Magnetic structure and ordering of Nd ions in Ga substituted NdBa2Cu3O7 (abstract)

Abstract

Magnetic ordering of Nd3+ ion changes with oxygen concentration in NdBa2Cu3O7−x. In the oxygen-rich sample NdBa2Cu3O6.9, Nd3+ ion orders antiferromagnetically with 2D-Ising type of ordering. Whereas, in the oxygen reduced compound NdBa2Cu3O6.2 Nd ion orders three dimensionally at 1.73 K. Similar effects has been observed by specific heat measurements performed on NdBa2Cu3−yGayO7 (0<y<0.5). In these samples, a small amount of Ga substitution changes the magnetic ordering of Nd ions from 2D Ising (y=0) to 1D or magnetic clusters (y=0.01, 0.03). With higher Ga substitution, the third magnetic ordering is restored. The magnetic ordering seen in NdBa2Cu3−yGayO7 (y=0.5) is more isotropic in nature compared to NdBa2Cu3O6.2. The critical exponent derived from the specific data show a 3D spherical type of ordering. Magnetic neutron diffraction are performed at low and high temperatures for y=0.5 to deduce the magnetic structure, which are compared with the unsubstituted compounds and to verify the isotropic nature. The second-order CEF parameter A02 decreases for NdBa2Cu3−yGayO7 (y=0.5) which in turn reduces the magnetic anisotropy constant, consistent with magnetic specific heat results.