Magnetically two-phase state in Eu(1-x)A(x)MnO(3) (A = Ca, Sr)

It is observed that low-temperature magnetic properties (dependence of the magnetization on the cooling conditions and the presence of a maximum in th e initial magnetic susceptibility) of Eu(1-x)A(x)MnO(3) (A=Ca, Sr; x=0,0.3) samples are similar to those of spin glasses. However, there are also subs tantial differences: The magnetization depends on the cooling conditions ri ght up to the maximum measurement fields H=45 kOe, and the temperature of T -N of the maximum of the initial magnetic susceptibility is independent of the frequency of the ac magnetic field in which the susceptibility is measu red. The magnetization isotherms for T less than or equal to T-N are a supe rposition of a linear part, characteristic for an antiferromagnet, and a sm all spontaneous part. For compositions containing Sr a maximum of the resis tivity rho (rho(max) similar to 108 Ohm . cm) is observed near T-N ; in a 1 20 kOe magnetic field this maximum is lowered by four orders of magnitude a nd the temperature of the maximum is two times higher. In compositions with x=0.3 the paramagnetic Curie point is much higher than for the composition with x=0: theta=110 K (A=Ca), 175 K (A=Sr), and -100 K (x=0). These charac teristic features of the magnetic and electric properties are explained by the existence of a magnetically two- phase state in this system, consisting of ferromagnetic clusters, in which the charge carriers are concentrated, embedded in an insulating antiferromagnetic matrix. (C) 1999 American Insti tute of Physics. [S0021-3640(99)00805-1].