On-line Ultrasonic Characterisation of bulk and Nano La1-xSrxMnO3 perovskite manganite materials K. Sakthipandi, N. R. Dhineshbabu, and V. Rajendran , Centre for Nanoscience and Technology, K.S.R College Of Technology, Thiruchengode, Namakkal (Dt) -637 215, Tamilnadu, India. Abstract La1-xSrxMnO3 perovskite magnetic materials with two different compositions namely x = 0.35 and 0.37 both at bulk and nano scale were prepared by solid state reaction and sonochemical reactor method respectively. The evaluation of magnetic phase transition temperature of prepared bulk and nano samples was made through on-line ultrasonic velocity and attenuation measurements. An indigenously designed experimental set-up has been employed for on-line ultrasonic velocities and attenuation measurement over a wide range of temperatures for 300 to 400 K. The observed anomalous lattice softening behaviour in the ultrasonic parameters was used to explore the phase transition temperature (Curie temperature TC) i.e., from paramagnetic (PM) to ferromagnetic (FM) phase transition both in bulk and nanostructured perovskite samples. Further, the ultrasonic measurements confirmed that sharp and broad transitions occur respectively in bulk and nanostructured perovskite manganite materials. The Curie temperature for nanoperovskite sample was lower than corresponding bulk perovskite sample, which was clearly identified by ultrasonic measurement. The variation in the magnitude of the ultrasonic parameter at the transition temperature was used to reveal the role of Sr content on phase transition both in bulk and nano perovskites.
Introduction
Indigenously designed Furnace A - Receiver Transducer (TS) G – Heating Chamber B –Sender Transducer (TR) H Temperature Sensor C – Water Cooling arrangement I – Sample E – Wave Guide J – Insulation plate F – Heater Coil K – Spring Load arrangements
Potential applications Unique physico-chemical Giant magneto Highest value High
resistance
Ultrasonic velocity measurements High power ultrasonic Pulser Receiver Digital storage oscilloscope (DSO) ULand αL measurements Frequency - 5 MHz
of Curie temperature (TC)
spin polarisation of charge carriers
Experimental Procedure Bulk : Solid State Reaction Method Bulk (BLSMO35 and BLSMO37)
Fig 1: Schemitic diagram
Preheated up to 873 K Pressed into Pellet Sintered – 1273 K Fig 4: XRD Analysis
Fig 3: TEM image
Table 1:Particle size
Fig 2: SEM image
Table 2:Ultrasonic studies Fig 6: Ultrasonic UL Fig 5: Ultrasonic αL Conclusion Reduced in the co-ordination Broken exchange bonds Origin of a spin-disordered magnetic state Prevent the formation of long-range charge ordered state Transition is suppressed Wide range of exchanges interactions Broad Transition Electron-lattice interactions in the LSMO Singleion (linear) magnetostriction Linear magnetostriction effect both in BLSMO and NLSMO samples Jahn–Teller distortion of the Mn3+O6 octahedral Bond length and bond angle of Mn-O-Mn bond causes more changes than the bulk perovskite samples