Metastable diamagnetism in the manganite Sm0.1 Ca0.84 Sr0.06 MnO3

Magnetic properties of polycrystalline Sm0.1 Ca0.84 Sr0.06 MnO3 in pristine and metastable states have been investigated in wide range of temperatures and magnetic fields. It was found that below Curie temperature TC ≈105 K the pristine state exhibits phase separation comprising ferromagnetic and antiferromagnetic phases. The metastable states with reduced magnetization were obtained by a successive number of quick coolings of the sample placed in a container with a kerosene-oil mixture. By an increasing number of quick coolings (>6) the long time relaxation appeared at 10 K and the magnetization reversed its sign and became strongly negative in a wide temperature range, even under an applied magnetic field of 15 kOe. The observed field and temperature dependences of the magnetization in this state are reversed in comparison with the ordinary ferromagnetic ones. Above TC, the observed diamagnetic susceptibility of the reversed magnetization state at T=120 K is χdia ≈-0.9× 10-4 emu g-1 Oe-1. Only after some storage time at room temperature, the abnormal magnetic state is erasable. It is suggested that the negative magnetization observed results from a specific coupling of the nano/microsize ferromagnetic regions with a surrounding diamagnetic matrix formed, in a puzzled way, by the repeating training (quick cooling) cycles.