Effects of disorder on magnetic, transport properties and high field-induced metamagnetic transition of La0.5Sr0.5Mn1-xM'xO3 (M' = Ga, In)

We have studied the influences of Mn-sites substitution on the charge ordered antiferromagnetic phase and pulsed high magnetic field-induced metamagnetic transition of La_0.5Sr_0.5Mn_1-xM'_xO₃ (M' = Ga, In, and 0 ≤ x ≤ 0.2). Both types of doping destroyed the long range charge ordered antiferromagnetic and ferromagnetic ordering, and caused a disordered state, thus phase separated and cluster/spin-glass like states were identified. The metamagnetic transition is driven by the application of pulsed high magnetic field up to 50 T, which gives an evidence of irreversible phase transition from antiferromagnetic short range ordering to ferromagnetic ordering. The analysis of temperature and magnetic field dependent resistivity suggests that the density of states at the Fermi level decreases with increasing Ga³⁺/In³⁺ doping concentration, which contributes to the insulating state. Both Ga³⁺ and In³⁺ ions are nonmagnetic (diamagnetic) ions and should not introduce any additional magnetic exchange interaction with substituting Mn³⁺. However, the Ga³⁺ and In³⁺ impurities directly substituting Mn³⁺ dilute the magnetic exchange interactions between Mn³⁺ and Mn⁴⁺ ions, especially the double exchange interaction through Mn³⁺-O^2--Mn⁴⁺ network is disarranged, and multiple magnetic interactions compete and coexist in the system, leading to the disordered state in Ga³⁺/In³⁺-doped compounds. Moreover, combined with the noticeable structure effects caused by the decrease of e_g electron band width, the In³⁺-doped system exhibits a much more disordered state.