Evolution of baryonic matter temperature T_b (solid lines) and spin temperature T_s (dotted lines) from cosmological recombination up to z = 10 in ΛCDM model with PMF with different B₀ (left panel) and with different values of spectral indices n_B (right panel). The dashed line in both panels shows the temperature of CMB. The inset in the right panel shows T_b(z, B₀, n_B)/T_b(z, B₀, n_B = −2.9) for the purpose of distinguishing lines in the 21 cm line formation region.