Metamagnetic transition in the system Eu1-xSrxMn0.5Co0.5O3 (0 ≤ x ≤ 0.75)

Magnetic properties of orthorhombic (space group Pnma) perovskite EuMn0.54+Co0.52+O3 synthesized at various temperatures are studied up to 140 kOe. The sample obtained at 1500 °C shows a metamagnetic behavior irreversible below 40 K, whereas the sample obtained at 1200 °C exhibits purely ferromagnetic behavior. Both samples are ordered at Curie temperature TC = 123 K and reach equal magnetizations at high magnetic fields. The substitution of Eu3+ by Sr2+ within Eu1-xSrxMn0.5Co0.5O3 series of compounds leads to the increase in TC, but the magnetization of these compositions strongly decreases and the metamagnetic transition disappears at x > 0.3. The composition with x = 0.75 is a cubic (Pm3¯m) antiferromagnet with Neel temperature TN ≈ 210 K. It is assumed that the metamagnetic transition is associated with a transition from a noncollinear into a collinear ferromagnetic phase. A noncollinear phase is formed due to the competition between positive Co2+ - Mn4+ and negative Mn4+ - Mn4+ and Co2+ - Co2+ superexchange interactions in the presence of large magnetic anisotropy. It is suggested that Sr2+ doping leads to formation of mixed high/low spin state of Co3+ ions and enforces antiferromagnetic component.