arXiv subjects

J. Abouie

Publications and source records attributed to J. Abouie.

21 records · Page 2Linked to original sources

arXiv2009

Factorized ground state for a general class of ferrimagnets

We have found the exact (factorized) ground state of a general class of ferrimagnets in the presence of a magnetic field which covers the frustrated, anisotropic and long range interactions for arbitrary dimensional space. In particular cases, our model represents the bond-alternating, ferromagnet-antiferromagnet and also homogeneous spin $s$ model. The factorized ground state is a product of single particle kets on a bipartite lattice composed of two different spins ($ρ, σ$). The spin waves analysis around the exact ground state show two branch of excitations which is the origin of two dynamics of the model. The signature of these dynamics is addressed as a peak and a broaden bump in the specific heat.

cond-mat.stat-mech↗

arXiv2006

Thermodynamic properties of the ferrimagnetic spin chains in the presence of a magnetic field

We have implemented three approaches to describe the thermodynamic properties of ferrimagnetic ($S=5/2, s=2$) spin chains. The application of cumulant expansion has been generalized to the ferrimagnetic chain in the presence of an external magnetic field. Using cumulants, we have obtained the field dependent effective Hamiltonian in terms of the classical variables up to the second order of quantum corrections. Thermodynamic functions, the internal energy, the specific heat and the magnetic susceptibility are obtained from the effective Hamiltonian. We have also examined the modified spin wave theory to derive the same physical properties. Finally, we have studied our model using quantum Monte Carlo simulation to obtain accurate results. The comparison of the above results and also the high temperature series expansion shows that cumulant expansion gives good results for moderate and high temperature regions while the modified spin wave theory is good for low temperatures. Moreover, the convergence regions of the cumulant expansion and the modified spin wave theory overlap each other which propose these two as a set of complement methods to get the thermodynamic properties of spin models.

cond-mat.str-el↗

arXiv2004

Cumulant expansion for ferrimagnetic spin (S_1, s_2) systems

We have generalized the application of cumulant expansion to ferrimagnetic systems of large spins. We have derived the effective Hamiltonian in terms of classical variables for a quantum ferrimagnet of large spins. A noninteracting gas of ferrimagnetic molecules is studied systematically by cumulant expansion to second order of ($Js/T$) where $J$ is the exchange coupling in each molecule, $s$ is the smaller spin ($S_1, s_2$) and $T$ is temperature. We have observed fairly good results in the convergent regime of the expansion, i.e $T > Js$. We then extend our approach to a system of interacting ferrimagnetic molecules. For one dimensional nearest neighbor interaction we have observed that the correlation of more than two neighboring sites is negligible at moderate and high temperature behavior. Thus the results of a single molecule can be applied to the chain of interacting molecules for temperatures greater than classical energy scale, i.e $T>JS_1s_2$. Finally we will discuss the effect of spin inhomogeneity on the accuracy of this method.

cond-mat.str-el↗