Relaxation of magnetic clusters in Sr and Fe doped cobaltate perovskites

Mossbauer study of La1 − x Sr x 57Fe0.025Co0.975O3 (0.15 ≤ x ≤ 0.25) perovskites below their magnetic ordering temperature shows cooperative electronic and magnetic phase separation for all compositions investigated. It is shown that the increase of the Sr concentration results in a transition from superparamagnetism to long range ferromagnetism of Co clusters between x = 0.18 and 0.2. In-field Mossbauer measurements revealed the existence of frustrated magnetic interactions at x = 0.22.