arXiv subjects

M. Deppe

Publications and source records attributed to M. Deppe.

5 recordsLinked to original sources

arXiv2022

Neutron Depolarization due to Ferromagnetism and Spin Freezing in CePd$_{1-x}$Rh$_x$

We report neutron depolarization measurements of the suppression of long-range ferromagnetism and the emergence of magnetic irreversibilities and spin freezing in CePd$_{1-x}$Rh$_x$ around $x^*\approx0.6$. Tracking the temperature versus field history of the neutron depolarization, we find clear signatures of long-range Ising ferromagnetism below a Curie temperature $T_{\rm C}$ for $x=0.4$ and a spin freezing of tiny ferromagnetic clusters below a freezing temperature $T_{\rm F1}$ for $x>x^*$. Under zero-field-cooling/field-heating and for $x>x^*$ a reentrant temperature dependence of the neutron depolarization between $T_{\rm F2}<T_{\rm F1}$ and $T_{\rm F1}$ is microscopically consistent with a thermally activated growth of the cluster size. The evolution of the depolarization as well as the reentrant temperature dependence as a function of Rh content are consistent with the formation of a Kondo-cluster glass below $T_{\rm F1}$ adjacent to a ferromagnetic quantum phase transition at $x^*$.

cond-mat.str-el↗

arXiv2009

Quantum Griffiths phase in CePd(1-x)Rh(x) with x ~ 0.8

The magnetic field dependence of the magnetisation ($M$) and the temperature dependence of the ac susceptibility ($χ' = dM/dH$) of CePd(1-x)Rh(x) single crystals with $0.80 \leq x \leq 0.86$ are analysed within the frame of the quantum Griffiths phase scenario, which predicts $M \propto H^λ$ and $χ' \propto T^{λ-1}$ with $0 \leq λ\leq 1$. All $M$ vs $H$ and $χ'$ vs $T$ data follow the predicted power-law behaviour. The parameter $λ$, extracted from $χ'(T)$, is very sensitive to the Rh content $x$ and varies systematically with $x$ from -0.1 to 0.4. The value of $λ$, derived from $M(H)$ measurements on a \cpr single crystal, seems to be rather constant, $λ\approx 0.2$, in a broad range of temperatures between 0.05 and 2 K and fields up to about 10 T. All observed signatures and the $λ$ values are thus compatible with the quantum Griffiths scenario.

cond-mat.str-el↗

arXiv2009

Kondo-Cluster-Glass State near a Ferromagnetic Quantum Phase Transition

We report on a comprehensive study of CePd$_{1-x}$Rh$_x$ $(0.6 \leq x \leq 0.95)$ poly- and single crystals close to the ferromagnetic instability by means of low-temperature ac susceptibility, magnetization and volume thermal expansion. The signature of ferromagnetism in this heavy-fermion system can be traced from 6.6 K in CePd down to 25 mK for $x=0.87$. Despite pronounced non-Fermi-liquid (NFL) effects in both, specific heat and thermal expansion, the Grüneisen ratio {\it does not} diverge as $T\to 0$, providing evidence for the absence of a quantum critical point. Instead, a peculiar "Kondo-cluster-glass" state is found for $x\geq 0.65$, and the NFL effects in the specific heat, ac susceptibility and magnetization are compatible with the quantum Griffiths phase scenario.

cond-mat.str-el↗

arXiv2005

Non-Fermi liquid states in the pressurized $CeCu_2(Si_{1-x}Ge_x)_2$ system: two critical points

In the archetypal strongly correlated electron superconductor CeCu$_2$Si$_2$ and its Ge-substituted alloys CeCu$_2$(Si$_{1-x}$Ge$_{x}$)$_2$ two quantum phase transitions -- one magnetic and one of so far unknown origin -- can be crossed as a function of pressure \cite{Yuan 2003a}. We examine the associated anomalous normal state by detailed measurements of the low temperature resistivity ($ρ$) power law exponent $α$. At the lower critical point (at $p_{c1}$, $1\leqα\leq 1.5$) $α$ depends strongly on Ge concentration $x$ and thereby on disorder level, consistent with a Hlubina-Rice-Rosch scenario of critical scattering off antiferromagnetic fluctuations. By contrast, $α$ is independent of $x$ at the upper quantum phase transition (at $p_{c2}$, $α\simeq 1$), suggesting critical scattering from local or Q=0 modes, in agreement with a density/valence fluctuation approach.

cond-mat.str-el↗

arXiv2004

Low temperature magnetic phase diagram of the cubic non-Fermi liquid system CeIn_(3-x)Sn_x

In this paper we report a comprehensive study of the magnetic susceptibility (χ), resistivity (ρ), and specific heat (C_P), down to 0.5 K of the cubic CeIn_(3-x)Sn_x alloy. The ground state of this system evolves from antiferromagnetic (AF) in CeIn_3(T_N=10.2 K) to intermediate-valent in CeSn_3, and represents the first example of a Ce-lattice cubic non-Fermi liquid (NFL) system where T_N(x) can be traced down to T=0 over more than a decade of temperature. Our results indicate that the disappearance of the AF state occurs near x_c ~ 0.7, although already at x ~ 0.4 significant modifications of the magnetic ground state are observed. Between these concentrations, clear NFL signatures are observed, such as ρ(T)\approx ρ_0 + A T^n (with n<1.5) and C_P(T)\propto -T ln(T) dependencies. Within the ordered phase a first order phase transition occurs for 0.25 < x < 0.5. With larger Sn doping, different weak ρ(T) dependencies are observed at low temperatures between x=1 and x=3 while C_P/T shows only a weak temperature dependence.

cond-mat.str-el↗