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Evolution of Bonding and Magnetism via Changes in Valence Electron Count in CuFe2–xCoxGe2

Journal Article · · Inorganic Chemistry
 [1];  [1];  [2];  [3];  [4];  [4];  [5];  [6]
  1. Florida State Univ., Tallahassee, FL (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Argonne National Lab. (ANL), Lemont, IL (United States)
  4. Ames Lab., and Iowa State Univ., Ames, IA (United States)
  5. Univ. of Idaho, Moscow, ID (United States)
  6. Florida State Univ., Tallahassee, FL (United States); Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab. (MagLab)
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A series of solid solutions, CuFe2–xCoxGe2 (x = 0, 0.2, 0.4, 0.8, and 1.0), have been synthesized by arc-melting and characterized by powder X-ray and neutron diffraction, magnetic measurements, Mössbauer spectroscopy, and electronic band structure calculations. All compounds crystallize in the CuFe2Ge2 structure type, which can be considered as a three-dimensional framework built of fused MGe6 octahedra and MGe5 trigonal bipyramids (M = Fe and Co), with channels filled by rows of Cu atoms. As the Co content (x) increases, the unit cell volume decreases in an anisotropic fashion: the b and c lattice parameters decrease while the a parameter increases. The changes in all the parameters are nearly linear, thus following Vegard’s law. CuFe2Ge2 exhibits two successive antiferromagnetic (AFM) orderings, corresponding to the formation of a commensurate AFM structure, followed by an incommensurate AFM structure observed at lower temperatures. Additionally, as the Co content increases, the AFM ordering temperature (TN) gradually decreases, and only one AFM transition is observed for x ≥ 0.2. The magnetic behavior of unsubstituted CuFe2Ge2 was found to be sensitive to the preparation method. The temperature-dependent zero-field 57Fe Mössbauer spectra reveal two hyperfine split components that evolve in agreement with the two consecutive AFM orderings observed in magnetic measurements. In contrast, the field-dependent spectra obtained for fields ≥ 2 T reveal a parallel arrangement of the moments associated with the two crystallographically unique metal sites. Electronic band structure calculations and chemical bonding analysis reveal a mix of strong M–M antibonding and non-bonding states at the Fermi level, in support of the overall AFM ordering observed in zero field. The substitution of Co for Fe reduces the population of the M–M antibonding states and the overall density of states at the Fermi level, thus suppressing the TN value.
Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
National Science Foundation (NSF); Swiss National Science Foundation (SNSF); USDOE Office of Science (SC); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division; University of Idaho
Grant/Contract Number:
AC02-06CH11357; AC02-07CH11358; AC05-00OR22725
OSTI ID:
1863299
Alternate ID(s):
OSTI ID: 1894692
Journal Information:
Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 10 Vol. 61; ISSN 0020-1669
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
annealing (metallurgy)
chemical structure
diffraction
magnetic properties
materials