Spontaneous electric polarization in the B -site magnetic spinel GeCu 2 O 4

Yanda, Premakumar; Ghara, Somnath; Sundaresan, A.

doi:10.1016/j.ssc.2018.01.017

Cited by 6 publications

(4 citation statements)

References 29 publications

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“…Nevertheless, it is conceivable that weak structural changes in the magnetically ordered state reduce the symmetry, thus leading to a non-zero polarization. The step-like changes in the magnetic susceptibility and permittivity at T N [28], as well as the abrupt onset of the polarization in the magnetically ordered state [28,29], may indicate a weak first-order nature of the magnetic transition, similar to α-CaCr 2 O 4 , where the electric polarization has also been observed [71] at odds with the symmetry of the magnetic structure [72]. On the experimental side, further thermodynamic measurements probing the nature of the magnetic transition in Cu 2 GeO 4 , as well as dielectric measurements probing the direction of the electric polarization, can be useful.…”

Section: Discussion and Summarymentioning

confidence: 98%

“…Biquadratic exchange was considered as the driving force of this unusual order [22] and may explain it indeed [25], but appears irrelevant to Cu 2 GeO 4 , because biquadratic terms do not exist for spin-1 2 (they can be re-written as standard bilinear terms in the Hamiltonian [26,27], see Appendix A). Additionally, dielectric measurements revealed a clear anomaly in the permittivity at T N , as well as a non-zero electric polarization that appears below T N in this formally centrosymmetric (I4 1 /amd) crystal structure [28,29]. In the absence of spiral order that is typically associated with the electric polarization in chain cuprates [30][31][32][33], the origin of ferroelectricity in Cu 2 GeO 4 remains controversial [28].…”

Section: Structure and Properties Of Cu2geo4mentioning

confidence: 96%

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Origin of up-up-down-down magnetic order in Cu2GeO4

2019

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We use density-functional band-structure calculations to explore the origin of the up-up-downdown (UUDD) magnetic order in Cu2GeO4 with the frustrated J1 − J2 spin chains coupled into layers within the spinel-like crystal structure. In contrast to earlier studies, we find that the nearestneighbor coupling J1 may be negligibly small, owing to a nearly perfect compensation of the ferromagnetic direct exchange and antiferromagnetic superexchange. Under this condition, weak symmetric anisotropy of the exchange couplings gives rise to the UUDD order observed experimentally and also elucidates the non-trivial ordering pattern between the layers, whereas a small Dzyaloshinsky-Moriya interaction causes a spin canting that may generate local electric polarization. We argue that the buckling of the copper chains plays a crucial role in the suppression of J1 in Cu2GeO4 and sets this compound apart from other J1 − J2 chain magnets. I. INTRODUCTIONCopper oxides built by chains of edge-sharing CuO 4 plaquettes serve as material prototypes of frustrated spin-1 2 chains with competing nearest-neighbor and nextnearest-neighbor interactions J 1 and J 2 , respectively. This simple spin model received ample attention [1] triggered by the prospects of chiral, multipolar, and spinnematic phases that may occur therein [2][3][4][5][6][7][8]. Whereas long-range order does not take place in one dimension (1D), interchain couplings in real materials will usually cause three-dimensional (3D) collinear or noncollinear order depending on the J 2 /J 1 ratio. On the classical level, incommensurate spiral order appears for J 2 /|J 1 | > 1 4 , whereas at J 2 /|J 1 | < 1 4 the second-neighbor coupling is not strong enough to tilt the spins, and the collinear ferromagnetic or up-down-up-down antiferromagnetic order form depending on the sign of J 1 . Quantum effects preserve the spiral state in the case of ferromagnetic (FM) J 1 [9], but destroy the order and open a spin gap for antiferromagnetic (AFM) J 1 at J 2 /J 1 > 0.241 [10][11][12].Real-world prototypes of the J 1 − J 2 spin chains will typically follow one of these scenarios. The majority of quasi-1D copper oxides reveal J 2 /|J 1 | > 1 4 with FM J 1 and develop the incommensurate spiral order [13][14][15][16]. Li 2 CuO 2 [17,18] and CuAs 2 O 4 [19] are notable exceptions, where J 1 is also FM, but J 2 /|J 1 | < 1 4 renders spin alignment along the chains purely ferromagnetic. Spin-chain compounds with AFM J 1 are more rare, although tentative indications of the spin-gap formation at J 2 /J 1 > 0.241 have been reported [20].One puzzling case in this series is Cu 2 GeO 4 [21] that reveals an unanticipated antiferromagnetic up-up-downdown (UUDD) order [22] despite the prediction of FM J 1 * altsirlin@gmail.com and AFM J 2 , both of the same magnitude [23]. This parameter regime would normally lead to the incommensurate spiral order, similar to LiCuVO 4 , CuCl 2 , and other J 1 − J 2 cuprates. Here, we address this discrepancy and first analyze whether additional terms beyond J 1 and J 2 could...

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Section: Discussion and Summarymentioning

confidence: 98%

Section: Structure and Properties Of Cu2geo4mentioning

confidence: 96%

Origin of up-up-down-down magnetic order in Cu2GeO4

2019

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“…This unusual ordering pattern was attributed to the presence of a biquadratic exchange interaction active in this compound [14] while an a posteriori DFT study argued that the actual reason is the negligibly small nearest-neighbor coupling [29]. Surprisingly, two independent groups recently reported spin-induced multiferroicity in GCO emerging at T N ∼ 33 K [15,16], which is incompatible with any theoretically proposed or experimentally determined magnetic structures [14,27,28]. To date, the nature of multiferroicity in GCO remains largely unknown.…”

mentioning

confidence: 84%

“…In this paper, we report on epitaxially stabilized thin films of two members of the "4-2" spinel family, GeNi 2 O 4 (GNO) * vasyukov@physics.msu.ru and GeCu 2 O 4 (GCO), which exhibit very different lowdimensional magnetic behavior. The bulk GNO undergoes a peculiar two-stage phase transition into a two-dimensional (2D) magnetic ground state [7][8][9][10][11][12], while the bulk GCO shows a multiferroic transition with interacting 1D S = 1/2 chains [13][14][15][16].…”

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confidence: 99%

Epitaxial stabilization of thin films of the frustrated Ge-based spinels

Vasiukov

Kareev

Wen

et al. 2021

Phys. Rev. Materials

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Frustrated magnets can host numerous exotic many-body quantum and topological phenomena. GeNi 2 O 4 is a three-dimensional S = 1 frustrated magnet with an unusual two-stage transition to the two-dimensional antiferromagnetic ground state, while GeCu 2 O 4 is a high-pressure phase with a strongly tetragonally elongated spinel structure and magnetic lattice formed by S = 1/2CuO 2 linear chains with frustrated interchain exchange interactions and exotic magnetic behavior. Here, we report on the thin-film epitaxial stabilization of these two compounds. The developed growth mode, surface morphology, crystal structure, and copper valence state were characterized by in situ reflection high-energy electron diffraction, atomic force microscopy, x-ray reflectivity, x-ray diffraction, x-ray photoelectron spectroscopy, and resonant x-ray absorption spectroscopy. Our results pave an alternative route to the comprehensive investigation of the puzzling magnetic properties of these compounds and the exploration of emergent features driven by strain.

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Multiferroicity in a quasi-one-dimensional magnet MnSb2Se4

Kumar

Sundaresan

2022

Materials Research Bulletin

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Spontaneous electric polarization in the B -site magnetic spinel GeCu 2 O 4

Cited by 6 publications

References 29 publications

Origin of up-up-down-down magnetic order in Cu2GeO4

Origin of up-up-down-down magnetic order in Cu2GeO4

Epitaxial stabilization of thin films of the frustrated Ge-based spinels

Multiferroicity in a quasi-one-dimensional magnet MnSb2Se4

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