Growth and giant magnetoresistance effect in La-Ca-Mn-O and La-Sr-Mn-O single crystals

Bulk single crystals of La(1-x)A(x)MnO(3), where A = Ca, Sr and x = 0-0.33, were obtained by floating zone melting with radiation heating. The growth process was accompanied by evaporation of Mn, nevertheless, the boules obtained were single phase La(1-x)A(x)MnO(3), with Mn concentration being slightly less than stoichiometric. Upon replacing La with Ca, the Ca distribution coefficient rapidly decreased, reaching 0.57 for La0.67Ca0.33MnO3, whereas the Sr distribution coefficient was only slightly less than unity, even for a high degree of La substitution (La0.7Sr0.3MnO3). The GMR effect in La0.7Sr0.3MnO3 and La0.67Ca0.33MnO3 crystals was as high as 5% in 0.1 T (some 50% from the record value in thin films at the same magnetic field).