Magnetic Refrigeration and Spin-Lattice Relaxation in Gadolinium-Based Molecular Nanomagnets.
We review history, materials and underlying physics that form a background common to magnetic refrigeration and spin-lattice relaxation. To illustrate how these subjects are profoundly interrelated with each other, we describe studies performed on the molecular nanomagnets with formula [Gd(W5O18)(2)](9-) and [Gd(P5W30O110)](12-). Each molecular unit carries a single ion of gadolinium, which is coordinated to different polyoxometalate moieties, respectively. Each Gd3+ spin is magnetically isolated and maintains thermal equilibrium with the lattice down to temperatures close to absolute zero. For T less than or similar to 200 mK, the spin-lattice relaxation becomes dominated by pure quantum tunneling events. We discuss these properties with a keen eye for promising applications of molecular nanomagnets, namely, as magnetic refrigerants for attaining such low temperatures and spin qubits in quantum information processing.