Crystalline Electric Field Effects Research Articles

Crystalline electric field and large anomalous Hall effect in NdGaGe single crystals

We grew NdGaGe single crystals and investigated their magnetic and electrical transport properties. The magnetic susceptibility data revealed that NdGaGe orders magnetically at Tm≈ 8.8 K; also confirmed by heat capacity and electrical resistivity data. In ordered state, the heat capacity and electrical resistivity data exhibit a gapped-magnon behavior with an energy gap of ∼ 4.7 K. Our detailed crystalline electric field analysis of magnetic susceptibility, magnetization, and heat capacity data indicates that the (2J+1) degenerate energy levels of Nd3+ ion split into five doublets with an overall splitting of ∼ 123 K. We observe a large anomalous Hall conductivity (AHC) ∼530Ω−1 cm−1 at 2 K, which is close to the theoretical expected value due to intrinsic Berry-curvature. Moreover, the scaling parameter between anomalous Hall resistivity and magnetoresistivity together with the linear relationship between AHC and saturation magnetization suggests that the origin of large AHC in NdGaGe is due to the intrinsic Berry curvature.

Y-Substitution effects in the crystal field of the trigonal YxRE1−xNi3Ga9 (RE = Tb, Dy, and Ho)

Multipolar ordering arising from the interplay between crystalline electric field (CEF) effects and magnetic interactions has been gaining more attention in 4f systems. In this work, we explore this possibility in the chiral magnets RENi3Ga9 (RE = Tb, Dy and Ho; x = 0.15 and 0.30) through Y-dilution. We present temperature-dependence of the M∕H curves, isothermal magnetization and heat-capacity experiments. Single crystalline samples grown by Ga self flux allow us to measure the magnetic properties for different crystallographic directions. X-ray diffraction patterns analyzed by Rietveld method indicate that all samples crystallize in a trigonal ErNi3Al9-type structure with space group R32. Our results are consistent with an antiferromagnetic order with transition temperatures TN< 20 K for all the studied samples, which decrease gradually with Y-substitution. By using a mean field model including anisotropic near- and next-near-neighbors magnetic interactions and the trigonal CEF Hamiltonian, we are able to study in detail the evolution of the crystal-field scheme and magnetic couplings for these compounds. We show that the spatial charge distribution between the compounds are in agreement, increasing the confidence of the obtained CEF schemes. Finally, we compare our fittings with disorder simulations assuming that CEF effects should not evolve as a function of Y-substitution. Our results show that only disorder effects do not fully describe the experimental data, which may indicate that quadrupolar degrees of freedom indeed have a role in the magnetic properties of this family.

Antiferromagnetism of CeCd0.67As2 existing deep inside the narrow gap semiconducting state

Single crystals of $R$Cd$_{0.67}$As$_2$ ($R$ = La and Ce) have been synthesized by high temperature ternary melt and their physical properties have been explored by means of magnetization, specific heat, electrical resistivity, Hall coefficient, and thermoelectric power measurements. $R$Cd$_{0.67}$As$_2$ compounds indicate a (structural) phase transition at high temperatures, accompanied by a remarkable increase of the electrical resistivity with an extremely low carrier concentration. CeCd$_{0.67}$As$_2$ exhibits a large magnetic anisotropy and an antiferromagnetic (AFM) order below $T_{N} = 4$~K. Magnetic susceptibility curves, together with magnetization isotherms and specific heat, are analyzed by the point charge model of crystalline electric field (CEF). In the paramagnetic state, the observed magnetic properties can be well explained by the CEF effects, implying that the 4$f$ moments remain localized. Electrical resistivity measurements, together with Hall resistivity and thermoelectric power, also suggest highly localized 4$f$ electrons, where Kondo contributions are negligible. The low temperature physical properties manifest strong magnetic field dependencies. For $H \perp c$, $T_{N}$ shifts to lower temperature as magnetic field increases, and eventually disappears at $H_{c} \sim 60$~ kOe. Inside the AFM state, three metamagnetic transitions are clearly evidenced from the magnetization isotherms. The RKKY interaction may be responsible for the AFM ordering in CeCd$_{0.67}$As$_2$, however it would have to be mediated by extremely low charge carriers. Although the AFM ordering temperature in CeCd$_{0.67}$As$_2$ can be continuously suppressed to zero, no AFM quantum phase transition is expected due to the lack of conduction electron clouds to screen the 4$f$ moments.

Heterometallic Gd-Dy Formate Frameworks for Enhanced Magnetocaloric Properties.

Lanthanide-based metal-organic frameworks (MOFs) have great potential as magnetic refrigerants under cryogenic conditions and are comparable to conventional alloys and magnetic nanoparticles. In particular, MOFs with Gd3+ ions behave as excellent magnetic refrigerants because of their large spin ground states. However, the major drawback of Gd3+-based MOFs is that they are not affected by the ligand material owing to the excessively large spin-only magnetic moment; therefore, their application is limited to the cryogenic region in the magnetic cooling field. In this study, we report the magnetic properties and magnetocaloric effect (MCE) resulting from heterogenized MOFs obtained from the reaction of Gd3+ and Dy3+ ions and their varied molar composition with the formate ligand. For GdxDy1-x-(HCOO)3, where 0 ≤ x ≤ 1, the isothermal magnetic entropy change (ΔSm) increased with the increase in the fraction of Gd in the heterogenized MOFs. Meanwhile, with increasing Dy contents, the maximum peak temperature of ΔSm is shifted to a higher temperature while preserving a relatively high ΔSm value of 22.35 J·kg-1 K-1 at T = 7 K for an applied field change (ΔH) of 7 T despite the anisotropy and crystalline electric field effects. Furthermore, it was confirmed that the samples with a Dy content of 75% or more maintained the ΔSm operating temperature longer. Therefore, the current approach of including Dy3+ ions in lanthanide compounds provides the possibility of further extending the operating temperature of magnetic cooling materials from cryogenic temperatures.

Anisotropic magnetic property of single crystals RV6Sn6 (R=Y, Gd−Tm, Lu)

$R$V${_6}$Sn${_6}$ ($R$ = Y, Gd - Tm, Lu) single crystals are synthesized by Sn-flux method and their physical properties are characterized by magnetization, resistivity, and specific heat measurements. Powder X-ray diffraction patterns of all samples can be well indexed with the hexagonal HfFe$_6$Ge$_6$-type structure, where rare-earth atoms form hexagonal layers and vanadium atoms form Kagome layers. At high temperatures, magnetic susceptibility measurements of moment bearing rare-earths ($R$ = Gd - Tm) follow Curie-Weiss behavior. Effective moments estimated from the polycrystalline average of magnetic susceptibility curves are consistent with the values for free $R^{3+}$ ion. Strong magnetic anisotropy due to crystalline electric field effects is observed for moment bearing rare-earths, except GdV$_6$Sn$_6$. The easy magnetization direction is determined to be $c$-axis for $R$ = Tb - Ho and $ab$-plane for $R$ = Er, and Tm. The vanadium ions in $R$V${_6}$Sn${_6}$ possess no magnetic moment. The compounds for $R$ = Y and Lu exhibit typical characteristics of paramagnetic metals. At low temperatures, the magnetic ordering is confirmed from magnetization, specific heat, and resistivity: the highest $T_{N} = 4.9$~K for GdV$_6$Sn$_6$ and the lowest $T_{N} = 2.3$~K for HoV$_6$Sn$_6$. No magnetic ordering is observed down to 1.8~K for $R$ = Er and Tm. A slight deviation of the magnetic ordering temperature from the de Gennes scaling suggests the dominant Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction between rare-earth moments in metallic $R$V${_6}$Sn${_6}$ compounds.

Zigzag magnetic order in a novel tellurate compound Na4−δNiTeO6 with S = 1 chains

Na4−δNiTeO6 is a rare example in the transition-metal tellurate family of realizing an S = 1 spin-chain structure. By performing neutron powder diffraction measurements, the ground-state magnetic structure of Na4−δNiTeO6 is determined. These measurements reveal that below TN ∼ 6.8(2) K, the Ni2+ moments form a screwed ferromagnetic (FM) spin-chain structure running along the crystallographic a axis but these FM spin chains are coupled antiferromagnetically along the b and c directions, giving rise to a magnetic propagation vector of k = (0, 1/2, 1/2). This zigzag magnetic order is well supported by first-principles calculations. The moment size of Ni2+ spins is determined to be 2.1(1)μB at 3 K, suggesting a significant quenching of the orbital moment due to the crystalline electric field (CEF) effect. The previously reported metamagnetic transition near HC ∼ 0.1 T can be understood as a field-induced spin-flip transition. The relatively easy tunability of the dimensionality of its magnetism by external parameters makes Na4−δNiTeO6 a promising candidate for further exploring various types of novel spin-chain physics.

Ce site dilution effects in the antiferromagnetic heavy fermion CeIn3

La-doped intermetallic single crystals of ${{\mathrm{Ce}}_{1}}_{\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{In}}_{3}$ were synthesized via an In self-flux method throughout the entire range $(x=0--1)$. The prototypical heavy-fermion compound ${\mathrm{CeIn}}_{3}$ shows an antiferromagnetic phase transition at 10.1 K and becomes superconducting near a critical pressure where ${T}_{N}$ is completely suppressed. As the La concentration increases, Ce moments are diluted, and the lattice constant increases linearly, satisfying Vegard's law. The electrical resistivity of the high-quality single crystals of ${{\mathrm{Ce}}_{1}}_{\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{In}}_{3}$ shows a gradual suppression of ${T}_{N}$ to 0 K at approximately ${x}_{c}=0.65$. The sign of the slope of the low-temperature resistivity vs temperature changes from positive to negative in the vicinity of the critical concentration ${x}_{c}$, indicating a change in the Kondo ground states from the Kondo lattice to the Kondo impurity state. In the Kondo lattice state $(x&lt;{x}_{c})$, the coherence temperature $(=50\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ assigned as the peak in the resistivity is almost independent of the La concentration. In the Kondo impurity state $(x&gt;{x}_{c})$, on the other hand, a kinklike feature in the resistivity appears at $\ensuremath{\sim}50\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and persists up to $x=0.97$, indicating a change of the Kondo scattering owing to the crystalline electric field effects. These results suggest that the critical concentration is closely connected to the emergence of the Kondo coherence state.

Physical properties of Ce3+xRu4Sn13−x single crystals

Single crystals of ${\mathrm{Ce}}_{3+x}{\mathrm{Ru}}_{4}{\mathrm{Sn}}_{13\ensuremath{-}x}$ $(0.05\ensuremath{\le}x\ensuremath{\le}0.34)$, which adopt the cubic structure ($Pm\overline{3}n$, No. 223), have been grown with Sn flux. Thermodynamic and transport property measurements from single-crystal samples do not show any sign of magnetic ordering down to 1.8 K and indicate coexistence of the Kondo effect and crystalline electric field effect. The local minimum in the electrical resistivity and highly enhanced specific heat values at low temperatures characterize this family as a heavy fermion Kondo lattice system. A broad peak is observed at $\ensuremath{\sim}$3.5 K for $x=0.05$ in the specific heat and magnetic susceptibility, suggesting a significant Kondo contribution, and the peak disappears as $x$ increases. The evolution of physical properties of ${\mathrm{Ce}}_{3+x}{\mathrm{Ru}}_{4}{\mathrm{Sn}}_{13\ensuremath{-}x}$ compounds can be attributed to the nature of the individual Ce ions that occupy two inequivalent $2a$ and $6d$ crystallographic sites.

Thermal Expansion in a diluted Ce system La1–x Ce x Cu6

The thermal expansion of a diluted Ce system La1-x Ce x Cu6 for (0.6 ≤ x ≤ 1) has been measured between 10 and 150 K to reveal the change from the coherent heavy Fermion state (0.9 ≤ x ≤ 1) to the incoherent Kondo state (0 < x ≤ 0.73). The large Ce concentration x dependence of the linear thermal expansion coefficient along b-axis αb (T) suggests that the coupling between the 4f 1 electron and the lattice strain is the largest along the b-axis in the three crystallographic axes. The maximum of the magnetic contribution to the volume thermal expansion coefficient β m(T) at T = 50 K is retained in the x range of 0.6 ≤ x ≤ 1, suggesting the crystalline electric field (CEF) level for x = 1 doesn’t change by the substitution. Furthermore, the upturn in β m(T) below 25 K, which should be a precursor of the maximum at T = 2.5 K reported for x = 1, is retained when we decrease x from 1 to 0.6. Because the ground state for x = 0.6 is the incoherent Kondo state, the robustness of the maximum at T = 50 K and upturn in the current x value implies that β m(T) in 10 ≤ T ≤ 150 K is attributed to the CEF and Kondo effects rather than the formation of the heavy Fermion state.

Anisotropic magnetism and antiferromagnetic ordering in the Kondo-lattice compound YbCuAs2

Single crystals of $R\mathrm{Cu}{\mathrm{As}}_{2}$ ($R=\mathrm{Yb}$ and Y) have been synthesized from high temperature ternary melts and their physical properties investigated by magnetization, electrical resistivity, specific heat, and $\ensuremath{\mu}\mathrm{SR}$ measurements. Magnetization measurements of $\mathrm{Yb}\mathrm{Cu}{\mathrm{As}}_{2}$ suggest that $4f$ electrons are almost localized and the observed magnetic properties are influenced by the Kondo and Ruderman-Kittel-Kasuya-Yosida interactions as well as crystalline electric field (CEF) effect. Electrical resistivity measurements show typical Kondo-lattice behavior with a broad local maximum around $\ensuremath{\sim}125\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and a secondary hump around $\ensuremath{\sim}20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, suggesting a strong hybridization between $4f$ and conduction electrons. A small residual resistivity $(\ensuremath{\sim}0.68\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm})$ and the large residual resistivity ratio ($\mathrm{RRR}\ensuremath{\sim}150$) indicate a high quality single crystal. An analysis of the specific heat data indicates that the ground state doublet is well separated from excited CEF levels. Although an earlier neutron scattering experiment on powdered $\mathrm{Yb}\mathrm{Cu}{\mathrm{As}}_{2}$ samples observed no magnetic Bragg peaks associated with magnetic ordering, thermodynamic and transport property measurements in this study clearly indicate antiferromagnetic ordering below ${T}_{N}=3.7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ which is also supported by a muon spin relaxation investigation of $\mathrm{Yb}\mathrm{Cu}{\mathrm{As}}_{2}$ single crystals. The Kondo temperature (${T}_{K}$) estimated from the magnetic entropy and magnetic susceptibility is in the range $5--7.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is of similar magnitude as ${T}_{N}$. Interestingly, magnetization, specific heat, and electrical resistivity measurements as a function of magnetic field show a hysteresis loop both below and above ${T}_{N}$.

Effective magnetic Hamiltonian at finite temperatures for rare-earth chalcogenides

Alkali metal rare-earth chalcogenide $ARECh2$ (A=alkali or monovalent metal, RE=rare earth, Ch=O, S, Se, Te), is a large family of quantum spin liquid (QSL) candidates we discovered recently. Unlike $YbMgGaO4$, most members in the family except for the oxide ones, have relatively small crystalline electric-field (CEF) excitation levels, particularly the first ones. This makes the conventional Curie-Weiss analysis at finite temperatures inapplicable and CEF excitations may play an essential role in understanding the low-energy spin physics. Here we considered an effective magnetic Hamiltonian incorporating CEF excitations and spin-spin interactions, to accurately describe thermodynamics in such a system. By taking $NaYbSe2$ as an example, we were able to analyze magnetic susceptibility, magnetization under pulsed high fields and heat capacity in a systematic and comprehensive way. The analysis allows us to produce accurate anisotropic exchange coupling energies and unambiguously determine a crossover temperature ($\sim$25 K in the case of $NaYbSe2$), below which CEF effects fade away and pure spin-spin interactions stand out. We further validated the effective picture by successfully explaining the anomalous temperature dependence of electron spin resonance (ESR) spectral width. The effective scenario in principle can be generalized to other rare-earth spin systems with small CEF excitations.

Crystalline electrical field effects on powdered [formula omitted] Cu4Al8 ([formula omitted] = Tb, Dy, Ho and Er) intermetallic compounds

In this work, structural and magnetic properties RE Cu4Al8 (RE = Tb, Dy, Ho and Er) family of compounds are reported. Measurements of X-ray diffraction, temperature (T) and magnetic field (H) dependencies of magnetization are presented for each compound. The analysis of X-ray diffraction patterns shows a small variation in a (8.705824–8.734991 Å) and c (5.123802–5.135258 Å) lattice parameters as a function of the rare earth. The T-dependent magnetic susceptibility reveals the Curie-Weiss-like behavior at high-T evolving to antiferromagnetic transitions at low-T (6 <TN< 28 K) for all studied materials. Measurements of magnetization as a function of magnetic field show field-induced transitions for RE = Dy, Ho and Er, which present larger magnetic moments, though no magnetic saturation is attained (4.4 <Mmax< 7.3 μB) for none of the studied compounds. This fact is an indicative of strong crystalline electrical field (CEF) effects. We have conducted a detailed analysis, based on a mean-field spin model, in order to determine the CEF parameters from the macroscopic data of the studied powdered samples. Finally, to show the reliability of our calculations, the obtained CEF energy levels and wave functions are compared with previous CEF studies in single crystalline samples of ErCu4Al8, including results obtained from inelastic neutron scattering data.

Evolution of the magnetic properties in the antiferromagnet Ce2RhIn8 simultaneously doped with Cd and Ir.

We report the evolution of the magnetic properties of single crystals. In particular, for () and (), we have solved the magnetic structure of these compounds using single-crystal neutron magnetic diffraction experiments. Taking the magnetic structure of the heavy-fermion antiferromagnet as a reference, we have identified no changes in the magnetic wave vector; however, the direction of the ordered Ce3+ moments rotates toward the plane, under the influence of both dopants. By constraining the analysis of the crystalline electric field (CEF) with the experimental ordered moment's direction and high-temperature magnetic-susceptibility data, we have used a mean-field model with tetragonal CEF and exchange interactions to gain insight into the CEF scheme and anisotropy of the CEF ground-state wave function when Cd and Ir are introduced into . Consistent with previous work, we find that Cd doping in tends to rotate the magnetic moment toward the plane and lower the energy of the CEF excited states' levels. Interestingly, the presence of Ir also rotates the magnetic moment towards the plane although its connection to the CEF overall splitting evolution for the y = 0 samples may not be straightforward. These findings may shed light on the origin of the disordered spin-glass phase on the Ir-rich side of the phase diagram and also indicate that the compounds may not follow exactly the same Rh-Ir CEF effects trend established for the compounds.

Crystal structure and magnetic properties of novel La(Ce, Pr)R’PbSi2S8 (R’ = Ce, Pr, Sm, Tb, Dy, Y, Ho and Er) compounds

The formation of the La2-xR’xPbSi2S8 (R’ ​= ​Ce, Pr, Sm, Tb, Dy, Y, Ho, Er), Ce2-xR’xPbSi2S8 (R’ ​= ​Pr, Sm, Tb, Dy, Y, Ho, Er), and Pr2-xR’xPbSi2S8 (R’ ​= ​Sm, Tb, Dy, Y, Ho, Er) (x ​= ​1.5, 1.0, 0.5) solid solutions was established. The crystal structures of LaR’PbSi2S8 (R ​= ​Ce, Sm, Tb, Dy, Y, Ho, Er), CeR’PbSi2S8 (R’ ​= ​Pr, Sm, Tb, Dy, Y, Ho, Er) and PrR’PbSi2S8 (R’ ​= ​Sm, Tb, Dy, Y, Ho, Er) (La2PbSi2S8 structure type, space group R3¯c, Pearson symbol hR78) were determined by means of single crystal X-ray diffraction. Rare-earth and lead atoms are located in split positions inside bi-capped trigonal prisms made by chalcogen atoms. The Si atoms are located in tetrahedra. The crystal structure of the La2PbSi2S8 type can be derived from the Eu3As2S8 type by random substitution of the Eu atoms by the R, R′, and Pb atoms at their 18e site. The magnetic properties of LaR’PbSi2S8 (R ​= ​Ce, Sm, Tb, Dy, Y, Ho, Er), CeR’PbSi2S8 (R’ ​= ​Pr, Sm, Tb, Dy, Y, Ho, Er) and PrR’PbSi2S8 (R’ ​= ​Sm, Tb, Dy, Y, Ho, Er) were studied in wide temperature and magnetic field strength ranges. All these materials but weakly diamagnetic LaYPbSi2S8 were characterized as Curie-Weiss paramagnets due to the magnetic moments carried on trivalent rare-earth ions. At low temperatures, each compound exhibits distinct crystalline electric field effect, while in none of them any magnetic ordering emerges down to 1.72 ​K.

Magnetic and transport properties of low-carrier-density Kondo semimetal CeSbTe

Single crystals of CeSbTe with a ZrSiS-type structure were synthesized using vapor transport method. The stoichiometry is deviated from the nominal composition, which may cause some disorder in this compound. The physical properties were characterized by measuring the magnetic susceptibility, electrical resistivity, Hall resistivity and specific heat. One antiferromagnetic (AFM) transition related to Ce3+ ions was found at K, and a field-induced metamagnetic transition was observed below . The moderately enhanced Sommerfeld coefficient mJ mol−1 · K−2 and the estimated Kondo temperature K, indicate that CeSbTe is a moderately correlated AFM Kondo lattice compound with crystalline electric field effect. The carrier concentration of CeSbTe derived from the Hall coefficient is in the order of 1021 cm−3, lower than most Kondo metals, which indicates that CeSbTe is a low-carrier-density Kondo semimetal.

Realization of Kondo chain in CeCo2Ga8

We revisited the anisotropy of the heavy-fermion material CeCo$_2$Ga$_8$ by measuring the electrical resistivity and magnetic susceptibility along all the principal $\mathbf{a}$-, $\mathbf{b}$- and $\mathbf{c}$-axes. Resistivity along $\mathbf{c}$-axis ($\rho_c$) shows clear Kondo coherence below about 17 K, while both $\rho_{a}$ and $\rho_{b}$ remain incoherent down to 2 K. The magnetic anisotropy is well understood within the theoretical frame of crystalline electric field effect in combination with magnetic exchange interactions. We found the anisotropy ratio of these magnetic exchange interactions, $|J_{ex}^c/J_{ex}^{a,b}|$, reaches a large value of 4-5. We, therefore, firmly demonstrate that CeCo$_2$Ga$_8$ is a quasi-one-dimensional heavy-fermion compound both electrically and magnetically, and thus provide a realistic example of \textit{Kondo chain}.

Specific heat of Gd1−xErxGe1.5 as low-temperature-cryocooler regenerator materials

The specific heat C and the magnetization of Gd1−xErxGe1.5 were studied. From magnetization measurements, GdGe1.5 and ErGe1.5 showed antiferromagnetic ordering at the Néel temperatures TN of 29 K and 3 K, respectively. The jump in the C of Gd1−xErxGe1.5 due to the antiferromagnetic transition became small with increasing Er content, which is originated from the crystalline electric field effect and atomic randomness. Plots of C as a function of temperature for Gd1−xErxGe1.5 with x ≥ 0.5 exhibited a peak at temperatures below 15 K. These results suggest that TN could be controlled by substituting Er for Gd.

Crystal growth and magnetic characterization of HoIr2Si2 (I4/mmm)

Single crystals of HoIr2Si2 with the body-centered ThCr2Si2-type structure (I4/mmm) were grown by Bridgman method from indium flux. Single crystal structure determination yielded a Si-z position of 0.378(1) in the structure. We excluded the presence of the high temperature phase with the primitive CaBe2Ge2-type structure (P4/nmm) by powder x-ray diffraction. Magnetic measurements on the single crystals yield a Néel temperature of K. In the inverse magnetic susceptibility a strong anisotropy with Weiss temperatures K and K occurs above TN. The effective magnetic moment and is close to the expected value for a free Ho3+ ion, . The field dependent magnetization shows a step-like behaviour due to crystalline electric field effects. The temperature and field dependence of the magnetization hint to the ordering of the magnetic moments along the c direction below TN.

Effect of composition changes on the structural, magnetic and thermodynamic properties in Tb1-xDyxNi2 intermetallic compounds

The crystal structure, magnetic and thermodynamic properties of polycrystalline Tb1-xDyxNi2 intermetallic compounds with x = 0.25, 0.5 and 0.75 have been investigated. Experimental data on thermodynamic properties, i.e. the isothermal entropy change ΔSmag, are compared with results of theoretical calculations which were performed considering a model Hamiltonian that includes the crystalline electric field effects and exchange magnetic interaction.High-field isothermal magnetic entropy change was calculated according to magnetic measurements using thermodynamic Maxwell's relation. A large entropy change has been observed for all Dy concentrations. The maximum relative cooling power (RCP) of studied compounds reaches fairly high values, which are close to those reported for other magnetic refrigerants operating at temperatures below 40 K. The obtained results show that studied compounds can be considered as cooling agents in magnetic refrigerators performing an Ericsson cycle in the temperature range 20–40 K.

Electrical transport, magnetic, and thermodynamic properties of La-, Pr-, and Nd-doped BaSnO3−δ single crystals

Due to outstanding room temperature electron mobility, the wide-gap perovskite semiconductor $\mathrm{BaSn}{\mathrm{O}}_{3}$ is of high current interest. Although $n$ doping with Sb and O vacancies has been reported, most work has focused solely on La doping. Here we report bulk single crystals of $\mathrm{B}{\mathrm{a}}_{1\ensuremath{-}x}{R}_{x}\mathrm{Sn}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ with $R=\mathrm{La},\phantom{\rule{0.16em}{0ex}}\mathrm{Pr}$, and Nd, as well as unintentionally doped $\mathrm{BaSn}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$, thus exploring new rare earth (magnetic) dopants in addition to O vacancy doping. Consistent with recent results on epitaxial films, O vacancies are shown capable of generating mid-${10}^{19}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$ Hall electron densities, with single crystal mobilities $\ensuremath{\sim}100\text{--}150\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. Despite apparent solubility limits below $\ensuremath{\sim}0.5\phantom{\rule{0.16em}{0ex}}\mathrm{at}.\phantom{\rule{0.16em}{0ex}}%$, Pr and Nd are also shown to be effective $n$ dopants, yielding Hall electron densities $g1\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$, and ambient and low temperature mobilities up to 175 and $430\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, respectively. In contrast to the La-doped case, clear paramagnetism occurs with Pr and Nd doping, allowing for direct estimates of dopant concentrations for quantitative comparison with Hall densities. We show that dopant and Hall densities can be approximately reconciled, but only after accounting for O vacancy doping. Specific heat measurements were also performed, confirming the $\mathrm{BaSn}{\mathrm{O}}_{3}$ Debye temperature, and revealing electronic contributions roughly consistent with reported effective masses. Interestingly, and likely related to crystalline electric field effects, Pr-doped $\mathrm{BaSn}{\mathrm{O}}_{3}$ exhibits large deviations from simple Curie-Weiss susceptibility, and a pronounced Schottky anomaly, which we analyze in detail. These results provide significant insight into doping in $\mathrm{BaSn}{\mathrm{O}}_{3}$, establishing new rare earth magnetic dopants, clarifying the role of O vacancies, and determining dopant concentrations and solubility limits.