NaCuMoO₄(OH) as a Candidate Frustrated J₁–J₂ Chain Quantum Magnet

Abstract

In a frustrated J1-J2 chain with the nearest-neighbor ferromagnetic interaction J1 and the nextnearest-neighbor antiferromagnetic interaction J2, novel magnetic states such as a spin-nematic state are theoretically expected. However, they have been rarely examined in experiments because of the difficulty in obtaining suitable model compounds. We show here that the quasi-one-dimensional antiferromagnet NaCuMoO4(OH), which comprises edge-sharing CuO2 chains, is a good candidate J1-J2 chain antiferromagnet. The exchange interactions are estimated as J1 = −51 K and J2 = 36 K by comparing the magnetic susceptibility, heat capacity, and magnetization data with the data obtained using calculations by the exact diagonalization method. High-field magnetization measurements at 1.3 K show a saturation above 26 T with little evidence of a spin nematic state expected just below the saturation field, which is probably due to smearing effects caused by thermal fluctuations and the polycrystalline nature of the sample.Low-dimensional quantum spin systems with geometrical frustration and/or competing magnetic interactions have attracted much attention in the field of magnetism. Low dimensionality, quantum fluctuations, and frustration are three ingredients that may effectively suppress conventional magnetic order and lead us to unconventional magnetic order or exotic ground states such as a quantum spin liquid [1,2].A frustrated J 1 -J 2 chain of spin 1/2 defined asprovides us with an interesting example: the competition between the nearest-neighbor (NN) ferromagnetic interaction J 1 and the next-nearest-neighbor (NNN) antiferromagnetic interaction J 2 causes various quantum states in magnetic fields h [3][4][5][6][7]. Realized in low fields is a long-range order of vector chirality defined as (s l × s l+n ) z (n = 1, 2). As the field increases, spin correlations change markedly because bound magnon pairs are stabilized by ferromagnetic J 1 . The bound magnon pairs form a spin density wave (SDW) in medium fields, whereas, in high fields just below the saturation of magnetization, they exhibit Bose-Einstein condensation into quantum multipolar states [8][9][10][11]. One of the multipolar states expected just below the saturation is a quadrupolar state of magnon pairs called a spin nematic state, analogous to nematic liquid crystals. To explore these quantum states theoretically predicted for the frustrated J 1 -J 2 chain, many experimental studies have been performed on quasi-1D compounds * knawa@issp.u-tokyo.ac.jp † Present address: Department of Applied Physics, Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan TABLE I. Candidate compounds for the J1-J2 chain system. Listed are the nearest-neighbor intrachain interaction J1, the next-nearest-neighbor interaction J2, the bond angles of Cu-O-Cu paths for J1, the antiferromagnetic transition temperature at zero field TN, and the saturation field Hs. Thus, according to the Goodenough-Kanamori rule, J 1 should be ferromagnetic while J 2 can be antife...

Orbital Arrangements and Magnetic Interactions in the Quasi-One-Dimensional Cuprates ACuMoO4(OH) (A = Na, K)

“…In fact, the CW temperature is estimated to be -205 K for the χ in the range of 250-300 K at H // a. Note that this CW temperature can be an underestimate (17) b (Å) 6.31560 (14) c (Å) 9.5641(4)…”

“…The red, green, and blue curves are obtained at H // a, b, and c, respectively, for KCuMoO4(OH). The black curve represents the χ of NaCuMoO4(OH) for comparison 14 ; χ of the polycrystalline sample is shown since its anisotropy is small. The inset shows a blowup around the broad maximum.…”

“…In addition, there is a super-superexchange interaction J2 through Cu-O-O-Cu paths along the chain, which is antiferromagnetic. In fact, the exchange interactions of NaCuMoO4(OH) are estimated as J1 = -51 K and J2 = 36 K. 14 Note that the two interactions cause frustration in the spin chain, because J1 favors all the spins in the same direction whereas J2 tends to make every second spins antiparallel. This frustration can lead to a variety of magnetic phases such as spin nematic order, which is theoretically predicted to be a sort of spin liquid with an unusual spin order analogous to the nematic state in liquid crystals [16][17][18][19] but has not yet been observed in actual compounds 20 .…”

Dynamics of linarite: Observations of magnetic excitations

“…One of them expected just below saturation is the quadrupolar state of bound magnon pairs which is termed the spin-nematic state 19 . The J 1 -J 2 model has been used to describe various quasi-1D edge-sharing cuprates 12,[21][22][23][24][25][26][27][28][29] . Unfortunately, for many of the candidates for exhibiting multipolar phases, the involved AFM magnetic couplings and thus the saturation field are quite large, making it difficult to probe the multipolar phases.…”

“…Especially, the so-called spin-nematic state has recently received strong interest [9][10][11][12][13][14] . The spin-nematic phase can be likened to the arrangement of molecules in nematic liquid crystals.…”