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Title: Non-Fermi-liquid types of behavior associated with a magnetic quantum critical point in Sr ( Co 1 - x Ni x ) 2 As 2 single crystals

Abstract

The compound SrCo 2As 2 with the body-centered tetragonal ThCr 2Si 2 structure is known to remain paramagnetic down to a temperature T = 0.05 K, but inelastic neutron scattering studies have shown that both ferromagnetic (FM) and antiferromagnetic (AFM) fluctuations occur in single crystals. Thus it is of interest to study how the magnetism evolves on doping SrCo 2As 2. Previous work on polycrystalline samples of Sr (Co 1-x Ni x) 2 As 2 indicated the development of AFM order for 0 < x ≲ 0.3. Here we studied single crystals of Sr(Co 1-x Ni x) 2 As 2 for 0 < x ≤ 1 and confirmed the occurrence of AFM order which we deduce to have a c -axis helix structure. We also find evidence for an unusual composition-induced magnetic quantum critical point at x ≈ 0.3 where non-Fermi-liquid types of behavior were revealed by heat capacity and electrical resisitivity measurements at low T. Electron-doped Sr (Co 1-x Ni x) 2 As 2 single crystals with compositions x = 0 to 0.9 were grown out of self-flux and SrNi 2 As 2 single crystals out of Bi flux. The crystals were characterized using single-crystal x-ray diffraction (XRD) atmore » room temperature, and magnetic susceptibility χ (H, T), isothermal magnetization M (H, T), heat capacity Cp (H, T), and electrical resistivity ρ (H, T) measurements versus applied magnetic field H and T. The XRD studies show that the system undergoes a continuous structural crossover from the uncollapsed-tetragonal (ucT) structure to the collapsed tetragonal (cT) structure with increasing Ni doping. The χ(T) data show that SrCo 2As 2 exhibits an AFM ground state almost immediately upon Ni doping on the Co site. Ab initio electronic-structure calculations for x = 0 and 0.15 indicate that a flat band with a peak in the density of states just above the Fermi energy is responsible for this initial magnetic-ordering behavior on Ni doping. The AFM ordering is observed in the range 0.013 ≤ x ≤ 0.25 with the ordered moments aligned in the ab plane and with a maximum ordering temperature T N = 26.5 K at x = 0.10. The Curie-Weiss-like T dependence of χ in the paramagnetic (PM) state indicates dominant FM interactions. The behavior of the anisotropic susceptibilities below T N suggests a planar helical magnetic ground state with a composition-dependent pitch based on a local-moment molecular-field-theory model, with FM interactions in the ab plane and weaker AFM interactions along the helix c axis. However, the small ordered (saturation) moments ~0.1 μ B per transition metal atom, where μ B is the Bohr magneton, and the values of the Rhodes-Wohlfarth ratio indicate that the magnetism is itinerant. The high-field M (H) isotherms and the low-field χ-1 ( T > T N) data were successfully analyzed within the framework of Takahashi's theory of FM spin fluctuations. The C p (T) at low T exhibits Fermi-liquid behavior for 0 ≤ x ≤ 0.15 , whereas an evolution to a logarithmic non-Fermi-liquid (NFL) behavior is found for x = 0.2 to 0.3. The logarithmic dependence is suppressed in an applied magnetic field. The low- T ρ ( H = 0 , T ) data show a T 2 dependence for 0 ≤ x ≤ 0.20 and a power-law dependence ρ (H = 0, T) = ρ 0 + AT n with n < 2 for x = 0.20 and 0.30. The exponent n shows a notable field dependence, suggesting both doping- and magnetic-field-tuned quantum critical phenomena. These low- T NFL types of behavior observed in the C p and ρ measurements are most evident near the quantum critical concentration x ≈ 0.3 at which a T = 0 composition-induced transition from the AFM phase to the PM phase occurs.« less

Authors:
 [1];  [1];  [1]; ORCiD logo [2]; ORCiD logo [2]; ORCiD logo [3];  [4];  [4]; ORCiD logo [4]
  1. Ames Lab., and Iowa State Univ., Ames, IA (United States)
  2. Stockholm Univ. (Sweden)
  3. Iowa State Univ., Ames, IA (United States). Dept. of Materials Science & Engineering
  4. Ames Lab., and Iowa State Univ., Ames, IA (United States). Dept. of Physics and Astronomy
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division
OSTI Identifier:
1570834
Report Number(s):
IS-J-10060
Journal ID: ISSN 2469-9950; PRBMDO
Grant/Contract Number:  
AC02-07CH11358
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 100; Journal Issue: 9; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Sangeetha, N. S., Wang, L. -L., Smirnov, A. V., Smetana, V., Mudring, A. -V., Johnson, D. D., Tanatar, M. A., Prozorov, R., and Johnston, D. C. Non-Fermi-liquid types of behavior associated with a magnetic quantum critical point in Sr(Co1-xNix)2As2 single crystals. United States: N. p., 2019. Web. doi:10.1103/PhysRevB.100.094447.
Sangeetha, N. S., Wang, L. -L., Smirnov, A. V., Smetana, V., Mudring, A. -V., Johnson, D. D., Tanatar, M. A., Prozorov, R., & Johnston, D. C. Non-Fermi-liquid types of behavior associated with a magnetic quantum critical point in Sr(Co1-xNix)2As2 single crystals. United States. doi:10.1103/PhysRevB.100.094447.
Sangeetha, N. S., Wang, L. -L., Smirnov, A. V., Smetana, V., Mudring, A. -V., Johnson, D. D., Tanatar, M. A., Prozorov, R., and Johnston, D. C. Mon . "Non-Fermi-liquid types of behavior associated with a magnetic quantum critical point in Sr(Co1-xNix)2As2 single crystals". United States. doi:10.1103/PhysRevB.100.094447. https://www.osti.gov/servlets/purl/1570834.
@article{osti_1570834,
title = {Non-Fermi-liquid types of behavior associated with a magnetic quantum critical point in Sr(Co1-xNix)2As2 single crystals},
author = {Sangeetha, N. S. and Wang, L. -L. and Smirnov, A. V. and Smetana, V. and Mudring, A. -V. and Johnson, D. D. and Tanatar, M. A. and Prozorov, R. and Johnston, D. C.},
abstractNote = {The compound SrCo2As2 with the body-centered tetragonal ThCr2Si2 structure is known to remain paramagnetic down to a temperature T = 0.05 K, but inelastic neutron scattering studies have shown that both ferromagnetic (FM) and antiferromagnetic (AFM) fluctuations occur in single crystals. Thus it is of interest to study how the magnetism evolves on doping SrCo2As2. Previous work on polycrystalline samples of Sr (Co1-x Nix)2 As2 indicated the development of AFM order for 0 < x ≲ 0.3. Here we studied single crystals of Sr(Co1-x Nix)2 As2 for 0 < x ≤ 1 and confirmed the occurrence of AFM order which we deduce to have a c -axis helix structure. We also find evidence for an unusual composition-induced magnetic quantum critical point at x ≈ 0.3 where non-Fermi-liquid types of behavior were revealed by heat capacity and electrical resisitivity measurements at low T. Electron-doped Sr (Co1-x Nix)2 As2 single crystals with compositions x = 0 to 0.9 were grown out of self-flux and SrNi2 As2 single crystals out of Bi flux. The crystals were characterized using single-crystal x-ray diffraction (XRD) at room temperature, and magnetic susceptibility χ (H, T), isothermal magnetization M (H, T), heat capacity Cp (H, T), and electrical resistivity ρ (H, T) measurements versus applied magnetic field H and T. The XRD studies show that the system undergoes a continuous structural crossover from the uncollapsed-tetragonal (ucT) structure to the collapsed tetragonal (cT) structure with increasing Ni doping. The χ(T) data show that SrCo2As2 exhibits an AFM ground state almost immediately upon Ni doping on the Co site. Ab initio electronic-structure calculations for x = 0 and 0.15 indicate that a flat band with a peak in the density of states just above the Fermi energy is responsible for this initial magnetic-ordering behavior on Ni doping. The AFM ordering is observed in the range 0.013 ≤ x ≤ 0.25 with the ordered moments aligned in the ab plane and with a maximum ordering temperature TN = 26.5 K at x = 0.10. The Curie-Weiss-like T dependence of χ in the paramagnetic (PM) state indicates dominant FM interactions. The behavior of the anisotropic susceptibilities below TN suggests a planar helical magnetic ground state with a composition-dependent pitch based on a local-moment molecular-field-theory model, with FM interactions in the ab plane and weaker AFM interactions along the helix c axis. However, the small ordered (saturation) moments ~0.1 μB per transition metal atom, where μB is the Bohr magneton, and the values of the Rhodes-Wohlfarth ratio indicate that the magnetism is itinerant. The high-field M (H) isotherms and the low-field χ-1 ( T > TN) data were successfully analyzed within the framework of Takahashi's theory of FM spin fluctuations. The Cp (T) at low T exhibits Fermi-liquid behavior for 0 ≤ x ≤ 0.15 , whereas an evolution to a logarithmic non-Fermi-liquid (NFL) behavior is found for x = 0.2 to 0.3. The logarithmic dependence is suppressed in an applied magnetic field. The low- T ρ ( H = 0 , T ) data show a T2 dependence for 0 ≤ x ≤ 0.20 and a power-law dependence ρ (H = 0, T) = ρ0 + ATn with n < 2 for x = 0.20 and 0.30. The exponent n shows a notable field dependence, suggesting both doping- and magnetic-field-tuned quantum critical phenomena. These low- T NFL types of behavior observed in the Cp and ρ measurements are most evident near the quantum critical concentration x ≈ 0.3 at which a T = 0 composition-induced transition from the AFM phase to the PM phase occurs.},
doi = {10.1103/PhysRevB.100.094447},
journal = {Physical Review B},
issn = {2469-9950},
number = 9,
volume = 100,
place = {United States},
year = {2019},
month = {9}
}

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