Exchange Interactions Mediated by Nonmagnetic Cations in Double Perovskites

Abstract

Establishing the physical mechanism governing exchange interactions is fundamental for exploring exotic phases such as quantum spin liquids (QSLs) in real materials. In this work, we address exchange interactions in Sr2CuTexW1−xO6, a series of double perovskites that realize a spin-1/2 square lattice and are suggested to harbor a QSL ground state arising from the random distribution of non-magnetic ions. Our ab initio multi-reference configuration interaction calculations show that replacing Te atoms with W atoms changes the dominant couplings from nearest to nextnearest neighbor due to the crucial role of unoccupied states of the non-magnetic ions in the supersuperexchange mechanism. Combined with spin-wave theory simulations, our calculated exchange couplings provide an excellent description of the inelastic neutron scattering spectra of the parent compounds, as well as explaining that the magnetic excitations in Sr2CuTe0.5W0.5O6 emerge from bond-disordered exchange couplings. Our results demonstrate the crucial role of the non-magnetic cations in exchange interactions paving the way to further explore QSL phases in bond-disordered materials.In 3d transition metal (TM) oxides, the on-site Coulomb repulsive interactions between the electrons are strong enough to confine them to the TM sites, leading to the formation of localized spin or spin-orbital moments [1]. The manner in which these moments couple to each other is primarily governed by the underlying exchange interactions, which may be direct and/or mediated by the intermediate anions or ligands (L), the latter is also referred to as the superexchange. There are many possible ways these interactions can manifest, resulting in a plethora of magnetically ordered states such as ferromagnetic and different types of antiferromagnetic (AFM) order, magnetic spirals or more exotic topologically protected magnetic textures such as Skyrmions [1][2][3][4].Even more fascinating ground states that stem from exchange interactions are those which do not undergo any magnetic ordering even at absolute zero temperature, e.g. spin-liquid states in low-dimensional magnetic systems [5]. Broken-symmetry valence-bond solids and QSLs where symmetry is conserved are examples of such phases [5][6][7]. In these quantum paramagnetic phases, the long-range magnetic order is typically destroyed by frustrated exchange interactions and quantum fluctuations [8]. In the simplistic and prototypical two-dimensional spin-1/2 Heisenberg square lattice (HSL) model, the ratio of nearest-neighbor (NN) J 1 and AF next-nearest neighbor (NNN) J 2 exchange interac-tions of ∼0.5 results in magnetic frustration and a QSL ground state [7].The exchange mechanisms in TM compounds, principally the superexchange, are reasonably well understood in the form of the Goodenough-Kanamori-Anderson (GKA) rules [1]. The highly successful GKA rules correctly predict the sign of magnetic coupling for the 180 • and 90 • TM-L-TM bond angles. In double perovskite compounds like Sr 2 CuTeO 6 and Sr 2 CuWO 6 the magnetic Cu...

Site-Selective d10/d0 Substitution in an S = 1/2 Spin Ladder Ba2CuTe1–xWxO6 (0 ≤ x ≤ 0.3)

“…We have recently shown that diamagnetic d 10 and d 0 cations on the linking -B''-site have a significant effect on the magnetic interactions and ground states in double perovskites. 6,9 We investigated this d 10 /d 0 effect in the cubic double perovskites Ba2MnTeO6 and Ba2MnWO6, in which the magnetic Mn 2+ cations are linked by either 4d 10 Te 6+ or 5d 0 W 6+ cations. In these isostructural materials, Mn 2+ S = 5/2 magnetism is described using a simple fcc Heisenberg model consisting of a 90° (nearest neighbor (NN) -J1) and 180° (next-nearest neighbor (NNN) -J2) Mn-O-(Te/W)-O-Mn interaction (Figure 1a).…”

Scrutinizing the stability and exploring the dependence of thermoelectric properties on band structure of 3d-3d metal-based double perovskites Ba2FeNiO6 and Ba2CoNiO6

“…The B–O–B′ bond angle in A 2 BB′O 6 features the type of exchange interaction 33 . The B–B′ interactions of double perovskites can be gradually altered by carefully manipulating the B–O–B′ bond angle to obtain the desired properties 34 , 35 . If both B and B′ are magnetic, the magneto-electronic structure of such configuration is governed by B–B′ interaction.…”

Topological magnon insulators in two-dimensional van der Waals ferromagnets CrSiTe$_3$ and CrGeTe$_3$: towards intrinsic gap-tunability

“…One possible explanation would be that the sp3 hybridized orbitals of Si/Ge atoms in the honeycomb center are strongly coupled with the p orbitals of Te atoms and subsequently strongly influence the strength of the Cr-Te-Cr superexchange interaction. Similar orbital hybridization effect is not rare since the super-exchange interaction mediated by nonmagnetic ions is also proposed in inverse-trirutile compound [44] and double-perovskites [45]. In any case, if CrXTe 3 is dominated by the Kitaev interaction, then a strong in-plane anisotropy should be easily evident in the magnetization measurements, which has never been reported.…”