Journal Article

FZJ-2021-00888

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Destruction of long-range magnetic order in an external magnetic field and the associated spin dynamics in Cu 2 GaBO 5 and Cu 2 AlBO 5 ludwigites

Kulbakov, A. A. ; Sarkar, R. ; Janson, O. ; Dengre, S. ; Weinhold, T. ; Moshkina, E. M. ; Portnichenko, P. Y. ; Luetkens, H. ; Yokaichiya, F. ; Sukhanov, A. S. ; Eremina, R. M. ; Schlender, P. ; Schneidewind, A.FZJ* ; Klauss, H.-H. ; Inosov, D. S. (Corresponding author)

2021
Inst. Woodbury, NY

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Please use a persistent id in citations: http://hdl.handle.net/2128/28677  doi:10.1103/PhysRevB.103.024447

Abstract: The quantum spin systems Cu2MBO5 (M = Al, Ga) with the ludwigite crystal structure consist of astructurally ordered Cu2+ sublattice in the form of three-leg ladders, interpenetrated by a structurally disorderedsublattice with a statistically random site occupation by magnetic Cu2+ and nonmagnetic Ga3+ or Al3+ ions. Amicroscopic analysis based on density-functional-theory calculations for Cu2GaBO5 reveals a frustrated quasitwo-dimensional spin model featuring five inequivalent antiferromagnetic exchanges. A broad low-temperature11B nuclear magnetic resonance points to a considerable spin disorder in the system. In zero magnetic field,antiferromagnetic order sets in below TN ≈ 4.1 K and ∼2.4 K for the Ga and Al compounds, respectively. Fromneutron diffraction, we find that the magnetic propagation vector in Cu2GaBO5 is commensurate and lies on theBrillouin-zone boundary in the (H0L) plane, qm = (0.45, 0, −0.7), corresponding to a complex noncollinearlong-range ordered structure with a large magnetic unit cell. Muon spin relaxation is monotonic, consisting of afast static component typical for complex noncollinear spin systems and a slow dynamic component originatingfrom the relaxation on low-energy spin fluctuations. Gapless spin dynamics in the form of a diffuse quasielasticpeak is also evidenced by inelastic neutron scattering. Most remarkably, application of a magnetic field above1 T destroys the static long-range order, which is manifested in the gradual broadening of the magnetic Braggpeaks. We argue that such a crossover from a magnetically long-range ordered state to a spin-glass regime mayresult from orphan spins on the structurally disordered magnetic sublattice, which are polarized in magnetic fieldand thus act as a tuning knob for field-controlled magnetic disorder.

Keyword(s): Magnetic Materials (1st) ; Condensed Matter Physics (2nd) ; Magnetism (2nd)

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Contributing Institute(s):

1. JCNS-FRM-II (JCNS-FRM-II)
2. Heinz Maier-Leibnitz Zentrum (MLZ)
3. Streumethoden (JCNS-2)
4. JCNS-4 (JCNS-4)

Research Program(s):

1. 632 - Materials – Quantum, Complex and Functional Materials (POF4-632) (POF4-632)
2. 6G4 - Jülich Centre for Neutron Research (JCNS) (FZJ) (POF4-6G4) (POF4-6G4)

Experiment(s):

1. PANDA: Cold three axes spectrometer (SR2)

Appears in the scientific report 2021

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