Effect of magnetic exchange interactions in La(Sr)MnO3/LaMO3 (M = Fe, Cr, Co, Ni) artificial superlattices and their magnetic/electrical properties

We have fabricated conductive-ferromagnetic [(La0.8Sr0.2)MnO3/antiferromagnetic-[LaFeO3] spin-frustrated superlattices and insulative-ferromagnetic [La1-deltaMnO3]/magnetic [LaMO3] (M=Ni,Co,Cr,Fe) superlattices through accurate unit cell control (1-10 units) using a laser-molecular beam epitaxy technique. In [(La,Sr)MnO3](m)/[LaFeO3](n) superlattices, it has been observed that resistivity is increased and T-C is reduced from 270 to 130 K when the antiferromagnetic layer is increased. Metal-insulator transition occurred systematically in a series of superlattices (m=2) with n increasing from 1 to 3 unit cells. This can be explained by spin frustration induced by the neighboring antiferromagnetic spin order. This colossal magnetoresistance effect is enhanced by up to 35% in a magnetic field of 1.0 T. In [LaMnO3](1)/[LaMO3](1) superlattices, reduction (M=Cr,Fe) and enhancement (M=Co,Ni) of T-C have been observed. We propose an expression for T-C on the basis of the molecular field image and demonstrate that the ferromagnetism is systematically affected by the neighboring magnetic layers via the interface. (C) 2000 American Institute of Physics. [S0021-8979(00)05815-1].