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Origin of the non-Fermi-liquid behavior in CeRh2As2
Authors:
P. Khanenko,
D. Hafner,
K. Semeniuk,
J. Banda,
T. Luehmann,
F. Baertl,
T. Kotte,
J. Wosnitza,
G. Zwicknagl,
C. Geibel,
J. F. Landaeta,
S. Khim,
E. Hassinger,
M. Brando
Abstract:
Unconventional superconductivity in heavy-fermion systems appears often near magnetic quantum critical points (QCPs). This seems to be the case also for CeRh2As2 (Tc $\approx$ 0.31 K). CeRh2As2 shows two superconducting (SC) phases, SC1 and SC2, for a magnetic field along the c axis of the tetragonal unit cell, but only the SC1 phase is observed for a field along the basal plane. Furthermore, anot…
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Unconventional superconductivity in heavy-fermion systems appears often near magnetic quantum critical points (QCPs). This seems to be the case also for CeRh2As2 (Tc $\approx$ 0.31 K). CeRh2As2 shows two superconducting (SC) phases, SC1 and SC2, for a magnetic field along the c axis of the tetragonal unit cell, but only the SC1 phase is observed for a field along the basal plane. Furthermore, another ordered state (phase-I) is observed below T0 $\approx$ 0.48 K whose nature is still unclear: Thermodynamic and magnetic measurements pointed to a non magnetic multipolar state, but recent $μ$SR and NQR/NMR experiments have clearly detected antiferromagnetic (AFM) order below T0 . Also, quasi-two-dimensional AFM fluctuations were observed in NMR and neutron-scattering experiments above T0. The proximity of a QCP is indicated by non-Fermi-liquid (NFL) behavior observed above the ordered states in both specific heat $C(T)/T \propto T^{-0.6}$ and resistivity $ρ(T) \propto T^{0.5}$. These T-dependencies are not compatible with any generic AFM QCP. Because of the strong magnetic-field anisotropy of both the SC phase and phase I, it is possible to study a field-induced SC QCP as well a phase-I QCP by varying the angle $α$ between the field and the c axis. Thus, by examining the behavior of the electronic specific-heat coefficient C(T)/T across these QCPs, we can determine which phase is associated with the NFL behavior. Here, we present low-temperature specific-heat measurements taken in a magnetic field as high as 21 T applied at several angles $α$. We observe that the NFL behavior does very weakly depend on the field and on the angle $α$, a result that is at odd with that observations in standard magnetic QCPs. This suggests a nonmagnetic origin of the quantum critical fluctuations.
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Submitted 18 September, 2024;
originally announced September 2024.
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Physical properties of the ferromagnetic quantum critical system YbNi$_4$(P$_{1-x}$As$_{x}$)$_2$
Authors:
Kristin Kliemt,
Jacintha Banda,
Pavlo Khanenko,
Ali Scherzad,
Ulrike Stockert,
Anna Efimenko,
Kurt Kummer,
Cornelius Krellner,
Manuel Brando
Abstract:
We report on single crystal growth and physical properties of the quantum critical Kondo-lattice system YbNi$_4$(P$_{1-x}$As$_{x}$)$_2$ with $0\leq x\leq 1$ which hosts a ferromagnetic quantum critical point at $x \approx 0.1$. We performed measurements of the magnetization, electrical resistivity, thermopower, heat capacity, and resonant X-ray emission spectroscopy. Arsenic substitution leads to…
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We report on single crystal growth and physical properties of the quantum critical Kondo-lattice system YbNi$_4$(P$_{1-x}$As$_{x}$)$_2$ with $0\leq x\leq 1$ which hosts a ferromagnetic quantum critical point at $x \approx 0.1$. We performed measurements of the magnetization, electrical resistivity, thermopower, heat capacity, and resonant X-ray emission spectroscopy. Arsenic substitution leads to a homogeneous increase of the unit-cell volume, with well-defined As-concentrations in large parts of the single crystals. All data consistently show that with increasing $x$ the Kondo temperature increases, while the magnetic anisotropy observed at low $x$ fully vanishes towards $x=1$. Consequently, at low temperatures, the system shows a crossover from pronounced non-Fermi liquid behaviour for $x \leq 0.2$ to a Fermi liquid behavior for $x > 0.2$ with weak correlations. There is a continuous change in Yb valence from nearly trivalent at low $x$ to a slightly lower value for $x = 0.6$, which correlates with the Kondo temperature. Interestingly, specific heat measurements at very low temperatures show that $C/T$ strongly increases towards lower $T$ for $x = 0.13$ and $x = 0.2$ with a very similar power law. This suggests that in YbNi$_4$(P$_{1-x}$As$_{x}$)$_2$ a quantum critical region rather than a quantum critical point might exist.
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Submitted 8 September, 2024;
originally announced September 2024.
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Metallic local-moment magnetocalorics as a route to cryogenic refrigeration
Authors:
Thomas Gruner,
Jiasheng Chen,
Dongjin Jang,
Jacintha Banda,
Christoph Geibel,
Manuel Brando,
F. Malte Grosche
Abstract:
Commercial adiabatic demagnetisation refrigerators still employ the same hydrated salts that were first introduced over 85 years ago. The inherent limitations of these insulating magnetocalorics - poor thermal conductivity at sub-Kelvin temperatures, low entropy density, corrosiveness - can be overcome by a new generation of rare-earth based metallic magnetocalorics. Here, we present the metallic…
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Commercial adiabatic demagnetisation refrigerators still employ the same hydrated salts that were first introduced over 85 years ago. The inherent limitations of these insulating magnetocalorics - poor thermal conductivity at sub-Kelvin temperatures, low entropy density, corrosiveness - can be overcome by a new generation of rare-earth based metallic magnetocalorics. Here, we present the metallic magnetocaloric YbNi1.6 Sn as an attractive alternative to conventional refrigerants. YbNi1.6Sn retains high entropy into the 100 mK regime and avoids the noble metal constituents of alternative refrigerants. Demagnetisation tests demonstrate that YbNi1.6Sn enables economical and durable alternatives to traditional cooling devices for temperatures reaching below 120 mK. We find that the magnetocaloric properties of this material are facilitated by unusually small Kondo and RKKY interactions, which position YbNi1.6Sn in the extreme local moment limit on the generalised Kondo lattice phase diagram.
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Submitted 1 May, 2024;
originally announced May 2024.
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Electronuclear Quantum Criticality
Authors:
J. Banda,
D. Hafner,
J. F. Landaeta,
E. Hassinger,
K. Mitsumoto,
M. Giovannini,
J. G. Sereni,
C. Geibel,
M. Brando
Abstract:
We present here a rare example of electronuclear quantum criticality in a metal. The compound YbCu4.6Au0.4 is located at an unconventional quantum critical point (QCP). In this material the relevant Kondo and RKKY exchange interactions are very weak, of the order of 1 K. Furthermore, there is strong competition between antiferromagnetic and ferromagnetic correlations, possibly due to geometrical f…
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We present here a rare example of electronuclear quantum criticality in a metal. The compound YbCu4.6Au0.4 is located at an unconventional quantum critical point (QCP). In this material the relevant Kondo and RKKY exchange interactions are very weak, of the order of 1 K. Furthermore, there is strong competition between antiferromagnetic and ferromagnetic correlations, possibly due to geometrical frustration within the fcc Yb sublattice. This causes strong spin fluctuations which prevent the system to order magnetically. Because of the very low Kondo temperature the Yb3+ 4f-electrons couple weakly with the conduction electrons allowing the coupling to the nuclear moments of the 171Yb and 173Yb isotopes to become important. Thus, the quantum critical fluctuations observed at the QCP do not originate from purely electronic states but from entangled electronuclear states. This is evidenced by the anomalous temperature and field dependence of the specific heat at low temperatures.
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Submitted 29 August, 2023;
originally announced August 2023.
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Decoupling multi-phase superconductivity from normal state ordering in CeRh$_2$As$_2$
Authors:
Konstantin Semeniuk,
Daniel Hafner,
Pavlo Khanenko,
Thomas Lühmann,
Jacintha Banda,
Javier F. Landaeta,
Christoph Geibel,
Seunghyun Khim,
Elena Hassinger,
Manuel Brando
Abstract:
CeRh$_2$As$_2$ is a multi-phase superconductor with $T_{\textrm{c}}=0.26\,\textrm{K}$. The two superconducting (SC) phases, SC1 and SC2, observed for a magnetic field $H$ parallel to the $c$ axis of the tetragonal unit cell, have been interpreted as even- and odd-parity SC states, separated by a phase boundary at $μ_{\textrm{0}}H^{*}=4\,\textrm{T}$. Such parity switching is possible due to a stron…
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CeRh$_2$As$_2$ is a multi-phase superconductor with $T_{\textrm{c}}=0.26\,\textrm{K}$. The two superconducting (SC) phases, SC1 and SC2, observed for a magnetic field $H$ parallel to the $c$ axis of the tetragonal unit cell, have been interpreted as even- and odd-parity SC states, separated by a phase boundary at $μ_{\textrm{0}}H^{*}=4\,\textrm{T}$. Such parity switching is possible due to a strong Rashba spin-orbit coupling at the Ce sites located in locally non-centrosymmetric environments of the globally centrosymmetric lattice. Existence of another ordered state (Phase I) below a temperature $T_{\textrm{0}}\approx0.4\,\textrm{K}$ suggests an alternative interpretation of the $H^{*}$ transition: It separates a mixed SC+I (SC1) and a pure SC (SC2) state. Here, we present a detailed study of higher quality single crystals of CeRh$_2$As$_2$, showing much sharper signatures at $T_{\textrm{c}}=0.31\,\textrm{K}$ and $T_{\textrm{0}}=0.48\,\textrm{K}$. We refine the $T$-$H$ phase diagram of CeRh$_2$As$_2$ and demonstrate that $T_{0}(H)$ and $T_{\textrm{c}}(H)$ lines meet at $μ_{\textrm{0}}H\approx6\,\textrm{T}$, well above $H^{*}$, implying no influence of Phase I on the SC phase switching. A basic analysis with the Ginzburg-Landau theory indicates a weak competition between the two orders.
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Submitted 10 January, 2024; v1 submitted 22 January, 2023;
originally announced January 2023.
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Low-Temperature Thermal Conductivity of CeRh$_{2}$As$_{2}$
Authors:
Seita Onishi,
Ulrike Stockert,
Seunghyun Khim,
Jacintha Banda,
Manuel Brando,
Elena Hassinger
Abstract:
CeRh$_2$As$_2$ is a rare unconventional superconductor ($T_c=0.26$ K) characterized by two adjacent superconducting phases for a magnetic field $H \parallel c$-axis of the tetragonal crystal structure. Antiferromagnetic order, quadrupole-density-wave order ($T_0 = 0.4$ K) and the proximity of this material to a quantum-critical point have also been reported: The coexistence of these phenomena with…
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CeRh$_2$As$_2$ is a rare unconventional superconductor ($T_c=0.26$ K) characterized by two adjacent superconducting phases for a magnetic field $H \parallel c$-axis of the tetragonal crystal structure. Antiferromagnetic order, quadrupole-density-wave order ($T_0 = 0.4$ K) and the proximity of this material to a quantum-critical point have also been reported: The coexistence of these phenomena with superconductivity is currently under discussion. Here, we present thermal conductivity and electrical resistivity measurements on a single crystal of CeRh$_2$As$_2$ between 60 mK and 200 K and in magnetic fields ($H \parallel c$) up to 8 T. Our measurements at low $T$ verify the Wiedemann-Franz law within the error bars. The $T$ dependence of the thermal conductivity $κ(T)$ shows a pronounced drop below $T_c$ which is also field dependent and thus interpreted as the signature of superconductivity. However, the large residual resistivity and the lack of sharp anomalies in $κ(T)$ at the expected transition temperatures clearly indicate that samples of much higher purity are required to gain more information about the superconducting gap structure.
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Submitted 25 February, 2022;
originally announced February 2022.
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Possible quadrupole density wave in the superconducting Kondo lattice CeRh2As2
Authors:
D. Hafner,
P. Khanenko,
E. -O. Eljaouhari,
R. Küchler,
J. Banda,
N. Bannor,
T. Lühmann,
J. F. Landaeta,
S. Mishra,
I. Sheikin,
E. Hassinger,
S. Khim,
C. Geibel,
G. Zwicknagl,
M. Brando
Abstract:
CeRh2As2 has recently been reported to be a rare case of multi-phase unconventional superconductor [S. Khim et al., arXiv:2101.09522] close to a quantum critical point (QCP). Here, we present a comprehensive study of its normal state properties and of the phase (I) below To ~ 0.4 K which preempts superconductivity at Tc = 0.26 K. The 2nd-order phase transition at To presents signatures in specific…
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CeRh2As2 has recently been reported to be a rare case of multi-phase unconventional superconductor [S. Khim et al., arXiv:2101.09522] close to a quantum critical point (QCP). Here, we present a comprehensive study of its normal state properties and of the phase (I) below To ~ 0.4 K which preempts superconductivity at Tc = 0.26 K. The 2nd-order phase transition at To presents signatures in specific heat and thermal expansion, but none in magnetization and ac-susceptibility, indicating a non-magnetic origin of phase I. In addition, an upturn of the in-plane resistivity at To points to a gap opening at the Fermi level in the basal plane. Thermal expansion indicates a strong positive pressure dependence of To , dTo/dp = 1.5 K/GPa, in contrast to the strong negative pressure coefficient observed for magnetic order in Ce-based Kondo lattices close to a QCP. Similarly, an in-plane magnetic field shifts To to higher temperatures and transforms phase I into another non-magnetic phase (II) through a 1st-order phase transition at about 9 T. Using renormalized band structure calculations, we found that the Kondo effect (TK ~ 30 K) leads to substantial mixing of the excited crystalline-electric-field (CEF) states into the ground state. This allows quadrupolar degrees of freedom in the resulting heavy bands at the Fermi level which are prone to nesting. The huge sensitivity of the quadrupole moment on hybridization together with nesting would cause an unprecedented case of phase transition into a quadrupole-density-wave (QDW) state at a temperature To << TK , which would explain the nature of phase I and II.
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Submitted 13 August, 2021;
originally announced August 2021.
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Field-induced transition from even to odd parity superconductivity in CeRh$_2$As$_2$
Authors:
S. Khim,
J. F. Landaeta,
J. Banda,
N. Bannor,
M. Brando,
P. M. R. Brydon,
D. Hafner,
R. Küchler,
R. Cardoso-Gil,
U. Stockert,
A. P. Mackenzie,
D. F. Agterberg,
C. Geibel,
E. Hassinger
Abstract:
We report the discovery of two-phase unconventional superconductivity in CeRh$_2$As$_2$. Using thermodynamic probes, we establish that the superconducting critical field of its high-field phase is as high as 14 T, remarkable in a material whose transition temperature is 0.26 K. Furthermore, a $c$-axis field drives a transition between two different superconducting phases. In spite of the fact that…
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We report the discovery of two-phase unconventional superconductivity in CeRh$_2$As$_2$. Using thermodynamic probes, we establish that the superconducting critical field of its high-field phase is as high as 14 T, remarkable in a material whose transition temperature is 0.26 K. Furthermore, a $c$-axis field drives a transition between two different superconducting phases. In spite of the fact that CeRh$_2$As$_2$ is globally centrosymmetric, we show that local inversion-symmetry breaking at the Ce sites enables Rashba spin-orbit coupling to play a key role in the underlying physics. More detailed analysis identifies the transition from the low- to high-field states to be associated with one between states of even and odd parity.
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Submitted 23 January, 2021;
originally announced January 2021.
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Unconventional bulk superconductivity in YFe$_2$Ge$_2$ single crystals
Authors:
Jiasheng Chen,
Monika B. Gamża,
Jacintha Banda,
Keiron Murphy,
James Tarrant,
Manuel Brando,
F. Malte Grosche
Abstract:
Using a new horizontal flux growth technique to produce high quality crystals of the unconventional superconductor YFe$_2$Ge$_2$ has led to a seven-fold reduction in disorder scattering, resulting in mm-sized crystals with residual resistivities $\simeq \SI{0.45}{\micro\ohm\centi\meter}$, resistivity ratios $\simeq 430$ and sharp superconducting heat capacity anomalies. This enables searching mult…
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Using a new horizontal flux growth technique to produce high quality crystals of the unconventional superconductor YFe$_2$Ge$_2$ has led to a seven-fold reduction in disorder scattering, resulting in mm-sized crystals with residual resistivities $\simeq \SI{0.45}{\micro\ohm\centi\meter}$, resistivity ratios $\simeq 430$ and sharp superconducting heat capacity anomalies. This enables searching multi-probe experiments investigating the normal and superconducting states of YFe$_2$Ge$_2$. Low temperature heat capacity measurements suggest a significant residual Sommerfeld coefficient, consistent with in-gap states induced by residual disorder as predicted for a sign-changing order parameter.
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Submitted 27 July, 2020;
originally announced July 2020.
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Bulk properties of single crystals of the valence-unstable compound SmRh$_2$Si$_2$
Authors:
Kristin Kliemt,
Jacintha Banda,
Christoph Geibel,
Manuel Brando,
Cornelius Krellner
Abstract:
We present the crystal growth as well as the structural, chemical and physical chracterization of SmRh$_2$Si$_2$ single crystals. Their ground state is antiferromagnetic, as indicated by the behaviour of the magnetic susceptibility and the specific heat at the second order phase transition observed at T$_{\rm N}$ = 64 K. The Sommerfeld coefficient is small and similar to that of LuRh$_2$Si$_2$ wit…
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We present the crystal growth as well as the structural, chemical and physical chracterization of SmRh$_2$Si$_2$ single crystals. Their ground state is antiferromagnetic, as indicated by the behaviour of the magnetic susceptibility and the specific heat at the second order phase transition observed at T$_{\rm N}$ = 64 K. The Sommerfeld coefficient is small and similar to that of LuRh$_2$Si$_2$ with $γ_0\approx$ J/(molK$^2$). Susceptibility measurements show no Curie-Weiss behaviour at high temperatures which is a consequence of the large Van-Vleck contribution of the excited multiplets of Sm$^{3+}$. Previous angle-resolved photoemission studies showed that at 10 K, the valence of the Sm ions is smaller than three at the surface as well as in the bulk, suggesting a possible Kondo screening of the Sm$^{3+}$ ions. This could not be observed in our thermodynamic and transport measurements.
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Submitted 2 May, 2019;
originally announced May 2019.
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Kondo-lattice ferromagnets and their peculiar order along the magnetically hard axis
Authors:
Daniel Hafner,
Binod K. Rai,
Jacintha Banda,
Kristin Kliemt,
Cornelius Krellner,
Jörg Sichelschmidt,
Emilia Morosan,
Christoph Geibel,
Manuel Brando
Abstract:
We show that Ce- and Yb-based Kondo-lattice ferromagnets order mainly along the magnetically hard direction of the ground state Kramers doublet determined by crystalline electric field (CEF). Here we argue that this peculiar phenomenon, that was believed to be rare, is instead the standard case. Moreover, it seems to be independent on the Curie temperature $T_\mathrm{C}$, crystalline structure, si…
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We show that Ce- and Yb-based Kondo-lattice ferromagnets order mainly along the magnetically hard direction of the ground state Kramers doublet determined by crystalline electric field (CEF). Here we argue that this peculiar phenomenon, that was believed to be rare, is instead the standard case. Moreover, it seems to be independent on the Curie temperature $T_\mathrm{C}$, crystalline structure, size of the ordered moment and type of ground state wave function. On the other hand, all these systems show the Kondo coherence maximum in the temperature dependence of the resistivity just above $T_\mathrm{C}$ which indicates a Kondo temperature of a few Kelvin. An important role of fluctuations is indicated by the non-mean-field like transition in specific heat measurements as well as by the suppression of this effect by a strong Ising-like anisotropy. We discuss possible theoretical scenarios.
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Submitted 18 March, 2019; v1 submitted 14 January, 2019;
originally announced January 2019.
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Ferromagnetic ordering along the hard axis in the Kondo lattice YbIr3Ge7
Authors:
Binod K. Rai,
Macy Stavinoha,
J. Banda,
D. Hafner,
Katherine A. Benavides,
D. A. Sokolov,
Julia Chan,
M. Brando,
C. -L. Huang,
E. Morosan
Abstract:
Ferromagnetic Kondo lattice compounds are far less common than their antiferromagnetic analogs. In this work, we report the discovery of a new ferromagnetic Kondo lattice compound, YbIr3Ge7. Like almost all ferromagnetic Kondo lattice systems, YbIr3Ge7 shows magnetic order with moments aligned orthogonal to the crystal electric field (CEF) easy axis. YbIr3Ge7 is unique in that it is the only membe…
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Ferromagnetic Kondo lattice compounds are far less common than their antiferromagnetic analogs. In this work, we report the discovery of a new ferromagnetic Kondo lattice compound, YbIr3Ge7. Like almost all ferromagnetic Kondo lattice systems, YbIr3Ge7 shows magnetic order with moments aligned orthogonal to the crystal electric field (CEF) easy axis. YbIr3Ge7 is unique in that it is the only member of this class of compounds that crystallizes in a rhombohedral structure with a trigonal point symmetry of the magnetic site, and it lacks broken inversion symmetry at the local moment site. AC magnetic susceptibility, magnetization, and specific heat measurements show that YbIr3Ge7 has a Kondo temperature TK = 14 K and a Curie temperature TC = 2.4 K. Ferromagnetic order occurs along the crystallographic [100] hard CEF axis despite the large CEF anisotropy of the ground state Kramers doublet with a saturation moment along [001] almost four times larger than the one along [100]. This implies that a mechanism which considers the anisotropy in the exchange interaction to explain the hard axis ordering is unlikely. On the other hand, the broad second-order phase transition at TC favors a fluctuation-induced mechanism.
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Submitted 8 January, 2019;
originally announced January 2019.
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Crystalline electric field of Ce in trigonal symmetry: CeIr3Ge7 as a model case
Authors:
Jacintha Banda,
Binod K. Rai,
Helge Rosner,
Emilia Morosan,
Christoph Geibel,
Manuel Brando
Abstract:
The crystalline electric field (CEF) of Ce3+ in trigonal symmetry has recently become of some relevance, for instance, in the search of frustrated magnetic systems. Fortunately, it is one of the CEF case in which a manageable analytic solution can be obtained. Here, we present this solution for the general case, and use this result to determine the CEF scheme of the new compound CeIr3Ge7 with the…
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The crystalline electric field (CEF) of Ce3+ in trigonal symmetry has recently become of some relevance, for instance, in the search of frustrated magnetic systems. Fortunately, it is one of the CEF case in which a manageable analytic solution can be obtained. Here, we present this solution for the general case, and use this result to determine the CEF scheme of the new compound CeIr3Ge7 with the help of T-dependent susceptibility and isothermal magnetization measurements. The resulting CEF parameters B20 = 34.4 K, B40 = 0.82 K and B43 = 67.3 K correspond to an exceptional large CEF splittings of the first and second excited levels, 374 K and 1398 K, and a large mixing between the +-|5/2> and the -+|1/2> states. This indicates a very strong easy plane anisotropy with an unusual small c-axis moment. Using the same general expressions, we show that the properties of the recently reported system CeCd3As3 can also be described by a similar CEF scheme, providing a much simpler explanation for its magnetic properties than the initial proposal. Moreover, a similar strong easy plane anisotropy has also been reported for the two compounds CeAuSn and CePdAl4Ge2, indicating that the CEF scheme elaborated here for CeIr3Ge7 corresponds to an exemplary case for Ce3+ in trigonal symmetry.
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Submitted 3 September, 2018; v1 submitted 13 June, 2018;
originally announced June 2018.
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CeIr$_{3}$Ge$_{7}$: a local moment antiferromagnetic metal with extremely low ordering temperature
Authors:
Binod K. Rai,
Jacintha Banda,
Macy Stavinoha,
R. Borth,
D. -J. Jang,
Katherine A. Benavides,
D. A. Sokolov,
Julia Y. Chan,
M. Nicklas,
Manuel Brando,
C. -L. Huang,
E. Morosan
Abstract:
CeIr$_3$Ge$_7$ is an antiferromagnetic metal with a remarkably low ordering temperature $T_{\rm N}$ = 0.63 K, while most Ce-based magnets order between 2 and 15 K. Thermodynamic and transport properties as a function of magnetic field or pressure do not show signatures of Kondo correlations, interaction competition, or frustration, as had been observed in a few antiferromagnets with comparably low…
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CeIr$_3$Ge$_7$ is an antiferromagnetic metal with a remarkably low ordering temperature $T_{\rm N}$ = 0.63 K, while most Ce-based magnets order between 2 and 15 K. Thermodynamic and transport properties as a function of magnetic field or pressure do not show signatures of Kondo correlations, interaction competition, or frustration, as had been observed in a few antiferromagnets with comparably low or lower $T_{\rm N}$. The averaged Weiss temperature measured below 10 K is comparable to $T_{\rm N}$ suggesting that the RKKY exchange coupling is very weak in this material. The unusually low $T_{\rm N}$ in CeIr$_3$Ge$_7$ can therefore be attributed to the large Ce-Ce bond length of about 5.7 Å, which is about 1.5 Å larger than in the most Ce-based intermetallic systems.
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Submitted 13 April, 2018;
originally announced April 2018.