Abstract
Effects of a single-ion anisotropy on magnetocaloric properties of selected spin-s≥1 antiferromagnetic Ising clusters with frustration-inducing triangular geometry are studied by exact enumeration. It is found that inclusion of the single-ion anisotropy parameter D can result in a much more complex ground-state behavior, which is also reflected in a magnetocaloric effect (MCE) at finite temperatures. For negative D (easy-plane anisotropy) with increasing s, the ground-state magnetization as a function of the external field gradually shows increasing number of plateaus of various heights. Except for the cases of integer s with D<D0≤0, the first magnetization plateau is of non-zero height. This property facilitates an enhanced MCE in the adiabatic demagnetization process in the form of an abrupt decrease in temperature as the magnetic field vanishes to zero. The cooling rate can be considerably enhanced in the systems with larger s and D>0 (easy-axis anisotropy), albeit its dependence on these parameters is strongly dependent on the cluster geometry. From the studied systems more favorable conditions for observing a giant MCE were found in the 2CS cluster, consisting of two corner-sharing tetrahedra, the experimental realization of which could be technologically used for efficient refrigeration to ultra-low temperatures.
Highlights
Molecular nanomagnets often occur in nature and nowadays owing to new technologies can be artificially prepared in a highly controlled manner [1,2,3]
We studied effects of the single-ion anisotropy on the ground-state and thermodynamic properties in two selected spin-s antiferromagnetic Ising spin clusters with geometrical frustration focusing on magnetocaloric effect (MCE)
The presence or absence of the zero-magnetization plateau is crucial for defining the character of the low-temperature MCE in the adiabatic demagnetization process
Summary
Molecular nanomagnets often occur in nature and nowadays owing to new technologies can be artificially prepared in a highly controlled manner [1,2,3] They can be viewed as zero-dimensional magnetic structures composed of small spin clusters, which are magnetically isolated from the environment. The spin degeneracy gradually increases with the spin number and further increases can be achieved by designing very weak magnetic links between the single-ion spin centers [13]. Another aspect that can result in a high degeneracy at low temperatures is geometrical frustration. Compared to paramagnetic salts, which are considered standard refrigerant materials for magnetic cooling, they were theoretically predicted [14,15] and experimentally confirmed, for example, on a pyrochlore lattice compound Gd2Ti2O7 [16], to show more than an order of magnitude bigger rate of the temperature decrease due to the varying of the external magnetic field
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
