Loss of classicality in the alternating spin-½/spin-1 chain, in the presence of next-neighbor couplings and Dzyaloshinskii-Moriya interactions

Author(s):  
Abhiroop Lahiri ◽  
Swapan K Pati

Abstract We have considered and alternating spin-½/spin-1 chain with nearest-neighbor (J1), next-nearest neighbor (J2) antiferromagnetic Heisenberg interactions along with z-component of the Dzyaloshinskii-Moriya(DM) (Dz) interaction. The Hamiltonian has been studied using (a) Linear Spin-Wave Theory(LSWT) and (b) Density Matrix Renormalization Group (DMRG). The system had been reported earlier as a classical ferrimagnet only when nearest neighbor exchange interactions are present. Both the antiferromagnetic next-nearest neighbor interactions and DM interactions introduce strong quantum fluctuations and due to which all the signatures of ferrimagnetism vanishes. We find that the nonzero J2 introduces strong quantum fluctuations in each of the spin sites due to which the z-components of both spin-1 and spin-1/2 sites average out to be zero. The ground state becomes a singlet. The presence of J1 along with Dzintroduces a short range order but develops long range order along the XY plane. J1 along with J2induces competing phases with structure factor showing sharp and wide peaks, at two different angles reflecting the spin spiral structure locally as well as in the underlying lattice. Interestingly, we find that the Dz term removes the local spin spiral structure in z-direction, while developing a spiral order in the XY plane.

2001 ◽  
Vol 79 (11-12) ◽  
pp. 1581-1585 ◽  
Author(s):  
T Tonegawa ◽  
H Matsumoto ◽  
T Hikihara ◽  
M Kaburagi

The ground state of an Ising-type spin-1/2 chain with ferromagnetic bond-alternating nearest-neighbor and anti-ferromagnetic uniform next-nearest-neighbor interactions is studied by using the exact-diagonalization method and the density-matrix renormalization-group method. The Hamiltonian describing the system is expressed as H = – Σi h2i–1,2i – J1 Σi h2i,2i+1 + J2 Σi hi,i+2 with hi,i' = γ(Six Si'x + Siy Si'y) + Siz Si'z, where J1 [Formula: see text] 0, J2 [Formula: see text] 0, and 1 > γ [Formula: see text] 0. Special attention is paid to the ground-state phase diagram on the J1 versus J2 plane for a given value of γ. The phase diagram is composed of the ferromagnetic, intermediate, and up-up-down-down phases, the intermediate phase being characterized by its magnetization, which takes finite but unsaturated values. The phase diagram obtained for γ = 0.5 shows that the region of the intermediate phase for a given value of J1 is widest when J1 = 1.0 and becomes narrower rather rapidly as J1 decreases or increases from 1.0. The J2-dependence of the ground-state magnetization for γ = 0.5 and J1 = 0.85 is also discussed. PACS Nos.: 75.10Jm, 75.40Mg


2008 ◽  
Vol 22 (16) ◽  
pp. 2589-2597
Author(s):  
C. SRINITIWARAWONG ◽  
P. PUNPET

We have calculated the orbital correlation of the spinless two orbitals Hubbard chain in the limit of a very strong on-site Coulomb interaction and half-filling. The Hamiltonian is written in the form of pseudospin operators, and the Hilbert space is restricted to those states with only one electron per lattice site. The ground state wave function has been calculated using the density matrix renormalization group method. It has been found that the orbital correlations occur in the chain along the x-, y-, and z-axis and these are in antiferro-orbital states.


Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1933
Author(s):  
András Lászlóffy ◽  
Krisztián Palotás ◽  
Levente Rózsa ◽  
László Szunyogh

We present results for the electronic and magnetic structure of Mn and Fe clusters on Nb(110) surface, focusing on building blocks of atomic chains as possible realizations of topological superconductivity. The magnetic ground states of the atomic dimers and most of the monatomic chains are determined by the nearest-neighbor isotropic interaction. To gain physical insight, the dependence on the crystallographic direction as well as on the atomic coordination number is analyzed via an orbital decomposition of this isotropic interaction based on the spin-cluster expansion and the difference in the local density of states between ferromagnetic and antiferromagnetic configurations. A spin-spiral ground state is obtained for Fe chains along the [11¯0] direction as a consequence of the frustration of the isotropic interactions. Here, a flat spin-spiral dispersion relation is identified, which can stabilize spin spirals with various wave vectors together with the magnetic anisotropy. This may lead to the observation of spin spirals of different wave vectors and chiralities in longer chains instead of a unique ground state.


2001 ◽  
Vol 79 (11-12) ◽  
pp. 1587-1591 ◽  
Author(s):  
T Hikihara ◽  
M Kaburagi ◽  
H Kawamura

The ordering of the frustrated S = 1/2 XY spin chain with the competing nearest- and next-nearest-neighbor anti-ferromagnetic couplings, J1 and J2, is studied by using the density-matrix renormalization-group method. It is found that besides the well-known spin-fluid and dimer phases the chain exhibits a gapless "chiral" phase characterized by the spontaneous breaking of parity, in which the long-range order parameter is a chirality, κl =SxlSyl+1 – Syl Sxl+1, whereas the spin correlation decays algebraically. The dimer phase is realized for 0.33 [Formula: see text] j = J2/J1 [Formula: see text] 1.26 while the chiral phase is realized for j [Formula: see text] 1.26. PACS No.: 75.25


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