Projects
Activities
Sites and dynamics of hydrogen (deuterium) in metal hydrides (deuterides)
Effect of hydrogen on electronic properties of metals
Structure and magnetic properties of topologically frustrated systems
Spin state transition and magneto-electronic phase separation in doped rare-earth perovskites
Electronic properties of intermetallic Kondo and heavy fermionic compounds
Electronic properties of quasi one- and two-dimensional oxide materials
Evolution of ball-milled alloys
Ongoing Research Projects
1. 27A1 NMR studies in grain aligned CeNi2A15 and LaNi2A15
Detailed 27A1 NMR studies have been performed in CeNi2A15 and compared with those of isostructural LaNi2A15 in 7 tesla and in the temperature range 3.5-300 K. CeNi2A15 is a dense Kondo compound which orders antiferromagnetically at 2.6 K. For the two inequivalent Al sites in this compound, the nuclear quadrupolar splitting frequency nQ are 0.98 and 2.52 MHz. Knight shifts for both the sites are almost equal in magnitude and follow a linear relation with the molar susceptibility in the range 30-300 K. The transferred hyperfine coupling constant Hhf = 1.84 kOe/mB is small compared to those in other Ce compounds. The behaviour of 1/T1f for the two Al sites are widely different. For Al(1) site with one nearest neighbour Ce ion, the Ce-4f electron spin fluctuation process dominates over the Korringa contribution in relaxation below about 150 K. Such type of relaxation behaviour was observed for 27A1 nuclear spin-lattice relaxation in the well-known Kondo compound CeA12. On the other hand, in the relaxation of 27A1 nuclei in A1(2) site, which is in between two Ce near neighbours, the effect of spin fluctuation due to Kondo effect overcomes that due to the RKKY interaction in the range 12-300 K. These widely different mechanisms in the nuclear spin lattice relaxation processes of two inequivalent Al sites over a large temperature range is an interesting observation in a dense Kondo system which exhibits magnetic ordering.
2. 51V NMR study in quasi-one dimensional alternating chain compound BaCu2V2O8
51V NMR studies in a polycrystalline sample of BaCu2V2O8 reveal the existence of non-zero spin densities, with unequal magnitudes, at the two vanadium sites viz., V(1) and V(2) and hence the participation of VO4 tetrahedra to the intra-chain and inter-chain exchange interaction. The behaviour of Kiso below 200 K provide a clear signature of the reduction of Cu2+ spin susceptibility within the chain. Furthermore, there exist different hyperfine coupling constants for V(1) and V(2) sites. The data confirms the existence of only one spin component and the ground state corresponds to a non-magnetic spin singlet. The T dependence of Kiso above 120 K follows the nature of cspin(T) proposed by Hatfield for alternating chain model. Below 80 K, it follows the expression for cspin of a one-dimensional chain with a spin-gap D which corresponds to about 215 - 3 K. The 51V spin-lattice relaxation rate, identical in both V sites, follows an Arrhenius type of temperature dependence in between 300-40 K, yielding a gap of D = 380 K, which is larger than that obtained from shift data.
3. NMR study on the evolution of ball-milled Al-Cu-Nb alloy
Aluminum based intermetallic alloys with high specific strength have applications in aviation and transport industry. Recently, a number of Al-Cu-Nb composites have been prepared through mechanical alloying in a planetary ball mill and characterized by different techniques. In this report, the technique of NMR has been used to monitor the changes in the atomic environment of the probed nucleus as a result of milling. 27A1, 63Cu, 65Cu and 93Nb NMR at different stages reveal alloy formation and partial solid state amorphization, followed/ accompanied by strain induced nucleation of nanocrystalline intermetallic phases.