Detailed neutron study of the crossover from long-range to short-range magnetic ordering in (Nd1−xTbx)0.55Sr0.45MnO3 manganites

12 pages, 12 figures, 2 tables.-- PACS number(s): 75.30.Kz, 75.47.Gk, 71.30.+h
We have applied three complementary neutron techniques (neutron diffraction, neutron depolarization, and small-angle neutron scattering) to investigate the crossover from long-range to short-range magnetic ordering in (Nd1−xTbx)0.55Sr0.45MnO3 manganite compounds. The obtained results indicate that the ground state at T=1.5 K is a long-range C-type canted ferromagnetic state for 0x(Tb)0.5 with ferromagnetic domains larger than several hundreds of nm that decrease as the Tb content increases. In the concentration range 0.5x(Tb)0.6, the ferromagnetic domain size decreases below ~100 nm and these large ferromagnetic clusters coexist in this concentration range with smaller short-range ferromagnetic clusters (around one nanometer size). For x(Tb)0.6, only short-range ferromagnetic and A-type and C-type antiferromagnetic clusters are present and their size is below ~5 nm. The obtained results are discussed in the context of the global phase diagram recently discussed for RE0.55Sr0.45MnO3 and in the context of the quantum critical point features recently suggested in manganites.
Financial support by the Spanish Ministry of Science (through projects SAB2003-0255, MAT2002-04657, and MAT2005-05565-C02-02 including FEDER funding), by the European Project SCOOTMO and by the Aragon Regional Government (through project E26) is acknowledged.