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Nuclear magnetic resonance investigation of the heavy fermion system Ce$_2$CoAl$_7$Ge$_4$
- Source :
- Phys. Rev. B 96, 245132 (2017)
- Publication Year :
- 2018
-
Abstract
- We present nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements performed on single crystalline \ccag{}, a member of a recently discovered family of heavy fermion materials Ce$_2M$Al$_7$Ge$_4$ ($M$ = Co, Ir, Ni, or Pd). Previous measurements indicated a strong Kondo interaction as well as magnetic order below $T_M = 1.8$ K. Our NMR spectral measurements show that the Knight shift $K$ is proportional to the bulk magnetic susceptibility $\chi$ at high temperatures. A clear Knight shift anomaly ($K \not\propto \chi$) is observed at coherence temperatures $T^* \sim 17.5$ K for $H_0 \parallel \hat{c}$ and 10 K for $H_0 \parallel \hat{a}$ at the ${}^{59}$Co site, and $T^* \sim 12.5$ K at the ${}^{27}$Al(3) site for $H_0 \parallel \hat{a}$ characteristic of the heavy fermion nature of this compound. At high temperatures the ${}^{59}$Co NMR spin-lattice relaxation rate $T_1^{-1}$ is dominated by spin fluctuations of the 4$f$ local moments with a weak metallic background. The spin fluctuations probed by ${}^{59}$Co NMR are anisotropic and larger in the basal plane than in the $c$ direction. Furthermore, we find $(T_1TK)^{-1} \propto T^{-1/2}$ at the ${}^{59}$Co site as expected for a Kondo system for $T > T^*$ and $T> T_K$. ${}^{59}$Co NQR \slrr{} measurements at low temperatures indicate slowing down of spin fluctuations above the magnetic ordering temperature $T_M \sim 1.8$ K. A weak ferromagnetic character of fluctuations around $\mathbf{q}=0$ is evidenced by an increase of $\chi T$ versus $T$ above the magnetic ordering temperature. We also find good agreement between the observed and calculated electric field gradients at all observed sites.
- Subjects :
- Condensed Matter - Strongly Correlated Electrons
Subjects
Details
- Database :
- arXiv
- Journal :
- Phys. Rev. B 96, 245132 (2017)
- Publication Type :
- Report
- Accession number :
- edsarx.1812.08633
- Document Type :
- Working Paper
- Full Text :
- https://doi.org/10.1103/PhysRevB.96.245132