Nuclear magnetic resonance investigation of the heavy fermion system
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
- Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy
We present here nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements performed on single crystalline $${\mathrm{Ce}}_{2}{\mathrm{CoAl}}_{7}{\mathrm{Ge}}_{4}$$, a member of a recently discovered family of heavy fermion materials $${\mathrm{Ce}}_{2}M{\mathrm{Al}}_{7}{\mathrm{Ge}}_{4}$$ ($$M=\mathrm{Co}$$, Ir, Ni, or Pd). Previous measurements indicated a strong Kondo interaction as well as magnetic order below $${T}_{M}=1.8\mathrm{K}$$. 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 ($$K\neg{}{\propto}{\chi}$$) is observed at coherence temperatures $${T}^{*}{\sim}17.5\mathrm{K}$$ for $${H}_{0}{\parallel}\stackrel{\hat{}{}{}}{c}$$ and 10 K for $${H}_{0}{\parallel}\stackrel{\hat{}{}{}}{a}$$ at the $$^{59}\mathrm{Co}$$ site, and $${T}^{*}{\sim}12.5\mathrm{K}$$ at the $$^{27}\mathrm{Al}$$(3) site for $${H}_{0}{\parallel}\stackrel{\hat{}{}{}}{a}$$ characteristic of the heavy fermion nature of this compound. At high temperatures, the $$^{59}\mathrm{Co}$$ NMR spin-lattice relaxation rate $${T}_{1}^{{-}1}$$ is dominated by spin fluctuations of the $4f$ local moments with a weak metallic background. The spin fluctuations probed by $$^{59}\mathrm{Co}$$ NMR are anisotropic and larger in the basal plane than in the $$c$$ direction. Furthermore, we find $${({T}_{1}TK)}^{{-}1}{\propto}{T}^{{-}1/2}$$ at the $$^{59}\mathrm{Co}$$ site as expected for a Kondo system for $$T>{T}^{*}$$ and $$T>{T}_{K}$$. $$^{59}\mathrm{Co}$$ NQR $${T}_{1}^{{-}1}$$ measurements at low temperatures indicate slowing down of spin fluctuations above the magnetic ordering temperature $${T}_{M}{\sim}1.8\mathrm{K}$$. 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.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); LANL Laboratory Directed Research and Development (LDRD) Program
- Grant/Contract Number:
- 89233218CNA000001
- OSTI ID:
- 1514954
- Alternate ID(s):
- OSTI ID: 1414622
- Report Number(s):
- LA-UR-17-25765
- Journal Information:
- Physical Review B, Vol. 96, Issue 24; ISSN 2469-9950
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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