Impact of Mn–O–O–Mn superexchange pathways in a honeycomb lattice Mn oxide with small charge-transfer energy

Abstract

We investigated the electronic structure of layered Mn oxide Bi3Mn4O12(NO3) with a Mn honeycomb lattice by x-ray absorption spectroscopy. The valence of Mn was determined to be 4+ with a small charge-transfer energy. We estimated the values of superexchange interactions up to the fourth nearest neighbors (J1, J2, J3, and J4) by unrestricted Hartree-Fock calculations and a perturbation method. We found that the absolute values of J1 through J4 are similar with positive (antiferromagnetic) J1 and J4, and negative (ferromagnetic) J2 and J3, due to Mn-O-O-Mn pathways activated by the smallness of charge-transfer energy. The negative J3 provides magnetic frustration in the honeycomb lattice to prevent long-range ordering.PACS numbers: 71.30.+h, 71.28.+d, 79.60.Dp, Since the resonating valence bond state in geometrically frustrated magnets has been proposed by Anderson [1], spin-disordered ground states in Mott insulators on frustrated lattices have been attracting great interest in condensed-matter physics. The exchange interaction J in a Mott insulator is roughly given by −2t 2 /E g , where t is the transfer integral between the two localized orbitals and E g is the excitation energy across the Mott gap. In Mott insulators on frustrated lattices, spin-disordered systems including organic and inorganic materials [2][3][4][5][6] all have relatively small E g , suggesting that the smallness of E g or the closeness to the Mott transition would be important to realize the spin-disordered ground states.Various insulating transition-metal oxides are known as Mott insulators and can be classified into (i) the Mott-Hubbard type insulators where the Mott gap E g is mainly determined by the Coulomb interaction U between the transition-metal d electrons and (ii) the chargetransfer type insulators where E g is determined by the charge-transfer energy ∆ from the oxygen p state to the transition-metal d state [7]. Therefore, the smallness of E g can be obtained in transition-metal oxides with small U or small ∆. In the small U case, theoretical studies on triangular-lattice Hubbard models proved that a spin-disordered phase is realized near the Mott transition [8][9][10][11], which could be related to the higher order exchange terms. As for the small ∆ case, in addition to

Frustrated magnetic interactions in an S=3/2 bilayer honeycomb lattice compound Bi3Mn4O12<

“…The low critical magnetic field suggests that the disordered ground state and the magnetic-field induced state are energetically close. The intrabilayer couplings were suggested to be important to explain the disordered ground state [20,21]. It was reported that an large intrabilayer antiferromagnetic nearest-neighbor coupling gives rise to dimerization [22][23][24][25].…”

“…It was reported that an large intrabilayer antiferromagnetic nearest-neighbor coupling gives rise to dimerization [22][23][24][25]. On the other hand, the frustrating further-neighbor interactions beyond those of second-neighbors both inplane and intrabilayer were suggested to cause the disordered state [18,21,[26][27][28][29]. Although these further-neighbor interactions should be important, the bilayer structure with many relevant interac- tions makes the detailed analysis of the inelastic neutron scattering results challenging.…”

AAg2(M′1/3M2/3)[VO4]2: Synthesis, Magnetic Properties, and Lattice Dynamics of Honeycomb-Type Lattices

“…An important and interesting aspect of low-dimensional compounds relates to superexchange pathways between magnetic ions via nonmagnetic ligands (e.g., O 2– ) or complex units like [VO 4 ] 3– . This can be described by a super exchange (SE), − i.e., M O M, or by a supersuper exchange (SSE), − i.e., M O–V–O M . Two-dimensional layered compounds of the type, AAg 2 M­[VO 4 ] 2 − and ANa 2 M­[VO 4 ] 2 contain magnetic metal ions (M) on a triangular lattice, where magnetic ions are linked via the nonmagnetic [VO 4 ] 3– unit.…”

“…The BaAg 2 Mn­[VO 4 ] 2 compound is an example for the realization of frustrated triangular lattice antiferromagnet . The Cu 2+ compound is interesting because both ferromagnetic and antiferromagnetic interactions in one dimension (chain) are present and result in an intriguing behavior of their thermodynamic properties. , For further work on nontrivial ground states in low-dimensional spin-systems, see for example refs − .…”

Calculation of magnetic exchange couplings in theS=3/2honeycomb system (Bi3MnKandpal1, Brink2 2011Phys. Rev. B

“…The lack of spontaneous magnetic ordering within the Mn honeycomb lattices down to very low temperature was proposed to be due to frustration of magnetic interactions, in particular a competition between first and second neighbor antiferromagnetic Mn-Mn exchange interactions 2 . Currently BMNO is therefore viewed as a model system with strongly fluctuating S=3/2 spins on honeycomb lattice, with a magnetic frustration that is due to the presence of longer-range antiferromagnetic exchange interactions [2][3][4][5][6][7][8] .…”