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Register a new userProperties of highly frustrated magnetic molecules studied by the finite-temperature Lanczos method
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The very interesting magnetic properties of frustrated magnetic molecules are often hardly accessible due to the prohibitive size of the related Hilbert spaces. The finite-temperature Lanczos method is able to treat spin systems for Hilbert space sizes up to 10^9. Here we first demonstrate for exactly solvable systems that the method is indeed accurate. Then we discuss the thermal properties of one of the biggest magnetic molecules synthesized to date, the icosidodecahedron with antiferromagnetically coupled spins of s=1/2. We show how genuine quantum features such as the magnetization plateau behave as a function of temperature.
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We discuss the magnetocaloric properties of gadolinium containing magnetic molecules which potentially could be used for sub-Kelvin cooling. We show that a degeneracy of a singlet ground state could be advantageous in order to support adiabatic processes to low temperatures and simultaneously minimize disturbing dipolar interactions. Since the Hilbert spaces of such spin systems assume very large dimensions we evaluate the necessary thermodynamic observables by means of the Finite-Temperature Lanczos Method.
It is virtually impossible to evaluate the magnetic properties of large anisotropic magnetic molecules numerically exactly due to the huge Hilbert space dimensions as well as due to the absence of symmetries. Here we propose to advance the Finite-Temperature Lanczos Method (FTLM) to the case of single-ion anisotropy. The main obstacle, namely the loss of the spin rotational symmetry about the field axis, can be overcome by choosing symmetry related random vectors for the approximate evaluation of the partition function. We demonstrate that now thermodynamic functions for anisotropic magnetic molecules of unprecedented size can be evaluated.
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We theoretically study finite temperature properties of interacting fermion systems under geometrical frustration in the charge degree of freedom. Physical quantities such as charge structure factors, the specific heat, and the entropy, of the two-dimensional model of interacting spinless fermions on an anisotropic triangular lattice are numerically calculated using the thermal pure quantum state. By considering the Coulomb interactions up to the next-nearest-neighbor bonds, we elucidate that in the highly frustrated region where a long-period stripe-type charge order (CO) is the ground state, fluctuations of different stripe-type CO patterns become large at finite temperatures. When we further introduce $1/r$-type long-range Coulomb interactions, the ground state unexpectedly recovers the non-stripe-type 3-fold CO pattern characteristic of triangular lattice models with short-range interactions. Our results imply that the BEDT-TTF-based organic conductors exhibiting glass-like behavior locates in the region of the intermediate strength of long-range interactions, where both the stripe- and non-stripe-type CO fluctuations are prominent.
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