Thermodynamics of a frustrated quantum magnet on a square lattice

Abstract

We report the magnetic and calorimetric measurements in single crystal samples of the square lattice J1 − J2 quantum antiferromagnet BaCdVO(PO4)2. An investigation of the scaling of magnetization reveals a "dimensionality reduction" indicative of a strong degree of geometric frustration. Below a characteristic temperature of T * 150 mK we observe the emergence of an additional strongly fluctuating quantum phase close to full magnetic saturation. It is separated from the magnetically ordered state by first-and second-order phase transitions, depending on the orientation of the applied magnetic field. We suggest that this phase may indeed be related to the theoretically predicted spin-nematic state. * povarovk@phys.ethz.ch † http://www.neutron.ethz.ch/ material features strong geometric frustration (J 2 /J 1 −0.9) and easily accessible energy scales (saturation field about 4 T, AF order below T N = 1.05 K). The hightemperature thermodynamics is consistently described by J 1 = −3.6 K and J 2 = 3.2 K [12]. For lack of other candidates, BaCdVO(PO 4 ) 2 has been a subject of intense arXiv:1807.09549v2 [cond-mat.str-el]

Putative spin-nematic phase in BaCdVO(PO4)2

“…Translating this propagation vector into the theoretical language of the square lattice of V ions, one finds q sq = (0, 1/4), where q sq is defined relative to an idealized 1-site unit cell. Thus our samples do not realize the columnar q sq = (0, 1/2) magnetic order that was previously proposed from fitting high-temperature series expansions of a J 1 -J 2 Heisenberg model to magnetic susceptibility measurements [31] and assumed thereafter [36].…”

“…These results were interpreted in terms of a model with 1 st -neighbor exchange J 1 ≈ −3.6 K and 2 nd -neighbor exchange J 2 ≈ 3.2 K [31], for which the low-field ordered state would be a canted AFM with propagation vector q sq = (1/2, 0) [33][34][35]. Subsequent thermodynamic measurements have extended the magnetic phase diagram of BaCdVO(PO 4 ) 2 , filling in the gaps at high field, and identifying a new low-temperature phase bordering the saturated state [36], precisely where one might expect a BSN to occur [2,10,[14][15][16][18][19][20][21]. This is an exciting development, since the range of fields involved, 4 < ∼ H < ∼ 5 T [36], is much lower than in other candidate systems [22][23][24][25], making it accessible to a wider range of experimental techniques.…”

“…Subsequent thermodynamic measurements have extended the magnetic phase diagram of BaCdVO(PO 4 ) 2 , filling in the gaps at high field, and identifying a new low-temperature phase bordering the saturated state [36], precisely where one might expect a BSN to occur [2,10,[14][15][16][18][19][20][21]. This is an exciting development, since the range of fields involved, 4 < ∼ H < ∼ 5 T [36], is much lower than in other candidate systems [22][23][24][25], making it accessible to a wider range of experimental techniques. Despite this progress, the nature of the low-field phase in BaCdVO(PO 4 ) 2 , the form of its magnetic interactions, and the possibility of a BSN in high field, all remain open questions.In this Letter we use a combination of neutron scattering and AC susceptibility measurements to determine the arXiv:1903.12462v1 [cond-mat.str-el]…”

Possible observation of quantum spin-nematic phase in a frustrated magnet

“…We note that while this article was under review, two studies have also reported the possibility of SN order in the square-lattice frustrated ferromagnet BaCdVO(PO 4 ) 2 (29, 30).…”

Realizing square and diamond lattice S=1/2 Heisenberg antiferromagnet models in the α and β phases of the coordination framework, Abdeldaim1, Li2, Farrar3 et al. 2020Phys. Rev. Materials

“…Indeed, in a recent theoretical and experimental investigation of the solid-solution, Sr 2 Cu(Te 1-x W x )O 6 where x = 0 and x = 1 represent Néel and columnar ordered systems, respectively, QSL signatures have been observed for the x = 0.5 compound [17]. Interestingly, the behavior exhibited by complex materials derived from the FSL, such as BaCdVO(PO 4 ) 2 [6], where signatures of a spinnematic ground state have been observed in an applied field [18,19], has further enriched the phase diagram of FSL materials, leading to new theoretical predictions [20]. By extending the J 1 −J 2 model to incorporate the effects of interplanar coupling, J 3 , magnetic ground states inaccessible to the pure FSL model can also be realized [21].…”