In this paper, a composed A + B magnetic system, with spins JA = 2 and JB = 3/2, is considered within the mean-field approximation, in the framework of Tsallis nonextensive statistics. Our motivation is twofold: (1) to approach the existing experimental data of manganese oxides (manganites), where Mn3+ and Mn4+ form two magnetic sublattices, and (2) to investigate the structure of nonextensive density matrices of composed systems. By imposing that thermodynamic quantities, such as the magnetization of sublattices A and B, must be invariant whether the calculation is taken over the total Hilbert space or over partial subspaces, we found that the expression for the nonextensive entropy must be adapted. Our argument is supported by the calculation of sublattice magnetizations MA and MB, internal energy, UA and UB and magnetic specific heat, CA and CB. It is shown that only with the modified entropy, the two methods of calculation agree to each other. Internal energy and magnetization are additive, but no clear relationship was found between SA, SB and the total entropy SA+B for q /= 1. It is shown that the reason for the failure of the standard way of calculation is the assumption of statistical independence between the two subsystems, which however does not affect the density matrix in the full Hilbert space.Razmatramo magnetski sustav složen od sastavnica A i B sa spinovima JA = 2 i JB = 3/2 u približenju srednjeg polja i Tsallisove nesveobuhvatne statistike. Dva su povoda: (1) opisati poznate mjerne podatke za manganove okside (manganite), u kojima Mn3+ i Mn4+ tvore dvije magnetske podrešetke, i (2) istražiti strukturu nesveobuhvatne matrice gustoće složenih sustava. Postavljajući da termodinamičke veličine, kao magnetizacija podrešetaka A i B, moraju biti invarijantne kako za račun u cijelom Hilbertovom prostoru, tako i u pojedinim podrešetkama, nalazimo da se izraz za nesveobuhvatnu entropiju mora primijeniti. Naša tvrdnja se zasniva na računu magnetizacije podrešetaka MA i MB, unutarnje energije UA i UB, i magnetske specifične topline, CA i CB. Pokazuje se da su s izmijenjenom entropijom obje metode u skladu. Unutarnja energija i magnetizacija se pribrajaju, ali između SA, SB i ukupne entropije SA+B nismo našli jednostavan odnos za q /= 1. Pokazuje se da je pretpostavka o neovisnosti dvaju podsustava razlog što uobičajen način računanja entropije nije dobar, što ne utječe na račun matrice gustoće u cijelom Hibertovom prostoru
