Non-Kramers Freezing and Unfreezing of Tunneling in the Biaxial Spin Model

Abstract

The ground state tunnel splitting for the biaxial spin model in the magnetic field, H = -D S_{x}^2 + E S_{z}^2 - g μ_B S_z H_z, has been investigated using an instanton approach. We find a new type of spin instanton and a new quantum interference phenomenon associated with it: at a certain field, H_2 = 2SE^{1/2}(D+E)^{1/2}/(g μ_B), the dependence of the tunneling splitting on the field switches from oscillations to a monotonic growth. The predictions of the theory can be tested in Fe_8 molecular nanomagnets.

7 pages, minor changes, published in EPL

References in corpus (4)

• Quantum-Classical Transition of the Escape Rate of a Uniaxial Spin System in an Arbitrarily Directed Field
• Quantum Coherence in Fe8 Molecular Nanomagnets
• Complex Instantons and Charged Rotating Black Hole Pair Creation
• Macroscopic quantum coherence in mesoscopic ferromagnetic systems

Cited by in corpus (9)

• Quantum phase interference and spin parity in Mn12 single-molecule magnets
• Quantum phase interference (Berry phase) in single-molecule magnets of Mn12
• Macroscopic quantum tunneling and quantum-classical phase transitions of the escape rate in large spin systems
• Geometric-phase interference in a Mn_{12} single-molecule magnet with four-fold rotational symmetry
• Geometric-Phase-Effect Tunnel-Splitting Oscillations in Single-Molecule Magnets with Fourth-Order Anisotropy Induced by Orthorhombic Distortion
• Intermediate spin, Schrödinger cat states and nano-magnets
• Resonant tunnelling and quenching of tunnel splitting in Wess-Zumino nanospin systems
• Quadrupole Excitation in Tunnel Splitting Oscillation in Nano-Particle $M{n}_{12}$
• Non-Kramers degeneracy and oscillatory tunnel splittings in the biaxial Spin System