Aggregate frequency width, nuclear hyperfine coupling and Jahn-Teller effect of Cu²⁺ impurity ion ESR in SrLaAlO₄ dielectric resonator at 20 millikelvin

The impurity paramagnetic ion, Cu²⁺ substitutes Al in the SrLaAlO₄ single crystal lattice, this results in a CuO₆ elongated octahedron, and the resulting measured g-factors satisfy four-fold axes variation condition. The aggregate frequency width of the electron spin resonance with the required minimum level of impurity concentration has been evaluated in this single crystal SrLaAlO₄at 20 millikelvin. Measured parallel hyperfine constants, A_∥Cu, were determined to be -155.7 × 10^-4 cm^-1, - 163.0 × 10^-4 cm^-1, - 178.3 × 10^-4 cm^-1 and -211.1 × 10^-4 cm^-1 at 9.072 GHz (WGH4,1,1) for the nuclear magnetic quantum number MI = +3/2 ,+1/2 ,-1/2 , and-3/2 respectively. The anisotropy of the hyperfine structure reveals the characteristics of the static JahnTeller effect. The second-order-anisotropy term, ≈ ( spin-orbit coupling/10Dq )², is significant and cannot be disregarded, with the local strain dominating over the observed Zeeman-anisotropy-energy difference. The Bohr electron magneton, - = 9.23 × 10^-24JT^-1, (within -0.43% so-called experimental error) has been found using the measured spin-Hamiltonian parameters. Measured nuclear dipolar hyperfine structure parameter P- = 12.3 × 10^-4 cm^-1 shows that the mean inverse third power of the electron distance from the nucleus is 〈r_q ^-3〉 ≲ 5.23 a.u. for Cu²⁺ ion in the substituted Al³⁺ion site assuming nuclear electric quadruple moment Q = -0.211 barn.