In this research, we propose a model of an impurity nitrogen center in tricalcium phosphate (TCP). This impurity was not intentionally added but was detected by electron paramagnetic resonance (EPR). It was shown that the EPR spectrum of the powder under study is due to two types of such impurity centers, which we attribute to the TCP phase and the admixed hydroxyapatite phase. The parameters of the spin Hamiltonian for the center in TCP obtained using Density Functional Theory (DFT) calculations are close to the experimental ones and allow us to propose a model of a nitrogen-containing center. The temperature dependence of the spin-lattice relaxation rate in the TCP phase is described by a process proportional to T^2.35 in the temperature range from 10 to 300 K

The magnetic system of the Li₂CuCrO₄ compound is characterized by the formation of helical spin structures in CuO₂ chains due to strong frustrations of the exchange interaction. The double position of lithium ions determines the existence of the dielectric glass state at T<=70 K. In this work, using the NMR technique, we found the activation energy of the dipole glass system E_a = 101 K and determined the type of helicoidal copper spin structure as a "screw". It was demonstrated how the high-temperature interaction of strongly correlated spin and dielectric subsystems in this compound paradoxically prevents the appearance of multiferroic behavior in the ordered phase

The low-cost device for optical detection of magnetic resonance (ODMR) has been developed for use with commercial electron paramagnetic resonance spectrometers. The equipment is based on a scheme with coaxial optical fibers, where the excitation is transmitted through a central fiber with a diameter of 400 μm, and the photoluminescence signal is collected using seven optical fibers with a diameter of 200 μm. The device has the ability to modulate the excitation radiation, microwave frequency and magnetic field. The ODMR attachment has been tested on standard and well-known NV ^- (nitrogen-vacancy) paramagnetic centers in diamonds. ODMR experiments were carried out in the X-band (9.4 GHz) frequency range with a magnetic field B₀ sweeping from 220 to 470 mT. The best signal-to-noise ratio was obtained by modulating of the magnetic field

We present the results of the quantum calculation of the ground state energies and magnetic g-factors of two rare earth (RE) ions: Yb³⁺ in Y₂Ti₂O₇ crystal and Er³⁺ in YPO₄ crystal. The Variational Quantum Eigensolver (VQE) algorithm has been performed on 5-qubit IBM superconducting quantum computers via IBM Quantum Experience cloud access. The Hamiltonian of the lowest spectroscopic multiplet of each RE ion, containing crystal field and Zeeman interaction, has been projected onto the collective states of three (Yb³⁺) and four (Er³⁺) coupled transmon qubits. The lowest-energy states of RE ions have been found by minimizing the mean energy in ∼ 250 - 350 iterations of the algorithm: the first part was performed on a quantum simulator, and the last 25 iterations were conducted on the real quantum computing hardware. All the calculated ground-state energies and magnetic g-factors agree well with their exact values, while the estimated error of 2÷15% is mostly attributed to the decoherence associated with the two-qubit operations