Magnetic states of the Kondo lattice Ce$_2$PdSi$_3$ and their pressure evolution

TL;DR

Ce2PdSi3 is studied as a frustrated Ce-based Kondo lattice to understand how magnetic order evolves under hydrostatic pressure and magnetic field. Using single-crystal measurements of resistivity, magnetic susceptibility, heat capacity, and neutron diffraction up to 7.5 GPa, the authors identify two ambient-pressure magnetic transitions: a ferromagnetic-like transition at $T_{ m M1}=3.8$ K and an incommensurate antiferromagnetic transition at $T_{ m M2}=2.9$ K, with neutron data showing $k_1=oldsymbol{0}$ and $k_2=(0.15,0,0)$. Under pressure, $T_{ m M1}$ is suppressed to zero near $P=4.2$ GPa while $T_{ m M2}$ increases to at least $7.5$ GPa; a further low-temperature anomaly $T'$ appears near $2.4$ K around $P>4.2$ GPa, indicating a possible change in magnetic structure. The results reveal competing magnetic orders and a non-Didonch-type pressure evolution, suggesting a role for geometric frustration beyond the standard Doniach framework and motivating investigation of potential topological spin textures in the high-pressure regime.

Abstract

Frustrated Kondo lattices are ideal platforms for exploring unconventional forms of quantum criticality, as well as magnetism and other emergent phases. Here we report the magnetic properties of the candidate frustrated heavy fermion compound Ce$_2$PdSi$_3$, and map their evolution upon applying magnetic fields and hydrostatic pressure. We find that at ambient pressure Ce$_2$PdSi$_3$ exhibits two distinct magnetic phase transitions, a ferromagnetic-like transition at $T_{\mathrm{M1}}=3.8$ K and an incommensurate antiferromagnetic transition at $T_{\mathrm{M2}}=2.9$ K. Upon applying pressure, $T_{\mathrm{M1}}$ is continuously suppressed and becomes undetectable above 4.2 GPa, whereas $T_{\mathrm{M2}}$ increases and remains robust up to at least 7.5 GPa. The observed pressure evolution of magnetic order in Ce$_2$PdSi$_3$ suggests the presence of competing magnetic orders, and cannot be simply encapsulated by the Doniach phase diagram, motivating further investigations for its origin, including discerning the role of geometric frustration.

Figures (5)

• Figure 1: (Color online) (a) Temperature dependence of the electrical resistivity $\rho(T)$ of Ce$_2$PdSi$_3$ at ambient pressure from 300 to 2 K. The inset displays the low temperature resistivity curves measured under various magnetic fields applied along the $c$ direction, where the trend of the magnetic transition $T_{\mathrm{M1}}$ is shown. (b) Low-temperature magnetic susceptibility $\chi(T)$ for $\mu_0 H = 0.1$ T with $H \parallel c$. The ZFC curve (red) was recorded on warming after cooling in zero field, whereas the FC curve (black) was recorded during field cooling from base temperature (2 K). (c) Isothermal magnetization $M(H)$ for $H \parallel ab$ at representative temperatures below and above $T_{\mathrm{M1}}$. (d) Specific heat plotted as $C_p(T)$ versus $T$ under various magnetic fields applied along the $c$ direction.
• Figure 2: (Color online) (a)–(c) Neutron diffraction intensity patterns of Ce$_2$PdSi$_3$ collected in the $(H,\,0.5,\,L)$ scattering plane at 8 K, 3.4 K, and 1.6 K, respectively. Magnetic Bragg peaks corresponding to the ferromagnetic and antiferromagnetic orders are highlighted by red and blue circles, respectively.
• Figure 3: (Color online) Temperature dependence of the ac heat-capacity coefficient $C_{\mathrm{ac}}(T)/T$ of Ce$_2$PdSi$_3$ measured at pressures between 1.3 and 7.5 GPa. Black (orange) arrows mark the trend of the FM (AFM) transitions. Note that the curves are vertically shifted for clarity.
• Figure 4: (Color online) (a) Low-temperature resistivity $\rho(T)$ of Ce$_2$PdSi$_3$ measured at various pressures between 1.2 and 5.3 GPa. (b) Temperature dependence of the derivative of the resistivity $d\rho/dT$ under pressure. The positions of the transitions are labelled. (c) $\rho(T)$, and (d) $d\rho/dT$ at 4.6 GPa under various applied magnetic fields. Black, purple, and orange arrows mark the transition temperatures $T_{C}$, $T'$, and $T_{N}$, respectively. Note that the curves in panels (c) and (d) are vertically shifted for clarity.
• Figure 5: (Color online) Temperature–pressure phase diagram of Ce$_2$PdSi$_3$ in zero applied magnetic field. Blue, purple, and orange symbols denote $T_{\mathrm{M1}}$, $T'$, and $T_{\mathrm{M2}}$, respectively.