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Title: Nuclear magnetic resonance investigation of the heavy fermion system Ce 2 CoAl 7 Ge 4

Abstract

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.

Authors:
 [1];  [2];  [3];  [1];  [1];  [4];  [1];  [1];  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
  4. Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); LANL Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1514954
Alternate Identifier(s):
OSTI ID: 1414622
Report Number(s):
LA-UR-17-25765
Journal ID: ISSN 2469-9950
Grant/Contract Number:  
89233218CNA000001
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 96; Journal Issue: 24; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; strongly correlated systems; nuclear magnetic resonance

Citation Formats

Dioguardi, A. P., Guzman, P., Rosa, P. F. S., Ghimire, N. J., Eley, S., Brown, S. E., Thompson, J. D., Bauer, E. D., and Ronning, F. Nuclear magnetic resonance investigation of the heavy fermion system Ce2CoAl7Ge4. United States: N. p., 2017. Web. doi:10.1103/PhysRevB.96.245132.
Dioguardi, A. P., Guzman, P., Rosa, P. F. S., Ghimire, N. J., Eley, S., Brown, S. E., Thompson, J. D., Bauer, E. D., & Ronning, F. Nuclear magnetic resonance investigation of the heavy fermion system Ce2CoAl7Ge4. United States. doi:10.1103/PhysRevB.96.245132.
Dioguardi, A. P., Guzman, P., Rosa, P. F. S., Ghimire, N. J., Eley, S., Brown, S. E., Thompson, J. D., Bauer, E. D., and Ronning, F. Fri . "Nuclear magnetic resonance investigation of the heavy fermion system Ce2CoAl7Ge4". United States. doi:10.1103/PhysRevB.96.245132. https://www.osti.gov/servlets/purl/1514954.
@article{osti_1514954,
title = {Nuclear magnetic resonance investigation of the heavy fermion system Ce2CoAl7Ge4},
author = {Dioguardi, A. P. and Guzman, P. and Rosa, P. F. S. and Ghimire, N. J. and Eley, S. and Brown, S. E. and Thompson, J. D. and Bauer, E. D. and Ronning, F.},
abstractNote = {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.},
doi = {10.1103/PhysRevB.96.245132},
journal = {Physical Review B},
number = 24,
volume = 96,
place = {United States},
year = {2017},
month = {12}
}

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