Determination of antiferromagnetic coupling constants in the spin-dimer compound β-Sr2Cu(BO3)2

Electron Spin Resonance was used to study the spin-dimer compound β-Sr2Cu(BO3)2. The value of the antiferromagnetic coupling constant (J) between the copper dimers was estimated from temperature-dependence measurements to be 92 K at a frequency of 111.3 GHz and 91 K at a frequency of 66.7 GHz. Introduction From refrigerator magnets to hard drives, magnetism is a familiar phenomenon. The source of the unique behavior of everyday magnetic materials is the spontaneous, parallel alignment of unpaired electron spins on neighboring atoms. This type of magnetism is called ferromagnetism. An equally common yet very different form of magnetism is antiferromagnetism. Like ferromagnetism, antiferromagnetism arises due to the spontaneous alignment of unpaired electron spins on neighboring atoms, but the alignment of spins in antiferromagnetic materials is anti-parallel. In both ferromagnetic and antiferromagnetic (AF) spin systems, exchange interactions cause spontaneous spin alignment. A purely quantum-mechanical phenomenon, exchange occurs when the wavefunctions of two or more fermions, particles having half-integer spins, overlap; this results in a change in the fermions’ energies. The term describing exchange