Crystal Electric Field Effects Research Articles

Local investigation of the crystal electric field ground-state in CeCu(Sb,Bi)$_2$ heavy fermions

In this work, we performed systematic Nuclear Magnetic Resonance (NMR) and magnetic susceptibility experiments in CeCuSb_22 single-crystals. The main findings were compared to previous report for CeCuBi_22. The NMR spectra and transferred hyperfine coupling for the ^{63}63Cu nuclei were obtained aiming to observe their correlation with the crystal electric field (CEF) effects on the Ce^{3+}3+ (J=5/2J=5/2) multiplet. Besides, in an attempt to elucidate the magnetic structure through NMR measurements at different magnetic fields orientations, we observed a magnetic transition at T\approx 8\,T≈8K higher than the Néel temperature T_NTN measured by magnetic susceptibility indicating the development of short-range magnetic ordering above T_NN. In addition, the wipe out of the main NMR resonance line and a persistent spin-echo signal throughout the whole frequency-swept range suggest the possibility of an incommensurate magnetic structure in CeCuSb_22. Furthermore, the small transferred hyperfine coupling constant found for CeCuSb_22 indicates a scenario with more localized Ce^{3+}3+ 4f electrons than for CeMIn_55 (M == Co,Rh,Ir) heavy fermions family. Additionally, subtle changes in the hybridization between the ^{63}63Cu with the 4f^11 Ce^{3+}3+ electrons in distinct magnetic field orientations allowed us to provide detailed information and map out the 4f CEF orbital ground-state of CeCu(Sb,Bi)_22 via NMR measurements.

Diffusive excitonic bands from frustrated triangular sublattice in a singlet-ground-state system

Magnetic order in most materials occurs when magnetic ions with finite moments arrange in a particular pattern below the ordering temperature. Intriguingly, if the crystal electric field (CEF) effect results in a spin-singlet ground state, a magnetic order can still occur due to the exchange interactions between neighboring ions admixing the excited CEF levels. The magnetic excitations in such a state are spin excitons generally dispersionless in reciprocal space. Here we use neutron scattering to study stoichiometric Ni2Mo3O8, where Ni2+ ions form a bipartite honeycomb lattice comprised of two triangular lattices, with ions subject to the tetrahedral and octahedral crystalline environment, respectively. We find that in both types of ions, the CEF excitations have nonmagnetic singlet ground states, yet the material has magnetic order. Furthermore, CEF spin excitons from the tetrahedral sites form a dispersive diffusive pattern around the Brillouin zone boundary, likely due to spin entanglement and geometric frustrations.

Random magnetic anisotropy in a new compound Sm2AgSi3

We report the experimental study on the structural and magnetic properties of a new ternary intermetallic compound Sm2AgSi3. The properties of the sample were investigated in detail by X-ray diffraction, dc–magnetization, and heat capacity measurements. The polycrystalline compound of Sm2AgSi3 crystallizes in the ThSi2-type tetragonal structure (space group I41/amd). The temperature dependent dc–magnetization and heat capacity results demonstrate that the compound undergoes ferromagnetic behaviour with a Curie temperature (TC) of 14 K. The large coercive field in hysteresis loops and the thermomagnetic irreversibility in the ferromagnetic region revealed that the compound exhibits a large magnetic anisotropy. The magnitude of the applied field and the coercivity obtained from the M-H loops corroborate with the thermomagnetic irreversibility in the magnetization data. The magnetic contribution of the heat capacity reveals a broad Schottky–type anomaly above TC, due to the presence of the crystal electric field effect of Sm3+ in Sm2AgSi3.

Investigation on thermal and electron transport properties combined with the low-temperature scaling behaviour of strongly correlated Ce2Rh3Al9

The paper presents some new aspects of the heat transport properties and thermoelectric characteristic of the heavy fermion Kondo lattice Ce2Rh3Al9. A thorough analysis of the obtained experimental data was presented along with their detailed discussion, paying particular attention to the range of low temperatures. The temperature dependence of thermoelectric power shows large values and reveals several well formed extrema, which reflect the crystal electric field effects and the Kondo scale, respectively. The giant positive slope of the Seebeck coefficient displayed in the form of the ratio S(T)/T is observed at low temperatures. Different to the thermoelectric power, the absolute values of thermal conductivity in Ce2Rh3Al9 are quite low. In addition, we have investigated the response of thermal and electron transport on the presence of a perpendicular static magnetic field of B = 9 T. For the sake of completeness, the field dependence of the transverse magnetoresistance data recorded between 0.4 ≤ T ≤ 20 K is presented and discussed as well.

Unconventional magnetic order emerging from competing energy scales in the new RRh3Si7 intermetallics ( R = Gd-Yb)

The competition between Ruderman-Kittel-Kasuya-Yosida (RKKY), crystal electric field (CEF), and Kondo energy scales has recently emerged at the heart of complex magnetism in several Ce- or Yb-based intermetallics. Hard axis magnetic order has been observed in a handful of these compounds, independent of the crystal symmetry, size of the ordered moment, or the relative scale of the Kondo and magnetic ordering temperatures. This raises the question of the role of each energy scale in driving the ground state properties. In focusing on a single class of compounds, the rhombohedral R${\mathrm{Rh}}_{3}{\mathrm{Si}}_{7}$, we compare the anisotropy and magnetic ground states in members of this series with only RKKY interactions (R = Gd), or RKKY and CEF effects (R = Tb-Tm), with the behavior of the R = Yb compound, where all three energy scales (RKKY, CEF, Kondo) are at play. Moreover, we extend the comparison to two other isostructural Kondo systems ${\mathrm{YbIr}}_{3}{\mathrm{Si}}_{7}$ and ${\mathrm{YbIr}}_{3}{\mathrm{Ge}}_{7}$, where hard axis magnetic order is also observed. The non-Kondo compounds R${\mathrm{Rh}}_{3}{\mathrm{Si}}_{7}$ (R = Tb-Tm) lack the complexity of magnetic order along the hard CEF axis, pointing to the dominant role of the Kondo effect in driving this magnetic order. However, the CEF-RKKY competition is still responsible for complex magnetic ground states, and it appears that the electronic and magnetic degrees of freedom are entangled in all magnetic members of this series of compounds.

A new look at the ground state properties of Ce2Ir3Al9: Coexistence of two competing energy scales

We present an extended research on characterization of the ground state in a polycrystalline compound Ce2Ir3Al9 using powder x-ray diffraction, magnetic susceptibility χ(T), isothermal magnetization M(B), specific heat Cp(T), electrical resistivity ρ(T), magnetoresistivity ρ(B), thermoelectric power S(T) and thermal conductivity κ(T) measurements, together with a theoretical description of the obtained data to develop a more profound understanding of the physics in this compound. Ce2Ir3Al9 crystallizes in the orthorhombic Y2Co3Ga9-type of structure (space group Cmcm, No. 63, oC56, Z = 4). The χ(T) and Cp(T)/T data reveal the signatures of intermediate valence behaviour on Ce ions with the approximate value of the Kondo temperature TK = 96 K and the Sommerfeld coefficient γ = 31 mJ/mol ⋅ K2. In contrast to the magnetometric and thermodynamic measurements, the transport data (ρ(T) and S(T)) indicate the development of the Kondo lattice state. Accordingly, we expect that for Ce2Ir3Al9 the most likely scenario, which develops in a wide T range is the coexistence and competition of two energy scales of interactions between conduction electrons and 4f spins on Ce ions, located in one unique crystallographic site in the unit cell, in consequence carrying out our system from Ce4+Temp.→ Ce3+. At higher temperatures, where the Kondo interaction becomes dominant the influence of the crystal electric field effect seems to play an influential role in the ground state of this compound too.

Rare-earth pyrocoboltates [formula omitted]Co2O7 (R = Ce, Yb): Effective spin-[formula omitted] antiferromagnetic insulators with strong geometrical frustration

The two new rare-earth pyrocoboltates R2Co2O7 (R = Ce, Yb) adopt the layered monoclinic Ca2Nb2O7-type structure with the space group P21(No. 4). Both compounds have been investigated by DC magnetic susceptibility χdc(T), AC magnetic susceptibility χac(T) and isothermal magnetization M(B) measurements. The observed effective magnetic moment of Ce2Co2O7 indicates a contribution from the Co sublattice while that of Yb2Co2O7 is mainly from the localized 4f13 electronic configuration of Yb3+ ion. A magnetic ordering of the antiferromagnetic-type is observed in Ce2Co2O7 at TN≃ 34 K. This ordering is accompanied by the opening of a magnetic spectral gap, Δ=57.7 K (~ 5.0 meV) in the spin-wave spectrum and it survives in an external magnetic field of 7 T. In addition to the transition at TN,χac(T) measurements reveal a dome-like feature centered at ≃ 20 K in high frequency which indicates the presence of possible short-range correlation. In Yb2Co2O7, a magnetic phase transition is observed below TN=2.94 K, which is suppressed below 1.9 K in an external magnetic field of 3 T. In the low-T region where the crystal electric field effects can be neglected, an effective spin-1/2 state is realized in Yb2Co2O7, with a Landé-g factor of 3.76 which is comparable to values observed from electron spin resonance (ESR) measurements on related systems. In addition, M(B) of Yb2Co2O7 shows a metamagnetic-like feature at a critical field of HC≈2.5 T. Signatures from both compounds reveal the presence of strong magnetic frustrations with frustration index f of 9.17 and 15.12 for Ce2Co2O7 and Yb2Co2O7, respectively.

Intrinsic Bulk Quantum Oscillations in a Bulk Unconventional Insulator SmB6.

SummaryThe finding of bulk quantum oscillations in the Kondo insulator SmB6 proved a considerable surprise. Subsequent measurements of bulk quantum oscillations in other correlated insulators including YbB12 lent support to our discovery of a class of bulk unconventional insulators that host bulk quantum oscillations. Here we perform a series of experiments to examine evidence for the intrinsic character of bulk quantum oscillations in floating zone-grown single crystals of SmB6 that have been the subject of our quantum oscillation studies. We present results of thermodynamic, transport, and composition analysis experiments on pristine floating zone-grown single crystals of SmB6 and compare quantum oscillations with metallic LaB6 and elemental aluminum. These results establish the intrinsic origin of quantum oscillations from the insulating bulk of floating zone-grown SmB6. The similarity of the Fermi surface in insulating SmB6 with the conduction-electron Fermi surface in metallic hexaborides is at the heart of a theoretical mystery.

Crystal electric field effects and heavy-fermion behavior in cubic PrCu2Au3 compound

We report the crystal structure as well as the magnetic, electronic and transport properties of PrCu2Au3 which crystallizes in the MgCu4Sn-type structure with the cubic space group F4¯3m (No. 216). In this structure, the Pr3+ ion sits on a lattice site with the cubic Td symmetry which dictates the crystal electric field (CEF) splitting of the Hund’s 3H4 ground multiplet into four levels. The sample has been investigated by measurements of temperature dependences of specific heat, Cp(T), electrical resistivity, ρ(T), magnetic susceptibility, χ(T), isothermal magnetization, M(B,T), thermal conductivity, κT(T) and thermoelectric power, S(T). χ(T) follows a Curie-Weiss behavior above 100 K with an effective magnetic moment, μeff = 3.3 μB/Pr which is comparable to a calculated value of 3.58 μB/Pr for a free Pr3+ ion and a Weiss temperature, θCW = 15.70 K indicating a dominant ferromagnetic interaction. From the analysis of M(B,T) and the 4f-electron derived specific heat (C4f(T)) results, the CEF ground state is a Γ5 magnetic triplet and the CEF energy scheme is presented. The Sommerfeld coefficient, γ estimated from the low-temperature C4f(T) is 304 mJ/(mol K2) indicating a mass enhancement of the conduction electrons at low temperatures. Further analysis of the heavy fermion properties based on the Sommerfeld-Wilson ratio supports the formation of a heavy fermion state in PrCu2Au3. However, the absence of an enhancement in S/T at low temperatures possibly suggests a weak correlation between the conduction electrons and the 4f-electrons at the Fermi energy. The thermal transport properties suggest that PrCu2Au3 is likely a compensated metal.

Дослідження впливу концентрації рідкокристалічної присадки та електричного поля на фізико-хімічні властивості індустріальної оливи

Мета: Метою статті є вивчення впливу концентрації рідкокристалічної присадки та електричного поля на в’язкість індустріальної оливи, а також дослідження впливу концентрації на низькотемпературні властивості оливи. Методи: Дослідження і розрахунки проводилися за методами описаними в державних стандартах ДСТУ ГОСТ 33-2003, ГОСТ 25371-2018 та ГОСТ 20287-91. Результати: Отримано залежність зміни в’язкості та температури застигання індустріальної оливи від концентрації рідкокристалічної присадки. Отримано залежність зміни в’язкості індустріальної оливи при обробці електричним полем, за різних концентрацій рідкокристалічної присадки. Розраховано індекс в’язкості для індустріальної оливи з різними концентраціями присадки. Обґрунтовано обраний нами діапазон концентрацій. Результати досліджень оброблені в програмі Statistica, отримано рівняння регресії, які описують залежність в’язкості оливи від концентрації присадки.

Synthesis, magnetization, and heat capacity of triangular lattice materials NaErSe2 and KErSe2

In this paper we report the synthesis, magnetization and heat capacity of the frustrated magnets \emph{A}ErSe$_2$(\emph{A}=Na,K) which contain perfect triangular lattices of Er$^{3+}$. The magnetization data suggests no long-range magnetic order exists in \emph{A}ErSe$_2$(\emph{A}=Na,K), which is consistent with the heat capacity measurements. Large anisotropy is observed between the magnetization within the \emph{ab} plane and along the \emph{c} axis of both compounds. When the magnetic field is applied along \emph{ab} plane, anomalies are observed at 1.8 $\mu_B$ in NaErSe$_2$ at 0.2 T and 2.1 $\mu_B$ in KErSe$_2$ at 0.18 T. Unlike NaErSe$_2$, a plateau-like field-induced metamagnetic transition is observed for H$\|$\emph{c} below 1 K in KErSe$_2$. Two broad peaks are observed in the heat capacity below 10 K indicating possible crystal electric field(CEF) effects and magnetic entropy released under different magnetic fields. All results indicate that \emph{A}ErSe$_2$ are strongly anisotropic, frustrated magnets with field-induced transition at low temperature. The lack of signatures for long-range magnetic order implies that these materials are candidates for hosting a quantum spin liquid ground state.

Antiferromagnetic ordering and Kondo lattice behavior in moderate heavy fermion system Ce3NiSi3

Abstract We report the low temperature physical properties of polycrystalline R3NiSi3 (R = La and Ce) which crystallizes in orthorhombic (Space group Immm) structure. The results of our comprehensive study by means of magnetic, electrical transport and thermodynamic measurements suggest that Ce3NiSi3 orders antiferromagnetically below T N ∼ 6 K. Electrical resistivity and magnetoresistance data of Ce3NiSi3 resembles with that observed in usual Ce based Kondo lattice/heavy fermion (HF) compounds. Electrical resistivity and heat capacity are significantly influenced by the crystal electric field (CEF) effect. An enhanced value of Sommerfeld coefficient (∼118.5 mJ/mol K2) strongly indicates HF behavior of Ce3NiSi3.

Magnetic phase diagram and crystal-field effects in the kagome-lattice antiferromagnet U3Ru4Al12

We report on the magnetic phase diagram of the distorted kagome-lattice antiferromagnet ${\mathrm{U}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Al}}_{12}$ determined through measurements of magnetic and elastic properties. For field applied along the [100] and [120] axes of the hexagonal crystal structure, we find pronounced anomalies in the magnetization and elastic moduli that signal the existence of unknown magnetic phases. Our crystal-electric-field (CEF) analysis evidences interlevel quadrupolar interactions between the ground-state singlet and the first excited doublet. These interactions lead to a large softening of the shear elastic modulus ${C}_{44}$. The large number of phases and pronounced elastic softening suggest that geometric frustrations and CEF effects play an important role in the physical properties of ${\mathrm{U}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Al}}_{12}$.

Change of electronic state in the noncentrosymmetric superconductor Th7Fe3

57Fe Mössbauer spectroscopy and specific heat measurements were performed for the noncentrosymmetric superconductor Th7Fe3. An explicit increase in the center shift δCS(T), normalised spectral area A(T)/A(1.5 K) and electric quadrupole splitting ΔEQ(T) is observed below 60 K. The temperature dependencies of δCS(T) and A(T)/A(1.5 K) follow the Debye model for , whereas ΔEQ(T) can be described by an empirical T3/2 equation in both two temperature ranges 2 K–T* and T*–300 K. The behaviour of ΔEQ(T) can more willingly be interpreted in terms of the Fe3+ charge distributions on the singlet (dxy) ground state, the doublet (dxz, dzy) of T2g and doublet () of Eg excited states, characterised by respective splitting energies Δ1 and Δ2. It is shown that the excited energies deduced from the 57Fe Mössbauer data are in good agreement with those of Schottky specific heat. We argue that the anomaly detected in hyperfine parameters and specific heat substantially associates with change in the electronic state of the Fe atoms. We are convinced that a precursor crystal-electric field (CEF) effect has undergone before the onset of superconductivity sets in at lower temperature and the present results would spur new interest to researchers about the interplay between CEF and superconductivity in noncentrosymmetric materials.

Magnetic-field-induced quadrupolar ordering and the crystal electric field effect in the distorted kagome lattice antiferromagnet Dy3Ru4Al12

To investigate the $4f$-electronic states under a crystal electric field (CEF) and the phase transition in ${\mathrm{Dy}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Al}}_{12}$ with the antiferromagnetic transition temperature ${T}_{\mathrm{N}}=7$ K, we performed ultrasonic measurements on a single-crystalline sample at zero magnetic field and under fields. The transverse elastic modulus ${C}_{44}$ shows a characteristic elastic softening. The CEF analyses indicate that the softening is caused by an interlevel quadrupole interaction between the ground and excited Kramers doublets. Under fields, we found a magnetic-field-induced phase transition along both the [100] and [001] directions in addition to the antiferromagnetic ordering. A plausible origin of the field-induced transition is quadrupolar ordering, which is estimated from our CEF calculation. These results and the negative sign of a quadrupole-quadrupole coupling constant suggest that the effect of geometrical frustration alignment due to the kagome lattice also appears on the electric quadrupoles of the Dy ions with the antiferroquadrupolar-type interaction.

Sm valence states and magnetic properties in SmBe13 and SmTi2Al20 investigated by Sm synchrotron-radiation-based Mössbauer spectroscopy

Synchrotron-Radiation-based \(^{\mathrm {149}}\)Sm Mossbauer spectroscopy was applied to Sm intermetallics, SmBe13 and SmTi2Al20. Temperature dependence of the Mossbauer parameters in SmBe13 indicate the Sm valence state is purely trivalent. SmBe13 also showed second-order Doppler shift in synchrotron-radiation-based \(^{\mathrm {149}}\)Sm Mossbauer spectroscopy. The Mossbauer parameters obtained in SmTi2Al20 suggest that the Sm valence is fluctuating and the magnitude of the magnetic moment is reduced by hybridization between 4f and conduction electrons and/or effect of crystal electric field.

Elastic moduli of the distorted Kagome-lattice ferromagnet Nd3Ru4Al12

The distorted kagome-lattice compound Nd3Ru4Al12 has the hexagonal structure. This compound is reported as a ferromagnet in which spins are aligned along the c-axis with the Curie temperature TC=39K. The nature of localized f-electrons is expected in Nd3Ru4Al12, and magnetic anisotropy can be attributed to a crystal electric field (CEF) effect. We performed ultrasonic measurements on a Nd3Ru4Al12 single-crystalline sample in order to investigate the phase transition at TC and the CEF effect. All longitudinal and transverse elastic moduli increase monotonically with decreasing temperature, and no clear elastic softening due to a quadrupole interaction is detected under the hexagonal CEF. This result is in contrast to an isomorphic compound Dy3Ru4Al12 with a remarkable elastic softening of the transverse modulus C44. At the ferromagnetic phase transition, the moduli show obvious elastic anomalies, suggesting characteristic couplings between a strain and a magnetic order parameter.

Low-temperature transport and thermodynamic properties of dense Kondo alloys [formula omitted

The alloys Ce8Pd24(Al1−xSnx) with 0≤x≤1 were studied by means of electrical resistivity, thermal conductivity, thermoelectric power, magnetic susceptibility and magnetization measurements. In the entire composition range, an antiferromagnetic (AFM) long-range ordering has been established at low temperatures, with the Néel temperature increasing linearly from TN = 4.3 K for Ce8Pd24Al to TN = 7 K for Ce8Pd24Sn. Below TN, the electrical resistivity is dominated by scattering conduction electrons on spin-wave excitations. In the paramagnetic state, the electrical transport in the alloys with 0≤x≤0.7 reveals both coherent Kondo lattice scattering and crystal-electric field (CEF) effect, while that in the alloys with x≥0.8 appears governed by CEF only. Above TN, all the alloys exhibit well localized magnetic behavior due to trivalent Ce ions. At high temperatures, the thermoelectric power can be interpreted in terms of a phenomenological resonance model giving an estimate of the CEF effect. The thermoelectric figure of merit of Al-rich alloys is small compared to those of commercial thermoelectric materials.

Defect mode and crystal-electric-field effects on the thermal expansion and heat capacity of RB50 boride

Specific heat and thermal expansion in LuB50 and TbB50 borides at 2–300 K were experimentally studied. In both compounds, for a large range of low temperatures a negative thermal expansion caused by defects in the crystal lattice was observed. The effect of the crystal electric field on the thermal characteristics of TbB50 was observed as a Schottky anomaly in the temperature dependence of the heat capacity and as an additional negative contribution to the thermal expansion. The analysis of the heat capacity data suggests that the ground state of the ion Tb3+ is a quasi-quintet, consisting of close-located singlet and two doublets. The phase transition of TbB50 to the antiferromagnetic state appears as a very weak broad anomaly in the temperature dependence of the heat capacity; within the scattering of the experimental data, it is not visible in the temperature dependence of the unit cell volume.

Ultrasonic Study on the Hexagonal Antiferromagnet Dy3Ru4Al12

In the distorted kagome lattice antiferromagnet Dy3Ru4Al12 with TN = 7 K, a crystal electric field (CEF) effect is expected at high temperatures. To investigate the CEF effect and the phase transition at TN, we performed ultrasonic measurements on a single-crystalline sample. At high temperatures, both the longitudinal elastic modulus C11 and the transverse modulus C44 increase monotonically with decreasing temperature. Below 60 K a characteristic elastic softening is observed in C44 in contrast to C11 with monotonic hardening down to TN. We analyzed C44 using the Curie-Weiss-type equation and obtained a negative parameter: Θ which is proportional to a quadrupole-quadrupole coupling constant under the hexagonal CEF. With further decreasing temperature, both moduli exhibit abrupt elastic hardening at TN due to a magnetostriction.