CePdIn Heavy-Fermion Compound Analysis

• CePdIn is a heavy-fermion compound characterized by a geometrically frustrated kagome network, leading to competing Kondo and RKKY interactions.
• Experimental studies using magnetization, heat capacity, and resistivity techniques map its dual antiferromagnetic phases and reveal pressure-tuned quantum transitions.
• Its phase diagram, modulated by magnetic field and hydrostatic pressure, exemplifies a modified Doniach scenario transitioning from localized to itinerant magnetism.

CePdIn is a geometrically frustrated heavy-fermion antiferromagnet that belongs to the ZrNiAl-type structural family (space group P-6 2 m). In this Kondo lattice system, competition between the Kondo effect, Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange, and geometric frustration produces a rich phase diagram with two distinct antiferromagnetic ground states, whose stability can be tuned via applied magnetic field and hydrostatic pressure. The structural, electronic, and magnetic properties of CePdIn epitomize the interplay between magnetic ordering, quantum fluctuations, and Kondo hybridization in partially frustrated rare-earth intermetallics (Shen et al., 27 Dec 2025).

1. Crystal Structure, Magnetic Lattice, and Frustration

CePdIn crystallizes in the hexagonal ZrNiAl-type structure, with Ce ions occupying the vertices of a slightly distorted two-dimensional kagome network in the basal (ab-) plane and stacking along the c-axis. Each Ce atom has six in-plane nearest neighbors (NN, interatomic distance ≈ 4.45 Å) forming kagome triangles, and three neighbors along the c-axis (out-of-plane separation c ≈ 4.08 Å), imparting more three-dimensionality compared to its more anisotropic cousin CePdAl (c/a ≈ 0.59). The resulting topology generates nearly degenerate NN and next-nearest-neighbor (NNN) RKKY exchange paths, thereby inducing magnetic frustration and suppressing simple Néel ordering. The frustrated connectivity reduces the ordered moment and enhances low-energy quantum fluctuations, affecting the nature of magnetic ground states (Shen et al., 27 Dec 2025).

2. Experimental Methodologies for Probing CePdIn

Single crystals of CePdIn are synthesized using the Czochralski method in a tetra-arc furnace. Magnetic, thermal, and transport properties are interrogated through:

• Magnetization M(H,T) measurements with a Quantum Design MPMS down to 0.1 K (using both ^3He and dilution refrigerator inserts), for fields applied both parallel and perpendicular to the c-axis.
• Heat capacity C(T,H) via relaxation calorimetry in a PPMS with ^3He insert (to 0.4 K), and with ac-calorimetry up to 5 GPa (0.3–10 K) using piston-cylinder and diamond anvil cells (DAC).
• Electrical resistivity ρ(T,H,P) measured via a four-probe method in both ^3He cryostats (0.3–4 K, up to 9 T) and DACs (0.3–300 K, up to 8 T, up to 6.3 GPa). Pressure media and calibration are maintained with Daphne 7373 and ruby fluorescence, respectively. This suite of techniques enables full mapping of field–temperature and pressure–temperature phase diagrams and tracking of magnetic order from ambient through multi-GPa regimes (Shen et al., 27 Dec 2025).

3. Magnetic Transitions and Tuning by Field and Pressure

At ambient pressure, CePdIn exhibits two stepwise antiferromagnetic transitions:

• $T_{\rm N}(0) \simeq 1.65\,\textrm{K}$ (primary Néel temperature)
• $T_{\rm M}(0) \simeq 1.15\,\textrm{K}$ (secondary anomaly)

Both transitions are evident as sharp anomalies in heat capacity and resistivity. Applied magnetic fields along the c-axis monotonically suppress $T_{\rm N}$ and $T_{\rm M}$, with both collapsing above a critical field $\mu_0 H_c \simeq 6\,\rm T$, where a Schottky-like anomaly in $C/T$ evidences Zeeman splitting of the crystal electric field (CEF) doublet.

Pressure evolution of $T_{\rm N}(P)$ is highly nonmonotonic:

• $0 < P \lesssim 2.3\,\rm GPa$: $T_{\rm N}(P)$ decreases from 1.65 K to $\sim 0.8$ K.
• $P_c \approxeq 2.6\,\rm GPa$: abrupt rise of $T_{\rm N}$ to $\simeq 1.5$ K.
• $2.6\,\rm GPa < P \lesssim 5\,\rm GPa$: $T_{\rm N}$ weakly pressure dependent, then vanishes suddenly ($P\gtrsim 5\,\rm GPa$).

This can be succinctly approximated as

$$T_{\rm N}(P) \approx \begin{cases} 1.65 - 0.35\,P\ \textrm{(K/GPa)}, & P < 2.3\,\rm GPa \ 1.5\,\textrm{K}, & 2.6 < P < 4.7\,\rm GPa \ 0, & P > 5\,\rm GPa \end{cases}$$

The lower-temperature transition $T_M$ is not clearly resolved under pressure, presumably due to broadening and weakening as quantum fluctuations gain strength (Shen et al., 27 Dec 2025).

4. Dual Antiferromagnetic Phases: AF$_1$ and AF$_2$

The first-order-like jump in $T_{\rm N}$ at $P_c \simeq 2.6\,\rm GPa$ signals a boundary between two antiferromagnetic phases:

• AF$_1$-phase ($P < 2.6\,\rm GPa$): Characterized by a $T_{\rm N}$ rapidly suppressed by field ($\mu_0 H_c \sim 6\,\rm T$), weakly negative magnetoresistance at low $T$, and a metamagnetic kink (∼4 T) that typifies local-moment antiferromagnetism with modest Kondo screening.
• AF$_2$-phase ($P > 2.6\,\rm GPa$): $T_{\rm N}$ notably robust against field (detectable to 8 T). In this regime, low-temperature resistivity increases below $T_{\rm N}$, indicating opening of a partial spin-density-wave gap and increased $f$-electron itinerancy. Magnetoresistance remains positive throughout accessible fields.

The AF$_1$–AF$_2$ boundary is tracked via peaks in $d\rho/dT(T)$ and $ac$-$C(T)$ at $T_{\rm N}(P)$. The transition reflects a pressure-induced crossover in Kondo coupling $J_K$ and the single-ion Kondo scale,

$T_K(P) \sim D\,\exp[-1/(J_K(P)\,N_0)]$

with $N_0$ as the conduction electron density of states and $D$ the conduction bandwidth. As $P\to 2.6\,\rm GPa$, $T_K$ approaches the CEF splitting scale ($\sim 70\,\rm K$), evidenced by merging of two resistivity maxima ($T_\mathrm{max1}$, $T_\mathrm{max2}$) for $P > 6.3\,\rm GPa$. The abrupt increase in hybridization reorganizes the magnetic ground state from localized (AF$_1$) to itinerant (AF$_2$) order (Shen et al., 27 Dec 2025).

5. Phase Diagrams and Magnetic Field/Pressure Response

The field–temperature and pressure–temperature diagrams elucidate tunability:

Regime	$T_{\rm N}(P)$ Evolution	AF Phase	Field Response
$P < 2.3$ GPa	Decreases linearly	AF$_1$	$T_{\rm N}$ suppressed, vanishes at 6 T
$2.6 < P < 4.7$ GPa	$\sim$1.5 K plateau	AF$_2$	$T_{\rm N}$ robust to 8 T
$P > 5$ GPa	Collapses to 0	Paramagnetic	No AF order

In the $H$–$T$ plane for $H\parallel c$, both $T_{\rm N}(H)$ and $T_{\rm M}(H)$ are suppressed to zero near 6 T, above which a polarized paramagnetic heavy Fermi-liquid state with $\rho = \rho_0 + AT^2$ is recovered. In the $P$–$T$ phase diagram, AF$_1$ is realized for $P < 2.6$ GPa, AF$_2$ for $2.6 < P < 5$ GPa, and at yet higher $P$ the system enters a nonmagnetic, fully itinerant regime marked by the merging of Kondo coherence peaks ($T_\mathrm{max1}$/$T_\mathrm{max2}$).

6. Specific-Heat and Effective-Mass Signatures

Above $T_{\rm N}$, the specific heat coefficient follows $C/T = \gamma + \beta T^2$ with $\gamma \simeq 121\,\rm mJ\,mol^{-1}\,K^{-2}$ (contrasted with LaPdIn: $\gamma \simeq 11\,\rm mJ\,mol^{-1}\,K^{-2}$), indicating moderately heavy quasiparticles. Near $T_{\rm N}$, the magnetic contribution $C_m/T$ reaches $\sim 1.4\,\rm J\,mol^{-1}\,K^{-2}$ as $T\to 0$, emphasizing dominant spin fluctuations. In the field-polarized regime ($H>H_c$), $\gamma$ is reduced with no observable divergence; no explicit pressure dependence $\gamma(P)$ is reported, but increased itinerancy in AF$_2$ suggests a modest reduction of the effective mass relative to AF$_1$ (Shen et al., 27 Dec 2025).

7. Quantum Criticality and Comparison to Related Systems

CePdIn lacks the extended quantum critical regime and non-Fermi-liquid (NFL) behavior typical of more frustrated ZrNiAl-type systems such as CePdAl, where multi-step metamagnetism and partial moment order are observed. The absence of divergent $C/T$ and non-quadratic resistivity ($\rho \sim T^n$ with $n<2$) near field- and pressure-induced transitions demonstrates that both the $H$- and $P$-tuned boundaries are weakly first-order, preempting quantum criticality. The “modified Doniach scenario” inferred here proceeds from local-moment AF$_1$, through re-entrant itinerant AF$_2$ (pressure-stabilized by Kondo hybridization), to a paramagnetic Fermi-liquid above $P\sim5$ GPa. Modest kagome-like frustration, together with more three-dimensional lattice geometry, limits the emergence of competing or fractionalized phases; subtle changes in crystallographic anisotropy thus markedly modify the interplay of RKKY exchange, Kondo screening, and quantum fluctuations in CePdIn and related materials (Shen et al., 27 Dec 2025).