Magnetothermal properties of the Heisenberg-Ising orthogonal-dimer chain with triangularXXZclusters

Abstract

We study a spin-1/2 model with triangular XXZ clusters on the orthogonal-dimer chain in the presence of an external magnetic field. First, we discuss the case where the triangular clusters are coupled via intermediate "classical" Ising spins. Diagonalization of the triangular XXZ clusters yields the exact ground states; finitetemperature properties are computed exactly by an additional transfer-matrix step. A detailed analysis reveals a large variety of ground states at magnetization M equal to fractions 0, 1/4, and 1/2 of the saturation magnetization M = 1. Some of these ground states break translational symmetry spontaneously and give rise to doubling of the unit cell. In a second part, we present complementary numerical data for the spin-1/2 Heisenberg model on the orthogonal-dimer chain. We analyze several examples of T = 0 magnetization curves, entropy as a function of temperature T and magnetic field, and the associated magnetic cooling rate. Comparison of the two models shows that in certain situations the simplified exactly solvable model yields a qualitatively or sometimes even quantitatively accurate description of the more challenging quantum model, including a case which may be relevant to experimental observations of an enhanced magnetocaloric effect in the two-dimensional compound SrCu 2 (BO 3 ) 2 .

Thermodynamic properties of highly frustrated quantum spin ladders: Influence of many-particle bound states

“…The key physical property allowing such a straightforward approach is that the interaction between any two neighboring singlet and triplet rungs (and indeed between two singlet rungs) is precisely zero, so that rung and cluster states need only be placed side by side in all possible combinations. This type of strategy has been applied previously [74][75][76] to models with local conservation laws [66,[77][78][79][80][81], including to the fully frustrated ladder [74], where the calculations were restricted to systems up to L = 12 (24 spins). Here we extend this treatment to L = 14, a value that we note lies beyond the limit of 24 S = 1/2 spins accessible in conventional full- diagonalization calculations, even for systems with high spatial symmetry [33].…”

Normal and inverse magnetocaloric effect in magnetic multilayers with antiferromagnetic interlayer coupling

“…Also, MCE in vicinity of the compensation temperature has been a subject of studies 63 . We mention that the coexistence of normal and inverse MCE is in general possible in a class of magnets exhibiting rich structure of the ground-state phase diagram, in particular in Ising-Heisenberg chains [23][24][25][26][27][28][29][30][31] or even some zero-dimensional structures 64 . However, we consider the multilayer geometry to be of particular interest.…”

Fractional magnetization plateaus of the spin-12Heisenberg orthogonal-dimer chain: Strong-coupling approach developed from the exactly solved Ising-Heisenberg model

“…To this end, we have performed the DMRG computation using ALPS package 57 for the systems of N = 128. It should be noted that an analogous numerical approach was used for the orthogonal-dimer chain with triangular clusters 58 .…”