same way the transitions D − → D + are also suppressed. Thus the resistance increases as a result of application of external magnetic field. In our case of p-type structures the situation appears, again, more complicated due to more complex structure of A + centers. However, in general, the considerations given in [9], [10] still hold. Basing on the calculations similar to given in [10] one obtains for weak field limit µgH < T the following estimate: while g$_{l}$ , g$_{u}$ are the densities of states of the lower and upper Hubbard bands. Note that for the low concentration of dopants g$_{u}$ is controlled by the concentration of A + centers while g$_{l}$ - by the concentration of A − centers and thus g$_{l}$ = g$_{u}$ . At stronger magnetic fields when µgH > T , the corresponding contribution to magnetoresistance still increases with magnetic field increase until µgH reaches the value ξT and then saturates [9], [10]. One notes that at low enough temperatures the positive magnetoresistance of the spin nature suggested in [9] can exceed the wave shrinkage magnetoresistance. At the same time this contribution at relatively weak fields when µgH < T is expected to be comparable to the spin magnetoresistance resulting from interference term discussed above. Summarizing the both spin contributions to quadratic magnetoresistance we estimate the coefficient k resulting from the similar parametrization of the positive quadratic and linear negative magnetoresistance as was done above: Thus, as it is seen, for the Mott case at T → 0 k ∝ T 1 / 3 while for the ES case it is ∝ T 1 / $^{4}$. Note that in our calculations we assumed that the value of H$_{min}$ still corresponds to linear behavior of negative magnetoresistance which means that the magnetic flux through the interference area is much less than magnetic flux quantum Φ$_{0}$. The critical field H$_{sat}$ 14 k$_{2}$ = g$_{M}$E$_{B}$r 1 / 2 $_{min}$r$_{h}$ 2 a 1 / $^{2}$β Mott law k$_{2}$ = κ 2 e $_{4}$E 2 $_{B}$r$_{min}$ r 1 / 2 h 2 a 1 / $^{2}$β ES law β = P ( H = 0) T gµ$_{B}$ r 3 / 2 h a 1 / $^{2}$e c ¯ h ( CF + α Δ R$_{sat}$ R (0) ) − 1 / 2 (34) F = 2 g$_{l}$g$_{u}$ ( g$_{l}$ + g$_{u}$ ) 2 (33) ln R ( H ) R (0) = CF ( gµ$_{b}$H T ) 2 (32) where C ∼ 1 / 3,