EPR Study of Monoclinic RbD$\text{}_{2}$PO$\text{}_{4}$ Monocrystal Doped with Cr$\text{}^{5+}$ Ion

Deuterated monoclinic RbD$\text{}_{2}$PO$\text{}_{4}$ (DRDP) doped with chromium Cr$\text{}^{5+}$ is studied by EPR in 90 K to 400 K temperature range. EPR reveals two types of paramagnetic centers: single Cr$\text{}^{5+}$ (S = 1/2) complex and Cr$\text{}^{5+}$-Cr$\text{}^{5+}$ coupled pairs with effective spin S = 1. The EPR line splitting of single Cr$\text{}^{5+}$ complex in DRDP versus temperature agrees with the unit cell multiplication. The splitting of EPR line of pair spectrum appears at T* = 160 K, far below the phase transition temperatures and is due to the anisotropy of the exchange interaction. The clustering effect in the low-dimensional DRDP is suggested.