Magnetic order and fluctuations in the quasi-two-dimensional planar magnet Sr( Co_1-xNi_x)₂As₂

Journal Article · 23 December 2020 · Physical Review B

DOI: https://doi.org/10.1103/physrevb.102.214431 · OSTI ID:1798602

Xie, Yaofeng  ^[1]; Li, Yu  ^[2]; Yin, Zhiping ^[3]; Zhang, Rui ^[1]; Wang, Weiyi ^[1]; Stone, Matthew B.  ^[4]; Cao, Huibo  ^[4]; Abernathy, D. L.  ^[4]; Harriger, Leland  ^[5]; Young, David P. ^[2]; DiTusa, J. F. ^[2]; Dai, Pengcheng  ^[1]

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1. Rice Univ., Houston, TX (United States)
2. Louisiana State Univ., Baton Rouge, LA (United States)
3. Beijing Normal Univ. (China). Center for Advanced Quantum Studies
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
5. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Center for Neutron Research

We use neutron scattering to investigate spin excitations in $\mathrm{Sr}{\left({\mathrm{Co}}_{1-x}{\mathrm{Ni}}_x\right)}_2{\mathrm{As}}_2$, which has a $c$-axis incommensurate helical structure of the two-dimensional (2D) in-plane ferromagnetic (FM) ordered layers for $0.013\le x\le 0.25$. By comparing the wave vector and energy dependent spin excitations in helical ordered $\mathrm{Sr}{\left({\mathrm{Co}}_{0.9}{\mathrm{Ni}}_{0.1}\right)}_2{\mathrm{As}}_2$ and paramagnetic ${\mathrm{SrCo}}_2{\mathrm{As}}_2$, we find that Ni doping, while increasing lattice disorder in $\mathrm{Sr}{\left({\mathrm{Co}}_{1-x}{\mathrm{Ni}}_x\right)}_2{\mathrm{As}}_2$, enhances quasi-2D FM spin fluctuations. However, our band structure calculations within the combined density functional theory and dynamic mean field theory ( $\mathrm{DFT}+\mathrm{DMFT}$) failed to generate a correct incommensurate wave vector for the observed helical order from nested Fermi surfaces. Furthermore, since transport measurements reveal increased in-plane and $c$-axis electrical resistivity with increasing Ni doping and associated lattice disorder, we conclude that the helical magnetic order in $\mathrm{Sr}{\left({\mathrm{Co}}_{1-x}{\mathrm{Ni}}_x\right)}_2{\mathrm{As}}_2$ may arise from a quantum order-by-disorder mechanism through the itinerant electron mediated Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: Fundamental Research Funds for the Central Universities; National Natural Science Foundation of China (NSFC); National Science Foundation (NSF); Robert A. Welch Foundation; USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC05-00OR22725; SC0012432
• OSTI ID: 1798602
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 21 Vol. 102; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English