Abstract
Whereas magnetic frustration is typically associated with local-moment magnets in special geometric arrangements, here we show that SrCo2As2 is a candidate for frustrated itinerant magnetism. Using inelastic neutron scattering (INS), we find that antiferromagnetic (AF) spin fluctuations develop in the square Co layers of SrCo2As2 below T≈100 K centered at the stripe-type AF propagation vector of (12,12), and that their development is concomitant with a suppression of the uniform magnetic susceptibility determined via magnetization measurements. We interpret this switch in spectral weight as signaling a temperature-induced crossover from an instability toward ferromagnetism ordering to an instability toward stripe-type AF ordering on cooling, and show results from Monte-Carlo simulations for a J1-J2 Heisenberg model that illustrates how the crossover develops as a function of the frustration ratio -J1/(2J2). By putting our INS data on an absolute scale, we quantitatively compare them and our magnetization data to exact-diagonalization calculations for the J1-J2 model [N. Shannon, Eur. Phys. J. B 38, 599 (2004).EPJBFY1434-602810.1140/epjb/e2004-00156-3], and show that the calculations predict a lower level of magnetic frustration than indicated by experiment. We trace this discrepancy to the large energy scale of the fluctuations (Javg 75 meV), which, in addition to the steep dispersion, is more characteristic of itinerant magnetism.
Original language | English |
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Article number | 054411 |
Journal | Physical Review B |
Volume | 100 |
Issue number | 5 |
DOIs | |
State | Published - Aug 9 2019 |
Funding
We interpret the suppression of χ ( 0 , 0 ) and rise in χ ( Q stripe , 0 ) below T max as signaling a crossover from predominantly FM to predominately stripe-type AF fluctuations. These fluctuations are presumably associated with corresponding FM and AF phases that lie close in energy. This is supported by the following facts. First, the magnitude of χ ( 0 , 0 ) at high temperature, the positive Weiss temperature, and the large Stoner parameter of I D ( E F ) = 2.2 found in Ref. [20] are all consistent with a Stoner FM instability. Second, NMR and INS results both show evidence for FM fluctuations being present [25,42] . Third, Fig. 10 clearly shows that the leading magnetic instability, determined by the maximum in χ ′ ( Q , 0 ) , crosses over from Q = 0 to Q stripe with decreasing temperature.