Curie-Weiss Temperature Research Articles

Magnetic and dielectric properties of the Co-defective Ca3Co2-xO6 compounds

The Ca3Co2-xO6 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) samples were prepared by reducing the stoichiometric ratio of Co atoms. Their structure, magnetic properties, dielectric and magnetodielectric properties were investigated. XRD results show that the presence of a small number of vacancies does not change the crystalline structure. The positive Curie-Weiss temperature θ and interchain exchange constants J indicate that ferromagnetic interactions are stronger than the antiferromagnetic interactions in Co-defective Ca3Co2-xO6. The Co-vacancies could weaken the Co-Co exchange interactions, it has an obvious dilution effect on the ferromagnetic interactions within the chain. The magnetization steps move to low field accompanying the defects increase. Simultaneously, Co defects could also release part of the magnetic frustration. The competition of the released magnetic frustration and the dilution effect of the vacancies to the ferromagnetic chains and low doping concentration make the Co-defective Ca3Co2-xO6 present similar magnetic property with the parent Ca3Co2O6. At the positions of magnetic phase transition and the critical magnetic field of magnetization steps, clear dielectric anomalies can be detected. This result suggests the strong magnetodielectric coupling effect in Ca3Co2-xO6 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) samples.

Photo-induced reversible modification of the Curie–Weiss temperature in paramagnetic gadolinium compounds

Gadolinium oxyhydride GdHO is a photochromic material that darkens under illumination and bleaches back by thermal relaxation. As an inorganic photochromic material that can be easily deposited by magnetron sputtering, GdHO has very interesting potential applications as a functional material, specially for smart glazing applications. However, the underlying reasons behind the photochromic mechanism – which can be instrumental for the correct optimisation of GdHO for different applications – are not completely understood. In this paper, we rely on the well-established magnetic properties of Gd3+ to shed light on this matter. GdHO thin films present paramagnetic behaviour similar to other Gd3+ compounds such as Gd2O3. Illumination of the films result in a reversible increase of the Curie–Weiss temperature pointing to Ruderman–Kittel–Kasuya–Yosida RKKY interactions, which is consistent with the resistivity decrease observed in the photodarkened films.

Magnetism and specific heat of ludwigites Mn1.17Co1.83BO5 and Mn1.39Co1.61BO5

Mn1.17Co1.83BO5 and Mn1.39Co1.61BO5 ludwigites were synthesized by the flux technique and investigated by means of X-ray diffraction, X-ray fluorescence, DC and AC magnetic susceptibility, and specific heat analysis. The crystal structure of both ludwigites belongs to the Pbam space group with a = 9.25 Å, b = 12.41 Å, and c = 3.05 Å for Mn1.17Co1.83BO5 and a = 9.27 Å, b = 12.45 Å, and c = 3.05 Å for Mn1.39Co1.61BO5. The simultaneously observed negative values of the Curie-Weiss temperatures and ferromagnetic-type hysteresis loops allow us to assume that the ferrimagnetic ordering is realized in Mn1.39Co1.61BO5 below TF = 60.8 K, while in Mn1.17Co1.83BO5 in addition to the above mentioned experimental facts the frequency dependencies of the real and imaginary parts of the AC magnetization were observed assuming the presence of the canonical spin-glass state below TSG = 44.5 K. The observed difference in coercive forces of M-H curves at low temperatures can be associated with presence of two spin subsystems for Mn1.17Co1.83BO5.

ESR and magnetization studies of double perovskite Sr[formula omitted]FeNbO6

By pyrolysis of nitrate-organic mixtures, we synthesized double perovskite Sr2Fe0.6NbO5.4. We performed the study of the temperature dependencies of the EPR spectra, DC and AC magnetization, and magnetization isotherms in a wide temperature range of 4–300K. The EPR spectrum is described by the sum of two contributions below 125 K and indicates phase separation of the sample. The paramagnetic part of the inverse magnetic susceptibility is well approximated by the Curie–Weiss law with ΘCW≈−60K. The exchange integrals between iron spins, calculated from the temperature dependence of the ESR integral intensity and the Curie–Weiss temperature, coincide and are equal to J/kB≈10K. The negative sign of the Curie–Weiss temperature and the hysteresis loops indicate the antiferromagnetic canted nature of exchange interactions, which is further confirmed by the presence of a peak in the real part of the AC magnetization and its absence in the imaginary part.

Strongly anisotropic magnetocaloric effect in a dipolar magnet LiGdF4

We report the detailed study of the magnetocaloric effect (MCE) in a dipolar-Heisenberg magnet LiGdF4 using magnetization measurements performed on a single crystal sample. Entropy variation on isothermal demagnetization from the magnetic field up to 3 T is determined in the temperature range 2–10 K for two principal directions of the applied field (parallel and perpendicular to the tetragonal c-axis of the crystal). The MCE is found to be highly anisotropic, with the cooling efficiency being up to twice higher at H∥c. The results are nicely interpreted in the frame of a conventional molecular field approach taking into account considerable anisotropy of the paramagnetic Curie–Weiss temperature. These results are compared to earlier studies of MCE in powder samples of LiGdF4 (Numazawa et al., 2006) as well as with analogous data for other well known magnetocaloric materials. Our findings may open new possibilities to enhance the efficiency of magnetic refrigeration in the liquid helium-4 temperature range.

First-principles study of magnetic interactions and excitations in antiferromagnetic van der Waals material MPX3 (M=Mn, Fe, Co, Ni; X=S, Se)

Transition metal phosphorus trichalcogenides MPX3 (M = Mn, Fe, Co, Ni; X = S, Se), as layered van der Waals antiferromagnetic (AFM) materials, have emerged as a promising platform for exploring two-dimensional (2D) magnetism. Based on density functional theory, we present a comprehensive investigation of the electronic and magnetic properties of MPX3. We calculated the spin exchange interactions as well as magnetocrystalline anisotropy energy. The numerical results reveal that J 3 is AFM in all cases, and J 2 is significantly smaller compared to both J 3 and J 1. This behavior can be understood with regard to exchange paths and electron filling. Compared to other materials within this family, FePS3 and CoPS3 demonstrate significant easy-axis anisotropy. Using the obtained parameters, we estimated the Néel temperature T N and Curie-Weiss temperature , and the results are in good agreement with the experimental observations. We further calculated the magnon spectra and successfully reproduce several typical features observed experimentally. Finally, we give helpful suggestions for the strong constraints about the range of non-negligible magnetic interactions based on the relations between magnon eigenvalues at high-symmetry k points in honeycomb lattices.

Effect of Al3+ substitution on the magnetodielectric properties of the one-dimensional frustrated Ca3Co2O6

Ca3Co2-xAlxO6 (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) were prepared via the conventional sol-gel method. The structure, magnetic, dielectric and magnetodielectric properties were investigated. The Rietveld structural refinement confirms the rhombohedral structure of the samples. The positive Curie-Weiss temperature θ and magnetic coupling exchange constants J indicate the dominant intrachain ferromagnetic interactions in the spin chains. The obvious inhibition effect to equally spaced magnetization steps demonstrates that Al3+ could release the magnetic frustration. With Al3+ substitution, both the magnetization intensity and the critical field of the ferrimagnetism to ferromagnetism transition decrease. The samples present obvious dielectric anomalies around the Curie temperature Tc and the freezing temperature Tf. Meanwhile, the magnetic field dependence of dielectric permittivity decreases suddenly at critical magnetic fields. These results reveal strong magnetodielectric coupling effect in Ca3Co2-xAlxO6. The same sign of Δεr and Δtanδ suggests that the magnetodielectric coupling effect is intrinsic.

A Unique Two-Dimensional Silver(II) Antiferromagnet Cu[Ag(SO4 )2 ] and Perspectives for Its Further Modifications.

Copper(II) silver(II) sulfate crystallizes in a monoclinic CuSO4 -related structure with P21 /n symmetry. This quasi-ternary compound features Ag(SO4 )2 2- layers, while the remaining cationic sites may be occupied either completely or partially by Cu2+ cations, corresponding to the formula of (Cux Ag1-x )[Ag(SO4 )2 ], x=0.6-1.0. CuAg(SO4 )2 is antiferromagnetic with large negative Curie-Weiss temperature of -140 K and shows characteristic ordering phenomenon at 40.4 K. Density functional theory calculations reveal that the strongest superexchange interaction is a two-dimensional antiferromagnetic coupling within Ag(SO4 )2 2- layers, with the superexchange constant J2D of -11.1 meV. This renders CuAg(SO4 )2 the rare representative of layered Ag2+ -based antiferromagnets. Magnetic coupling is facilitated by the strong mixing of Ag d(x2 -y2 ) and O 2p states. Calculations show that M2+ sites in MAg(SO4 )2 can be occupied with other similar cations such as Zn2+ , Cd2+ , Ni2+ , Co2+ , and Mg2+ .

Magnetic ordering in Ce substituted zirconite-YCrO4 nanostructures: focus on tunable energy bandgap and local-atomic environment

This study presents a comprehensive investigation of the structural, magnetic, electronic, and optical spectroscopic properties of tetragonal Zirconite Y1−x Ce x CrO4 polycrystals that were synthesized at various temperature ranges. The YCrO4 phase in its pristine state demonstrates ferromagnetic (FM) ordering, characterized by a Curie temperature, T C ∼ 9.3 K. Nevertheless, the introduction of magnetic Ce3+ in place of Y3+ ions results in a reduction of the T C and the appearance of a weak antiferromagnetic (AFM) behaviour, as indicated by the presence of a negative Curie–Weiss temperature (−10 K ≲ θ CW ≲ −30 K). It is observed that the introduction of moderate levels of Ce substitution leads to a significant increase in thermal irreversibility in the magnetization difference between field-cooled and zero-field-cooled states ΔM (M FC − M ZFC). This phenomenon indicates the substantial influence of magneto-crystalline anisotropy that exists within the system. Field-dependent magnetization data exhibits higher saturation magnetization values (M S ≳ (2.7 to 4.4) × 103 emu mole−1) and higher magneto-crystalline anisotropy (K 1 ∼ 2.18 to 3.41 J m−3) for the dilute dispersion of Ce (x ≤ 0.05). Local atomic environment probed by the electron spin resonance clearly indicates the presence of hyperfine splitting of Cr5+ spectra having a single d-electron () with orbital configuration bearing the possible doublet: On the other hand, the rare-earth Ce3+ spectra show hyperfine-doublets as and Finally, the energy band-gap (E g = 2.14 to 2.38 eV, for x ∼ 0 to 0.1) determined from the diffuse reflectance spectroscopy reveals the emergence of intermediate localized states upon substitution of Ce3+.

Sol-gel synthesis of LiSICON compound and their studies by X-ray powder diffraction, infrared, magnetic and impedance spectroscopy

Compounds with the formula LiNi0.9Mn0.1PO4 (LNMP) are prepared using a sol-gel synthesis method. The compound has been structurally characterized by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, magnetic measurements, and electrical impedance spectroscopy. The structure of the sample was orthorhombic with the Pnma space group. The study by infrared spectroscopy reveals the existence of P-O band vibrations, is attributed to the phosphate ion PO4. The morphological characterization shows that the size of the particles is of the order of 0.29 μm. The negative Curie-Weiss temperature θCW= -49.67 K suggests an antiferromagnetic interaction between the cationic MII (M = Ni/Mn) mediated through the oxygen of the PO4 bridged ion. We performed the conductivity analysis of the sample at different temperatures and frequencies, which proves that the general conduction is predominantly by the correlated barrier hopping mechanism (CBH) model with the diffusion possibility of Li+ in tunnels along the b-direction. This 2D model of conduction agrees with the computed calculation of minimum pathway energy migration.

Incommensurate Antiferromagnetic Order in Weakly Frustrated Two-Dimensional van der Waals Insulator CrPSe3.

Although magnetic order is suppressed by a strong frustration, it appears in complex forms such as a cycloid or spin density wave in weakly frustrated systems. Herein, we report a weakly magnetically frustrated two-dimensional (2D) van der Waals material CrPSe3. Polycrystalline CrPSe3 was synthesized at an optimized temperature of 700 °C to avoid the formation of any secondary phases (e.g., Cr2Se3). The antiferromagnetic transition appeared at TN ≈ 127 K with a large Curie-Weiss temperature θCW ≈ -301 K via magnetic susceptibility measurements, indicating weak frustration in CrPSe3 with a frustration factor of f (|θCW|/TN) ≈ 2.4. Evidently, the formation of a long-range incommensurate antiferromagnetic order was revealed by neutron diffraction measurements at low temperatures (below 120 K). The monoclinic crystal structure of the C2/m symmetry is preserved over the studied temperature range down to 20 K, as confirmed by Raman spectroscopy measurements. Our findings on the incommensurate antiferromagnetic order in 2D magnetic materials, not previously observed in the MPX3 family, are expected to enrich the physics of magnetism at the 2D limit, thereby opening opportunities for their practical applications in spintronics and quantum devices.

Influence of Ni substitution on the magnetic properties of PrCoO3: A comprehensive study

The influence of nickel (Ni) ions on the structural and magnetic properties of PrCo1-xNixO3 perovskites was investigated. The samples were prepared using a sol-gel chemical auto-combustion route. The Rietveld refined X-ray diffraction patterns show that all samples were single-phase polycrystalline with orthorhombic (Pbnm) perovskite symmetry. Fourier transform infrared spectroscopy (FTIR) showed that with increasing Ni dopant content, the spin state changed from a low to an intermediate spin state (LS→IS), leading to an increase in the Co3+ population in the IS state, which improved the stability of the IS state. X-ray photoelectron spectroscopy confirmed the presence of mixed valence states (Co3+/Co4+) and oxygen vacancies. Ni-substituted PrCoO3 compounds exhibited mixed magnetic phases, which were separated by a theoretical model. The susceptibility curves were fitted with the Curie–Weiss law, and the negative value of the Curie–Weiss temperature indicated a strong predominance of antiferromagnetic (AFM) interactions over ferromagnetic (FM) ordering. However, when the Ni content in the host lattice increased, the FM coupling via double exchange became stronger. Thus, saturated FM ordering was achieved with an optimum doping level of Ni ions.

Structural and spin-glass properties of single crystal J eff = ½ pyrochlore antiferromagnet NaCdCo2F7: correlating T f with magnetic-bond-disorder

Weak bond disorder disrupts the expected spin-liquid ground-state of the ideal S = 1/2 Heisenberg pyrochlore antiferromagnet. Here we introduce a single crystal study of the structural and magnetic properties of the bond-disordered pyrochlore NaCdCo2F7. The magnetic susceptibility appears isotropic, with a large negative Curie-Weiss temperature (θCW = −108(1) K), however no magnetic order is observed on cooling until a spin-glass transition at T f = 4.0 K. AC-susceptibility measurements show a frequency-dependent shift of the associated cusp in χ’ at T f, that can be fitted well by the empirical Vogel-Fulcher law. The magnetic moment of μ eff = 5.4(1) μ B/Co2+ indicates a significant orbital contribution and heat capacity measurements show that down to 1.8 K, well below T f, only S mag ∼ Rln(2) of the magnetic entropy is recovered, suggestive of residual continued dynamics. Structural and magnetism comparisons are made with the other known members of the NaA’’Co2F7 family (A″ = Ca2+, Sr2+), confirming the expected relationship between spin-glass freezing temperature, and extent of magnetic bond disorder brought about by the size mismatch between A-site ions.

K2Ni(SeO3)2: A Perfect S = 1 Triangular-Lattice Antiferromagnet with Strong Geometric Frustration and Easy-Plane Anisotropy

We synthesized a single crystal of K2Ni(SeO3)2 (S = 1) with an equilateral triangular lattice (space group R-3m). The magnetic susceptibility χ(T) and heat capacity Cp(T) show that the compound is antiferromagnetically ordered at TN ≈ 7 K. The Curie–Weiss temperature is about θCW = −72.41 and −71.83 K when the field is applied along the ab plane (H//ab) and parallel to the c axis (H//c), respectively, indicating a strong geometric frustration (f ≈ 10). Both the χ(T) and M(H) point to the presence of easy-plane anisotropy. Density functional theory (DFT) calculations estimate the intraplane exchange (J/kB = −19.04 K) and the interplane exchange (J′/kB = −0.01 K), proving the excellent two-dimensionality. The 50 T high-field magnetization M(H) at 2 K indicates a sign of 1/3 magnetization plateau. The high-field electron spin resonance demonstrates the antiferromagnetic resonance modes with easy-plane anisotropy, yielding J highly consistent with the DFT result. Thus, K2Ni(SeO3)2 is a perfect triangular-lattice antiferromagnet with strong frustration and easy-plane anisotropy.

Magnetic properties of S=12 distorted J1−J2 honeycomb lattice compound NaCuIn(PO4)2

The subtle interplay between low-dimensionality and spin correlations can lead to exotic ground states with unconventional excitations in two-dimensional honeycomb-lattice-based quantum magnets. Herein, we present the structural, magnetic, and heat capacity measurements; density functional theory $+$ Hubbard $U$ ($\mathrm{DFT}+U$) based electronic structure calculations; and quantum Monte Carlo simulations for $\mathrm{NaCuIn}{({\mathrm{PO}}_{4})}_{2}$. The structure of $\mathrm{NaCuIn}{({\mathrm{PO}}_{4})}_{2}$ consists of a well-separated, $\mathit{S}=\frac{1}{2}$ distorted ${\mathit{J}}_{1}\text{\ensuremath{-}}{\mathit{J}}_{2}$ honeycomb layer which is a combination of the magnetic couplings ${\mathit{J}}_{1}$ (forming spin dimers) and ${\mathit{J}}_{2}$ (constituting spin chains). At high temperatures, the magnetic susceptibility $\ensuremath{\chi}(T)$ follows paramagnetic behavior with a Curie-Weiss temperature ${\ensuremath{\theta}}_{\mathrm{CW}}\ensuremath{\approx}\ensuremath{-}16$ K, implying the presence of antiferromagnetic interactions. A broad maximum is observed at about $13\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in $\ensuremath{\chi}(T)$, indicating the presence of short-range spin correlations. The quantum Monte Carlo simulations using the $\mathit{S}=\frac{1}{2}\phantom{\rule{4pt}{0ex}}{\mathit{J}}_{1}\text{\ensuremath{-}}{\mathit{J}}_{2}$ Heisenberg model on a distorted honeycomb lattice are in good agreement with the measured magnetic susceptibility data. The obtained ratio of the exchange couplings ($\frac{{\mathit{J}}_{2}}{{\mathit{J}}_{1}}$) is 2.63, which is consistent with the value obtained from our $\mathrm{DFT}+U$ calculations. The title material undergoes a magnetic long-range order at 0.4 K in the heat capacity, which is suppressed with an applied magnetic field of 10 kOe. The magnetic heat capacity data follow a linear temperature-dependent behavior well above the transition temperature, suggesting the presence of gapless excitations. The observed behavior can be attributed to the presence of low connectivity and weak magnetic frustration in this two-dimensional distorted honeycomb lattice.

Cationic nonstoichiometry, structural and magnetic properties of hexagonal Tm2-xMnxO3 manganites

We studied the mechanism of formation of cation-nonstoichiometric compositions of the Tm2-xMnxO3 (x = 0.96, 0.98, 1, 1.02, 1.04, 1.06) solid solution with a hexagonal crystal structure. The entire region of homogeneity of compositions with an excess/deficiency of Mn and Tm was covered. Their structural and magnetic properties were studied by X-ray diffraction and magnetometry. The analysis of the concentration dependence of the structural parameters allows us to conclude that the formation of compositions with an excess of Tm occurs through the formation of vacancies in the Mn sublattice. The mechanism of formation of solid solutions with an excess of Mn includes the reaction of manganese disproportionation: 2Mn3+=Mn4++Mn2+. The Mn2+ ions formed as a result of this reaction occupy thulium sites, while manganese sites are occupied by Mn3+ and Mn4+ ions. Magnetic properties have been studied as functions of temperature in the temperature range 5 – 300 K. It was established that all the samples undergo a transition from the high-temperature PM state to AF one at T = TN1. The temperature TN1 both at x < 1 and x > 1 is reduced and takes a value in the range of 81–84 K. With decreasing temperature (T < TN1) in samples with x = 0.96, 1.04, 1.06 an additional first-order transition to a new AF state is observed in the vicinity of T∼45 K. The Curie-Weiss temperature ΘCW monotonically decreases for compositions with x < 1. At the same time with x > 1 a nonlinear dependence of ΘCW (x) is observed.

Evaluation of the critical behavior near ferromagnetic to paramagnetic phase transition in CrTe1-xSex alloys: An experimental study

We used the conventional solid-state reaction method to prepare stoichiometric samples of CrTe1-xSex, where 0 ≤ x ≤ 0.10, and investigated the structural and critical behavior of the prepared samples. Room temperature powder X-ray diffraction, along with Rietveld refinement, revealed the emergence of the NiAs structure with P63/mmc (194) space group with increasing Se substitution. The high-temperature linear fit to inverse of the dc-susceptibility versus temperature for the mother sample resulted in an effective moment of 3.65μB Cr with Curie-Weiss temperature near 335K, which is slightly higher than the Tc of ∼332K obtained from the inflection point of magnetization versus temperature. Magnetization isotherms were employed to investigate the critical behavior of ferromagnetic CrTe1-xSex with 0.0 ≤ x ≤ 0.10 near their Curie temperatures (Tc). The magnetic behavior near Tc was found to follow 3D mean-field critical exponents with a second-order phase transition in all samples investigated. We fine-tuned the critical exponents (β, γ, and δ) using a combination of an iteration technique, the Kouvel-Fisher method, and modified Arrott plots. All samples follow a mean field behavior, with Tc ranging from 298 to 340K. The acquired values exhibit self-consistency, as indicated by the results from the Widom scaling relation. Furthermore, the magnetization isotherms exhibit a universal scaling behavior, providing additional credence to the calculated critical exponents.

High-pressure synthesis and magnetic properties of tetragonal R2BaCuO5 (R = Sm and Eu).

We report the experimental discovery of a new structural phase of well-known orthorhombic R 2BaCuO5 (R = Sm and Eu), exhibiting a tetragonal crystal structure with space group . The high-pressure tetragonal phase is isostructural with the brown phase R 2BaCuO5 (R = La, Pr, and Nd). In this structure, the Cu ions form an isolated square planar environment, contrary to the orthorhombic phase, where the Cu ions are located in a distorted square pyramid. Magnetization and specific heat measurements reveal the long-range antiferromagnetic order of the Cu2+ and/or Sm3+ moments for the Sm-sample, with the magnetic specific heat accounting for only 35% of the magnetic entropy. Interestingly, the Eu-sample remains paramagnetic down to the lowest temperature. The high Curie-Weiss temperature of -140K and magnetic entropy of 3% of the expected value indicates that the system is highly frustrated. We estimated the isothermal entropy change and investigated the magnetocaloric effect for Eu2BaCuO5, and the maximum entropy change detected at a field of 70kOe at 3K reaches 5.6Jkg-1K-1.

Triangular lattice Hubbard model physics at intermediate temperatures

Moire systems offer an exciting playground to study many-body effects of strongly correlated electrons in regimes that are not easily accessible in conventional material settings. Motivated by a recent experiment on $\text{WSe}_2/\text{WS}_2$ moire bilayers [Y. Tang et al., Nature 579, 353-358 (2020)], which realizes a triangular superlattice with a small hopping (of approximately 10 Kelvin), with tunable density of holes, we explore the Hubbard model on the triangular lattice for intermediate temperatures $t \lesssim T < U$. Employing finite temperature Lanczos calculations, and closely following the fitting protocols used in the experiment, we recover the observed trends in the reported Curie-Weiss temperature $\Theta$ with filling, using the reported interaction strength $U/t=20$. We focus on the large increase of $|\Theta|$ on decreasing the density below half filling and the sign change of $\Theta$ at higher fillings, which signals the onset of ferromagnetism. The increase in $|\Theta|$ is also seen in the $t$-$J$ model (the low energy limit of the Hubbard model) in the intermediate temperature range, which we clarify is opposite to the trend in its high temperature limit. Differences between the low, intermediate and high temperature regimes are discussed. Our numerical calculations also capture the crossover between short-range antiferromagnetic to ferromagnetic order in the intermediate temperature regime, a result broadly consistent with the experimental findings. We find that this behavior is a finite-temperature remnant of the underlying zero temperature phase transition, which we explore with ground state density matrix renormalization group calculations. We provide evidence of ferromagnetism characterized by weak (but robust) correlations that explain the small $\Theta$ seen in the experiment.

Magnetism in frustrated Kondo and non-Kondo intermetallics: CeInCu2 versus NdInCu2

Single crystalline intermetallics ${\mathrm{CeInCu}}_{2}$ and ${\mathrm{NdInCu}}_{2}$, where the rare earth ions occupy geometrically frustrated fcc lattice of Heusler-type structure, have been studied comparatively to shed light on the ground-state magnetism derived from Kondo physics and/or spin frustration competing with the Ruderman-Kittel-Kasuya-Yosida interaction. ${\mathrm{CeInCu}}_{2}$ is distinct from ${\mathrm{NdInCu}}_{2}$ due to the significant Kondo effect that is absent in the latter. They order antiferromagnetically at ${T}_{N}\phantom{\rule{0.16em}{0ex}}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}1.4$ and 2.0 K with large paramagnetic Curie-Weiss temperature of $\ensuremath{-}35.4$ K and $\ensuremath{-}41.1$ K, respectively. The electronic specific-heat coefficient $\ensuremath{\gamma}$ = $C/T$ ($T\phantom{\rule{0.16em}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{0.16em}{0ex}}0$) = 870 mJ ${\mathrm{mol}}^{\ensuremath{-}1}\phantom{\rule{4pt}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}$ in ${\mathrm{CeInCu}}_{2}$ is significantly enhanced, much larger than 180 mJ ${\mathrm{mol}}^{\ensuremath{-}1}\phantom{\rule{4pt}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}$ of the latter that is also enhanced albeit its non-Kondo nature. For both compounds, the Kadowaki-Woods ratio deviates greatly from the standard value expected from a Kramers doublet ground state, which, however, can be restored if one considers a smaller but still sizable $\ensuremath{\gamma}$ estimated from the paramagnetic state. Likewise, the Kondo temperature of ${\mathrm{CeInCu}}_{2}$ is revised to be ${T}_{K}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}$ 13 K that is double the literature values, manifesting a major effect of spin frustration to low-temperature thermodynamics beyond the Kondo physics. Similarities between the two compounds is also noticed in their temperature-field phase diagrams in spite of their thermodynamic distinctions in the thermal expansion and the Gr\"uneisen ratio, which are much more sensitive to Kondo hybridization than to geometrical frustration.