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

Abstract

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.

Authors:

Xie, Yaofeng  ^[1];

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Li, Yu  ^[2];

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Yin, Zhiping ^[3]; Zhang, Rui ^[1]; Wang, Weiyi ^[1]; Stone, Matthew B.  ^[4];

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Cao, Huibo  ^[4];

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Abernathy, D. L.  ^[4];

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Harriger, Leland  ^[5];

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Young, David P. ^[2]; DiTusa, J. F. ^[2]; Dai, Pengcheng  ^[1]

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• Search DOE PAGES for ORCID "0000-0002-6088-3170"

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+ Show Author Affiliations

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

Publication Date:

Thu Dec 24 00:00:00 EST 2020

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); Robert A. Welch Foundation; National Natural Science Foundation of China (NSFC); Fundamental Research Funds for the Central Universities

OSTI Identifier:

1798602

Grant/Contract Number:  

AC05-00OR22725; DMR-1700081; C-1839; 11674030; 310421113; 2016YFA0302300; SC0012432

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review B

Additional Journal Information:

Journal Volume: 102; Journal Issue: 21; 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; magnetic coupling; magnetic interactions; neutron scattering