TRANSITION FROM A PARAMAGNETIC METALLIC TO A CLUSTER GLASS METALLIC STATE IN ELECTRON-DOPED PEROVSKITE MANGANITES

The study of Mn(IV)-rich manganites Ca1-xSmxMnO3 with low electron con tent corresponding to 0 less than or equal to x less than or equal to 0.12 demonstrates the large difference of their electronic and magneti c properties with that of Mn(III)-rich manganites. In particular, a me talliclike temperature dependence of the resistivity ((rho)) is observ ed above T-C, the smallest room-temperature rho = 10(-3) Omega cm bein g reached for x= 0.12. However increasing hopping energy with x sugges ts the creation of small polarons as e(g) electrons are injected into the Mn(IV) matrix. The thermopower (S) measurements confirm the increa se of carriers with x and can be described within a single-band metal model. The rho(T) and S(T) curves exhibit also a transition at a fixed temperature T(p)similar to 110 K for 0.075 less than or equal to x le ss than or equal to 0.12. T-p is related to the appearance of a ferrom agnetic component hs shown from T-dependent magnetization. Nevertheles s, the ac-chi measurements reveal a complex behavior. CaMnO3 exhibits a weak ferromagnetic component (T-C= 122 K) whereas for Ca1-xSmxMnO3 ( 0<x less than or equal to 0.12) the chi'(T) curves are characterized b y large bumps at T-m with T-m< T-C. Moreover, the shapes of the latter an found to be h(ac) dependent and T-m is also frequency dependent as shown from chi ''( T) curves. The magnetization measurements indicate a cluster glass state below T-C and demonstrate the lack of long-rang e ferromagnetism in these electron-doped manganites. [S0163-1829(98)03 529-2].