The technique of detecting electron paramagnetic resonance and measuring paramagnetic relaxation times at liquid-helium temperatures by the magneto-optical Faraday rotation has been applied to the even number (4f2) electron system of Pr3+ in praseodymium ethylsulphate (PrES). The EPR spectrum (X band) of undiluted PrES at 1.37 °K is a broad band extending over several kilo-gauss with no evidence of hyperfine structure. The band intensity decreases at [Formula: see text] and covers [Formula: see text] from its maximum to half-power point. The absence of any hyperfine structure indicates that crystal-field distortion is the main source of line broadening.The relaxation times measured as a function of temperature over the range 1.40 to 2.18 °K and at 4.22 °K range from 0.1 to 10 msec. For [Formula: see text], τ decreases from 0.40 to 0.15 msec, is proportional to T−(3.5 ± 0.6), and is considered to be the phonon–bath relaxation time. Values of τ show a scatter within 0.20 ± 0.02 msec for [Formula: see text]. Near the λ point [Formula: see text], τ exhibits a very rapid increase, having a value of 0.20 msec at 2.155 °K and 0.85 msec at 2.165 °K. This behavior appears to be related to the energy exchange between the crystal and liquid-helium bath. Measurements of τ at 2.18 °K and 4.22 °K indicate that the rate at which the spin–phonon system returns to initial thermal equilibrium is governed by the thermal conductivity of the liquid-helium bath.
Сверхтонкое и квадрупольное взаимодействия в ЭПР изотопов -=SUP=-153-=/SUP=-Eu-=SUP=-2+-=/SUP=- и -=SUP=-151-=/SUP=-Eu-=SUP=-2+-=/SUP=- в иттрий-алюминиевом гранате