Softening of breathing elastic mode and trigonal elastic mode in the disordered pyrochlore magnet NaCaCo2F7

Watanabe, T.; Kato, H.; Hara, Y.; Krizan, J. W.; Cava, R. J.

doi:10.1103/physrevb.101.214425

Title: Softening of breathing elastic mode and trigonal elastic mode in the disordered pyrochlore magnet NaCaCo₂F₇

Abstract

Cobalt pyrochlore fluoride NaCaCo₂F₇ is a disordered frustrated magnet that is composed of Co²⁺ ions with an effective spin-12 magnetic moment and that exhibits spin freezing below $$T_f ~$$ 2.4 K. Here, we perform ultrasound velocity measurements on a single crystal of the cubic NaCaCo₂F₇. The temperature dependence of the bulk modulus (the breathing elastic mode) exhibits Curie-type softening upon cooling below ~20 K down to $$T_f$$, which is suppressed by the magnetic field. This Curie-type softening should be a precursor to the enhancement of the strength of exchange disorder via the spin-lattice coupling, which causes the spin freezing. In contrast to the magnetic-field-suppressed Curie-type softening in the bulk modulus, the trigonal shear modulus exhibits softening with a characteristic minimum upon cooling, which is enhanced by the magnetic field at temperatures below ~20 K. This magnetic-field-enhanced elastic anomaly in the trigonal shear modulus suggests a coupling of the lattice to the dynamical spin-cluster state. For NaCaCo₂F₇, the observed elastic anomalies reveal an occurrence of magnetic-field-induced crossover from an isostructural lattice instability toward the spin freezing to a trigonal lattice instability arising from the emergent dynamical spin-cluster state.

Authors:

Watanabe, T. ^[1]; Kato, H. ^[1]; Hara, Y. ^[2]; Krizan, J. W. ^[3]; Cava, R. J. ^[3]

Nihon Univ., Tokyo (Japan)
Ibaraki College, Hitachinaka (Japan)
Princeton Univ., NJ (United States)

Publication Date:: Mon Jun 15 00:00:00 EDT 2020

Research Org.:: Johns Hopkins Univ., Baltimore, MD (United States); Energy Frontier Research Centers (EFRC) (United States). Institute for Quantum Matter

Sponsoring Org.:: USDOE Office of Science (SC), Basic Energy Sciences (BES); Ministry of Education, Culture, Sports, Science and Technology (MEXT)

OSTI Identifier:: 1803705

Grant/Contract Number:: SC0019331; 17K05520

Resource Type:: Accepted Manuscript

Journal Name:: Physical Review B

Additional Journal Information:: Journal Volume: 101; 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; Materials Science; Physics

Citation Formats


                    Watanabe, T., Kato, H., Hara, Y., Krizan, J. W., and Cava, R. J. Softening of breathing elastic mode and trigonal elastic mode in the disordered pyrochlore magnet NaCaCo2F7.  United States: N. p., 2020. 
Web.  doi:10.1103/physrevb.101.214425.

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                    Watanabe, T., Kato, H., Hara, Y., Krizan, J. W., & Cava, R. J. Softening of breathing elastic mode and trigonal elastic mode in the disordered pyrochlore magnet NaCaCo2F7.  United States.  https://doi.org/10.1103/physrevb.101.214425

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                    Watanabe, T., Kato, H., Hara, Y., Krizan, J. W., and Cava, R. J. Mon .  
"Softening of breathing elastic mode and trigonal elastic mode in the disordered pyrochlore magnet NaCaCo2F7".  United States.  https://doi.org/10.1103/physrevb.101.214425.  https://www.osti.gov/servlets/purl/1803705.

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@article{osti_1803705,

  title        = {Softening of breathing elastic mode and trigonal elastic mode in the disordered pyrochlore magnet NaCaCo2F7},

  author       = {Watanabe, T. and Kato, H. and Hara, Y. and Krizan, J. W. and Cava, R. J.},

  abstractNote = {Cobalt pyrochlore fluoride NaCaCo2F7 is a disordered frustrated magnet that is composed of Co2+ ions with an effective spin-12 magnetic moment and that exhibits spin freezing below $T_f ~$ 2.4 K. Here, we perform ultrasound velocity measurements on a single crystal of the cubic NaCaCo2F7. The temperature dependence of the bulk modulus (the breathing elastic mode) exhibits Curie-type softening upon cooling below ~20 K down to $T_f$, which is suppressed by the magnetic field. This Curie-type softening should be a precursor to the enhancement of the strength of exchange disorder via the spin-lattice coupling, which causes the spin freezing. In contrast to the magnetic-field-suppressed Curie-type softening in the bulk modulus, the trigonal shear modulus exhibits softening with a characteristic minimum upon cooling, which is enhanced by the magnetic field at temperatures below ~20 K. This magnetic-field-enhanced elastic anomaly in the trigonal shear modulus suggests a coupling of the lattice to the dynamical spin-cluster state. For NaCaCo2F7, the observed elastic anomalies reveal an occurrence of magnetic-field-induced crossover from an isostructural lattice instability toward the spin freezing to a trigonal lattice instability arising from the emergent dynamical spin-cluster state.},

  doi          = {10.1103/physrevb.101.214425},

  journal      = {Physical Review B},

  number       = 21,

  volume       = 101,

  place        = {United States},

  year         = {Mon Jun 15 00:00:00 EDT 2020},

  month        = {Mon Jun 15 00:00:00 EDT 2020}

}

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Title: Softening of breathing elastic mode and trigonal elastic mode in the disordered pyrochlore magnet NaCaCo2F7

Abstract

Citation Formats

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Molecular Spin Resonance in the Geometrically Frustrated Magnet MgCr 2 O 4 by Inelastic Neutron Scattering journal, October 2008

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Spin freezing in the disordered pyrochlore magnet NaCaCo 2 F 7 : NMR studies and Monte Carlo simulations journal, December 2017

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Temperature Dependence of the Elastic Constants journal, November 1970

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Title: Softening of breathing elastic mode and trigonal elastic mode in the disordered pyrochlore magnet NaCaCo₂F₇

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Spin-Orbit Fluctuations in Frustrated Heavy-Fermion Metal ${LiV}_{2} O_{4}$
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Molecular Spin Resonance in the Geometrically Frustrated Magnet ${MgCr}_{2} O_{4}$ by Inelastic Neutron Scattering
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Liquidlike correlations in single-crystalline Y $_{2}$ Mo $_{2}$ O $_{7}$ : An unconventional spin glass
journal, February 2014

A Theory of the Cooperative Jahn-Teller Effect –Crystal Distortions in Cu _{1- x} Ni _x Cr ₂ O ₄ and Fe _{1- x} Ni _x Cr ₂ O ₄ –
journal, January 1972

Acoustic study of dynamical molecular-spin state without magnetic phase transition in spin-frustrated ${ZnFe}_{2} O_{4}$
journal, November 2015

Orbital-spin-coupled fluctuations in spinel vanadate MnV $_{2}$ O $_{4}$
journal, February 2013

Freezing of spin correlated nanoclusters in a geometrically frustrated magnet
journal, June 2002

Frustrated Magnetism and Cooperative Phase Transitions in Spinels
journal, January 2010

Emergence of Highly Degenerate Excited States in the Frustrated Magnet ${MgCr}_{2} O_{4}$
journal, February 2013

Quadrupolar effect in the perovskite manganite ${La}_{1 - x} {Sr}_{x} {MnO}_{3}$
journal, December 2000

A Spin Molecule Model for Geometrically Frustrated Spinel ZnFe ₂ O ₄
journal, January 2011

Observation of elastic anomalies driven by coexisting dynamical spin Jahn-Teller effect and dynamical molecular-spin state in the paramagnetic phase of frustrated MgCr $_{2}$ O $_{4}$
journal, October 2012

Elastic properties and cooperative Jahn-Teller effect in nickel chromite
journal, February 1973

Orbital- and spin-driven lattice instabilities in quasi-one-dimensional ${CaV}_{2} O_{4}$
journal, September 2018

Static and dynamic $X Y$ -like short-range order in a frustrated magnet with exchange disorder
journal, January 2016

Single-ion properties of the $S_{eff}$ = $\frac{1}{2}$ XY antiferromagnetic pyrochlores $Na A^{'} {Co}_{2} F_{7}$ ( $A^{'} = {Ca}^{2 +}, {Sr}^{2 +}$ )
journal, April 2017

${NaCaCo}_{2} F_{7}$ : A single-crystal high-temperature pyrochlore antiferromagnet
journal, June 2014

Avoided valence transition in a plutonium superconductor
journal, March 2015

Spin-glass transition in geometrically frustrated antiferromagnets with weak disorder
journal, January 2010

Real-space investigation of short-range magnetic correlations in fluoride pyrochlores ${NaCaCo}_{2} F_{7}$ and ${NaSrCo}_{2} F_{7}$ with magnetic pair distribution function analysis
journal, December 2017

Jahn-Teller inactivity and magnetic frustration in ${GeCo}_{2} O_{4}$ probed by ultrasound velocity measurements
journal, September 2008

NaSrCo ₂ F ₇ , a Co ²⁺ pyrochlore antiferromagnet
journal, July 2015

Molecular spin-orbit excitations in the $J_{eff}$ = $\frac{1}{2}$ frustrated spinel GeCo $_{2}$ O $_{4}$
journal, August 2011

NaSrMn ₂ F ₇ , NaCaFe ₂ F ₇ , and NaSrFe ₂ F ₇ : novel single crystal pyrochlore antiferromagnets
journal, November 2016

Strongly Geometrically Frustrated Magnets
journal, August 1994

Magnetic interactions and spin dynamics in the bond-disordered pyrochlore fluoride ${NaCaCo}_{2} F_{7}$
journal, April 2019

Physical Acoustics in the Solid State
book, January 2005