Probing the magnetic state by linear and non linear ac magnetic susceptibility measurements in under doped manganite Nd0.8Sr0.2MnO3

摘要

We have thoroughly investigated the entire magnetic states of under dopedferromagnetic insulating manganite Nd0.8Sr0.2MnO3 through temperature dependentlinear and non linear complex ac magnetic susceptibility measurements. Thisferromagnetic insulating manganite is found to have frequency independentferromagnetic to paramagnetic transition temperature at around 140 K. At around90 K (\approx T_f) the sample shows a second frequency dependent re - entrantmagnetic transition as explored through complex ac susceptibility measurements.Non linear ac susceptibility measurements (higher harmonics of acsusceptibility) have also been performed (with and without the superposition ofa dc magnetic field) to further investigate the origin of this frequencydependence (dynamic behavior at this re-entrant magnetic transition).Divergence of 3rd order susceptibility in the limit of zero exciting fieldindicates a spin glass like freezing phenomena. However, large value of spinrelaxation time (?0= 10-8 s) and small value of coercivity (~22 Oe) obtained atlow temperature (below T_f) from critical slowing down model and dc magneticmeasurements, respectively, are in contrast with what generally observed in acanonical spin glass (?0 = 10-12 - 10-14 s and very large value of coercivitybelow freezing temperature). We have attributed our observation to theformation of finite size ferromagnetic clusters which are formed as consequenceof intrinsic separation and undergo cluster glass like freezing below certaintemperature in this under doped manganite. The results are supported by theelectronic - and magneto - transport data.