Spin–orbit coupled molecular quantum magnetism realized in inorganic solid

Abstract

Molecular quantum magnetism involving an isolated spin state is of particular interest due to the characteristic quantum phenomena underlying spin qubits or molecular spintronics for quantum information devices, as demonstrated in magnetic metal–organic molecular systems, the so-called molecular magnets. Here we report the molecular quantum magnetism realized in an inorganic solid Ba3Yb2Zn5O11 with spin–orbit coupled pseudospin-½ Yb3+ ions. The magnetization represents the magnetic quantum values of an isolated Yb4 tetrahedron with a total (pseudo)spin 0, 1 and 2. Inelastic neutron scattering results reveal that a large Dzyaloshinsky–Moriya interaction originating from strong spin–orbit coupling of Yb 4f is a key ingredient to explain magnetic excitations of the molecular magnet states. The Dzyaloshinsky–Moriya interaction allows a non-adiabatic quantum transition between avoided crossing energy levels, and also results in unexpected magnetic behaviours in conventional molecular magnets.

Behavior of the breathing pyrochlore lattice Ba3Yb2Zn5O11 in applied magnetic field

“…4. This data is consistent with previous studies of Ba 3 Yb 2 Zn 5 O 11 [5,7,8]. Further details are provided in Fig.…”

“…Our experimental INS results are generally consistent with those of Ref. [8], but we find that, to obtain good agreement with model calculations, careful consideration of the direction of the applied field in relation to the experimental geometry is essential. The resulting single tetrahedron model provides a good description of the INS data as well as the heat capacity at low fields.…”

“…As described in Ref. [8] and in Sec. III below, these changes are associated with level crossings of the single tetrahedron ground state with one of the excited states.…”

“…The lack of evidence of magnetic ordering in this compound, combined with a residual entropy of ∼ log 2 per small tetrahedron strongly suggests that the inter-tetrahedron coupling is weak [4], with the material being described by essentially decoupled tetrahedral units [5,7,8]. The physics of these decoupled tetrahedra has been firmly established by several inelastic neutron scattering (INS) studies [5,7,8]. These investigations, and the associated theoretical models, have revealed that the intra-tetrahedron physics originates from dominant antiferromagnetic Heisenberg exchange [4] coupled with an unusually strong Dzyaloshinskii-Moriya (DM) interactions [5,7,8].…”

“…Note that due to the correlation between the field and wavevector directions, this is not equivalent to averaging over botĥ Q andB separately, as was stated in Ref. [8].…”