METAL-INSULATOR-TRANSITION INDUCED BY A MAGNETIC-FIELD IN THE COMPOUNDS EU(0.7)A(0.3)MNO(3) (A = CA, SR)

The temperature R(T) and field R(H) dependences of the electrical resi stance in the compound Eu(0.7)A(0.3)MnO(3) (A = Ca, Sr) are investigat ed in the temperature range 4.2-200 K in magnetic fields up to 14 T. A bove the antiferromagnetic transition temperature T-a, the function R( T) is semiconducting in character. Application of a magnetic field H t hat exceeds a certain critical value H-c changes the character of the function R(T) for Eu0.7Sr0.3MnO3 to metallic (dR/dT>0). For T<T-a and H<H-c a jump in the resistance is observed indicating instability of t he electronic state caused by competition between charge and spin orde ring of the Mn ions of different valences. (C) 1998 American Institute of Physics.