Showing papers by "K. Mukherjee published in 2018"

Complex magnetic behaviour and evidence of a superspin glass state in the binary intermetallic compound Er5Pd2.

Abstract: The binary intermetallic compound Er5Pd2 has been investigated using dc and ac magnetic susceptibilities, magnetic memory effect, isothermal magnetization, non-linear dc susceptibility, heat capacity and magnetocaloric effect studies. Interestingly, even though the compound does not show geometrical frustration it undergoes glassy magnetic phase transition below 17.2 K. Investigation of dc magnetization and heat capacity data divulged absence of long-ranged magnetic ordering. Through the magnetic memory effect, time dependent magnetization and ac susceptibility studies it was revealed that the compound undergoes glass-like freezing below 17.2 K. Analysis of frequency dependence of this transition temperature through scaling and Arrhenius law; along with the Mydosh parameter indicate, that the dynamics in Er5Pd2 are due to the presence of strongly interacting superspins rather than individual spins. This phase transition was further investigated by non-linear dc susceptibility and was characterized by static critical exponents γ and δ. Our results indicate that this compound shows the signature of superspin glass at low temperature. Additionally, both conventional and inverse magnetocaloric effect was observed with a large value of magnetic entropy change and relative cooling power. Our results suggest that Er5Pd2 can be classified as a superspin glass system with large magnetocaloric effect.

Nature of glassy magnetic state in magnetocaloric materials Dy5Pd2-xNix (x = 0 and 1) and universal scaling analysis of R5Pd2 (R = Tb, Dy and Er)

Abstract: We report a systematic investigation of the magnetic and magnetocaloric properties of Dy5Pd2 and Dy5PdNi. Our study on these compounds gave evidence that they exhibit complex magnetic behaviour along with the presence of glass-like magnetic phase. Furthermore, in these compounds both second order and first order phase transitions were present, which were validated through Arrott plots and Landau parameter analysis. AC susceptibility along with time dependent magnetisation study has confirmed the presence of double cluster glass-like freezing in both Dy5Pd2 and Dy5PdNi. These compounds show significant value of isothermal entropy change and relative cooling power and these values increased with Ni substitution. Beside conventional magnetocaloric effect, inverse magnetocaloric effect was noted in these compounds, which might arise due to the presence of complex non-equilibrium magnetic state. Along with these compounds a universal characteristic curve involving two other members of R5Pd2 family i.e. Er5Pd2 and Tb5Pd2 was constructed. The master curve reaffirmed the presence of both second and first order magnetic phase transition in such compounds which were in analogy to our results of Arrott plots and Landau parameter analysis. Additionally, magnetic entropy change followed the power law and the obtained exponent values indicated the presence of mixed magnetic interactions in these compounds.

Effect of (Cu/Fe)O5 bipyramid size and separation on magnetic and dielectric properties of rare earth layered perovskite LaBaCuFeO5 and LuBaCuFeO5

Abstract: We report structural, magnetic and dielectric properties of layered perovskite materials LnBaCuFeO5 (Ln = La and Lu). LaBaCuFeO5 shows magnetic cluster glass behavior below 60 K owing to the competing ferromagnetic and antiferromagnetic exchange interactions. Glassy dynamics of electric dipoles has also been observed in the vicinity of the magnetic glass transition temperature. The presence of significant coupling between spin and polar degrees of freedom results in the multiglass feature in LaBaCuFeO5. The LuBaCuFeO5 compound undergoes YBaCuFeO5 like commensurate to incommensurate antiferromagnetic transition at 175 K. Large magnetic irreversibility below 17 K in this compound suggests the presence of strong spin anisotropy. In addition, in this compound the interaction between the dipoles is not strong enough, which results in the absence of glassy dynamics of electric dipoles. The contrasting behavior of two compounds is possibly due to variation in the ferromagnetic and antiferromagnetic interactions along c-axis, which is the manifestation of structural modification arising out of the difference in the ionic radii of La and Lu.

Evidence of partial gap opening and Ce-site dilution effects in a heavy fermion compound CeNiGe2

Abstract: We report the results of magnetization, non-linear dc susceptibility, electrical transport, and heat capacity measurements on Y-substituted heavy fermion CeNiGe2. Investigations are carried out on the compounds CeNiGe2, Ce0.9Y0.1NiGe2, Ce0.8Y0.2NiGe2 and Ce0.6Y0.4NiGe2. It is observed that with the increase in Y-concentration, the magnetic ordering temperature decreases. For CeNiGe2, below ordering temperature Arrott plots suggest the presence of spin density wave (SDW). Third and fifth order dc susceptibility indicates magnetic instability which possibly leads to partial gap opening resulting in the observation of SDW. These observations are further investigated through resistivity and heat capacity measurements which also point toward partial gap opening in CeNiGe2. Interestingly, with the increase in Y-substitution, it is noted that the gap opening is suppressed and also shifted towards lower temperature. Moreover, our investigations reveal absence of non-Fermi liquid behavior or zero field quantum critical point even after 40% dilution of Ce-site.

Crystal structure and magnetism of layered perovskites compound EuBaCuFeO5

Abstract: Layered perovskite compounds have interesting multiferroic properties.YBaCuFeO5 is one of the layered perovskite compounds which have magnetic and dielectric transition above 200 K. The multiferroic properties can be tuned with the replacement of Y with some other rare earth ions. In this manuscript, structural and magnetic properties of layered perovskite compound EuBaCuFeO5 have been investigated. This compound crystallizes in the tetragonal structure with P4mm space group and is iso-structural with YBaCuFeO5. The magnetic transition has been found to shift to 120 K as compared to YBaCuFeO5 which has the transition at 200 K. This shift in the magnetic transition has been ascribed to the decrease in the chemical pressure that relaxes the magnetic moments.Layered perovskite compounds have interesting multiferroic properties.YBaCuFeO5 is one of the layered perovskite compounds which have magnetic and dielectric transition above 200 K. The multiferroic properties can be tuned with the replacement of Y with some other rare earth ions. In this manuscript, structural and magnetic properties of layered perovskite compound EuBaCuFeO5 have been investigated. This compound crystallizes in the tetragonal structure with P4mm space group and is iso-structural with YBaCuFeO5. The magnetic transition has been found to shift to 120 K as compared to YBaCuFeO5 which has the transition at 200 K. This shift in the magnetic transition has been ascribed to the decrease in the chemical pressure that relaxes the magnetic moments.