Thermal conductivity of cerium compounds.

The third-order perturbation-theory thermal conductivity is computed in the framework of the effective exchange Hamiltonian which describes both the resonant-scattering character and the crystalline field effect of cerium. The model is applied to the thermal conductivity measurements of cerium compounds and good agreement is found for ${\mathrm{CeAl}}_{2}$ and ${\mathrm{CeCu}}_{2}$${\mathrm{Si}}_{2}$.

Thermal, Electrical and Magnetic Properties of the Ferromagnetic Dense Kondo System CeSix

Single crystals of the ferromagnetic dense Kondo system CeSi x were grown, and the specific heat, the electrical resistivity and the magnetic susceptibility were measured. Electrical resistivity measurements clearly show the typical Kondo behavior, which unambiguously tells that CeSi x is a ferromagnetic dense Kondo system. The appreciable anisotropy of the magnetic susceptibility is analyzed with the crystalline field effect and a conjecture is made that the ground doublet is a \(\varGamma_{7}\)-like doublet.

Spin-disorder resistivity in the paramagnetic state of the heavy rare-earth dihydrides.

We present systematic measurements of the paramagnetic spin-disorder resistivity ${\ensuremath{\rho}}_{m}$ in Gd, Tb, Dy, Ho, and Er dihydrides. We observe that ${\ensuremath{\rho}}_{m}$ is strongly affected by crystalline-field effects especially as concerns ${\mathrm{DyH}}_{2}$ and ${\mathrm{ErH}}_{2}$. The absolute values of ${\ensuremath{\rho}}_{m}$ are much smaller than in the corresponding pure metals, an effect which can be attributed in part to modifications, with hydrogen, of the electronic band structure, but it implies also a reduction of the fundamental exchange interaction between conduction and localized electron spins.

Observations of magnetic and structural ordering in TbH2+x compounds through electrical resistivity measurements.

We present detailed resistivity measurements rho(T) in the magnetically ordered state of TbH/sub 2+//sub x/. Three types of behavior are observed: (i) for xapprox. =0, we find a classical antiferromagnetic transition with a well-defined drop of the spin-disorder resistivity below T/sub N/approx. =18 K; (ii) for x>0, the total resistivity rho(T) goes progressively through a minimum and a maximum with decreasing temperature, indicating an incommensurate type of ordering which starts at temperatures above T/sub N/; (iii) for xgreater than or equal to0.15 and for samples presenting a structural transition within the H sublattice, we observe a sharp transition at 38 K, with a smoother minimum at about 55 K. These results can be at- tributed to modifications of the electronic structure and of the mean free path with x, and to the existence of uniaxial crystalline field effects related to structural short-range and long-range order in the H sublattice.

Effective Hamiltonian fitting of the crystalline field effects for rare earth ions of [formula omitted] in cubic symmetry

The importance of adding an eighth-order operator to improve the description of the crystal field splitting for rare earth ions with J = 15 2 is examined through a fitting of the experimental data for M:Er 3+ (M = Ag, Cu, Zn) and MeF 2:Dy 3+ (Me = Ca, Sr, Ba, Cd). The added terms allow for a fairly good agreement with the experimental data in the case of ionic systems while in the case of metallic hosts they do not add any improvement to the fitting.

Depression of the superconducting transition temperature of the Heusler alloy Pd2YSn with the addition of magnetic rare-earth metals.

The compound ${\mathrm{Pd}}_{2}$YSn, having the cubic Heusler L${2}_{1}$ structure, is superconducting with a transition temperature (${T}_{c}$) of 4.55 K. The effect on ${T}_{c}$ of replacing Y by other magnetic rare-earth metal has been investigated in the series ${\mathrm{Pd}}_{2}$${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{R}}_{\mathrm{x}}$Sn (R=Gd, Dy, Ho, Er, Tm, and Yb). The depression in ${T}_{c}$ is the largest with Gd substitution. The initial rate of depression of ${T}_{c}$ shows deviation from the de Gennes function. The results of ${T}_{c}$ measurements are analyzed in terms of Abrikosov-Gor'kov theory, taking into account the effects of crystalline electric fields acting on rare-earth ions. Values of the density of states times the exchange constant, [N(0)${J}_{\mathrm{sf}{}^{2}}$], are derived from these measurements.

Crystalline field and kondo effect in CeBi1-xTex

Abstract Magnetic and transport properties on CeBi 1- x Te x solid solution are reported. For 0.125 ≲ x ≲ 0.3, the long range magnetic ordering seen for x ⩽ 0.1 diappears and the spin glass freezing is observed. The crystal field splitting for x ⩾ 0.1 is estimated to be ≈ 40 K with Г 7 ground state from the thermal dilation. These are well explained within the p-f mixing model.

Magnetic properties of CeCd and NdCd single crystals

Abstract Ferromagnetic properties of NdCd single crystals are well understood by taking into account the crystalline field effect. While the susceptibility of Ce 0.2 La 0.8 Cd is quantitatively interpreted by taking Γ 8 as the ground state, the magnetic properties of CeCd single crystals suggest that the Ce-ion in condensed CeCd is no longer a well defined Ce 3+ ion.

Magnetic properties of anomalous rare-earth intermetallic compounds

We present here theoretical results which describe some magnetic properties of anomalous rare-earth intermetallic compounds, with a special emphasis on neutron diffraction experiments. We describe two theoretical models, both the Kondo model including crystalline field effects, and the spin-fluctuation model and we discuss some relevant experiments explained by these models.

Magnetic susceptibility and Verdet constant in rare earth trifluorides

On three fluorides CeF3, NdF3, and PrF3 accurate susceptibilities measurements are reported from 2 up to 300 K under a magnetic field applied along the c axis. On the same samples, the optical Faraday rotation has been investigated in the temperature range 8–300 K at 0.6328 μm wavelength in a magnetic field up to 20 kOe. The reciprocal susceptibilities χ−1(T) follow a Curie Weiss law for T>100 K; the observed values of the paramagnetic Curie temperature are − 56 K (PrF3), − 114 K (CeF3), and − 26 K (NdF3). For T<100 K, strong crystalline field effects are evidenced: for example, a maximum of χ near 60 K has been found in PrF3. In the three fluorides negative Verdet constants have been obtained. The ratio V/χ appears as strongly temperature dependent, that is quite different from the theoretical prediction. Furthermore, the experimental results show an evidence of two behaviors of V/χ for T>77 K. (V and χ are expressed in deg cm−1 Oe−1 and in μB mol−1 Oe−1, respectively.) On one hand for NdF3 and PrF3, it has been found V/χ =A(1+αT) where A is a constant (−4320 in NdF3; −7241 in PrF3); in both samples, α is in the order of −6×10−4 K−1, note that Faraday rotation measurements performed at 0.4579 and at 0.5017 μm lead to an identical α value. On the other hand in CeF3, V/χ is a linear function of T−1 and is given by 13700(1+75.9/T).

A 14N NMR study of tetraalkylammonium compounds in the solid state

The 14N NMR powder patterns of various quaternary ammonium salts have been measured over the temperature region 155 to 273°K. Some of the spectra are dominated by motion, while others appear to arise from a rigid lattice; from the latter, values of the quadrupole coupling constant ( e 2 gQ) and the asymmetry parameter η are determined. The quadrupole coupling constants fall in the range commonly observed for deuterium, while the asymmetry parameters take on virtually all possible values from 0 to 1. For some compounds the parameters appear to derive completely from lattice (crystalline field) effects, while for others there is probably a combination of lattice and intramolecular effects.

29Si nuclear magnetic resonance and relaxation in the paramagnetic state of CeCu 2Si 2

29Si nuclear magnetic resonance (NMR) and relaxation studies of the unstable-moment compound CeCu 2Si 2 have been carried out to probe the electronic state of the nearly-trivalent Ce ions. Isotropic and anisotropic NMR shifts indicate effects of both crystalline electric fields (CEF) and low-temperature moment reduction on the Ce ionic states. A relatively large anisotropic shift was observed at low temperatures, and also obtained from a CEF-state calculation in the molecular-field approximation. The hyperfine coupling also appears to be anisotropic, although this is not manifested in the temperature dependence of the shift due to changing CEF-state populations. NMR estimates of the Ce-spin fluctuation time vary with temperature in a manner similar to the neutron quasielastic scattering linewidth at high temperatures, but suggest the onset of spatially coherent fluctuations.

Spin reorientation in ( HoxY1− x) Co2 and ( NdxY1− x) Co2 systems (1 ⩾ x ⩾ 0.7)

Among the rare earth-Co 2 Laves phases, HoCo 2 and NdCo 2 show a spin reorientation at about 15 and 43 K, respectively. At low temperature in both compounds the easy direction of magnetization is [110]. On heating up the samples the easy direction changes to [100] at the temperatures given above. Such a spin reorientation is explained by the combined effect of crystalline field and exchange interaction. The aim of this paper is to present theoretical calculations and experimental results concerning the influence of replacing the magnetic rare earth ions in HoCo 2 and NdCo 2 by non-magnetic Y on the spin reorientation temperature. It was found that the spin reorientation temperature decreases in (Nd, Y)Co 2 and increases in (Ho, Y)Co 2 with increasing Y concentration. Experimental data obtained from resistivity measurements are compared with theoretical results.

133Cs Quadrupole Perturbed NMR Study of Jahn‐Teller Phase Transitions in CsCuCl32)

Abstract133Cs nuclear spin‐lattice relaxation measurements in CsCuCl3, in the temperature range 100 to 700 K, and an analysis of the first‐order static quadrupole effects on the NMR levels, are reported. Some data regarding the dc conductivity and the dielectric constant are mentioned and briefly discussed. Interesting insights in the static and dynamical properties of CsCuCI3, around the 418 K phase transition to the helical electric dipole structure driven by the cooperative Jahn‐Teller effect are obtained. The 133Cs spin‐lattice relaxation is driven by the fluctuations of the dipolar magnetic field from the Cu2+ ion and its temperature dependence is interpreted in the light of the properties of the electronic spin dynamics in presence of crystalline field effects.

Effects of different rare earths on the temperature dependence of rare earth cobalt magnets

In many applications, it is necessary to have permanent magnets whose characteristics vary little around a temperature T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> . We have developed a calculation to describe the thermal variation of the magnetization of the rare earth (RE) in such magnets including the effects of crystalline field. The exchange field of cobalt has been deduced at all temperatures from magnetization measurements on a single crystal of YCo <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> . From the calculation we can deduce the concentration x <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> , which gives dM/dT = 0 around room temperature, the resulting magnetization and the corresponding <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d^{2}M/dT^{2}</tex> .

X-ray Compton profile of lithium in low momentum transfer region

X-ray Compton profile of polycrystalline lithium was precisely measured at a scattering angle of 140 degrees for Cu K beta 1 radiation. The momentum transfer was relatively small (q=0.703 au) compared with usual Compton experiments. A double-crystal spectrometer was used and the resultant energy resolution was about 21 eV. The observed Compton profile was remarkably asymmetric. It was compared with a theoretical analysis which took into account the effects of crystalline field and electron correlation. The agreement between the theoretical curve and the experimental profile was fairly good. It is concluded that when the momentum transfer is not large enough, the Compton recoil conduction electrons are affected by the crystalline field, and the binding effect can not be neglected for the core electrons. Both electrons, therefore, can not be regarded as completely free and the Compton profile becomes asymmetric.