title: Studies on a frustrated Heisenberg spin chain with alternating ferromagnetic and antiferromagnetic exchanges.
abstract: We study Heisenberg spin-1/2 and spin-1 chains with alternating ferromagnetic (J(F)(1)) and antiferromagnetic (J(A)(1)) nearest-neighbor interactions and a ferromagnetic next-nearest-neighbor interaction (J(F)(2)). In this model frustration is present due to the non-zero J(F)(2). The model with site spin s behaves like a Haldane spin chain, with site spin 2s in the limit of vanishing J(F)(2)and large J(F)(1)/J(A)(1). We show that the exact ground state of the model can be found along a line in the parameter space. For fixed J(F)(1), the phase diagram in the space of J(A)(1)-J(F)(2) is determined using numerical techniques complemented by analytical calculations. A number of quantities, including the structure factor, energy gap, entanglement entropy and zero temperature magnetization, are studied to understand the complete phase diagram. An interesting and potentially important feature of this model is that it can exhibit a macroscopic magnetization jump in the presence of a magnetic field; we study this using an effective Hamiltonian.
authors.affiliation: Solid State & Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India.
authors.forename: Shaon
authors.initials: S
authors.lastname: Sahoo
authors.forename: V M L
authors.initials: VM
authors.lastname: Durga Prasad Goli
authors.forename: Diptiman
authors.initials: D
authors.lastname: Sen
authors.forename: S
authors.initials: S
authors.lastname: Ramasesha
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D060526:Magnetic Fields; D008956:Models, Chemical; D011789:Quantum Theory; D013113:Spin Labels
chemical_list: D013113:Spin Labels