Santanu Pakhira

Magnetic frustration induced large magnetocaloric effect in the absence of long range magnetic order

We have synthesized a new intermetallic compound Ho2Ni0.95Si2.95 in a single phase with a defect crystal structure. The magnetic ground state of this material found to be highly frustrated without any long range order or glassy feature as investigated through magnetic, heat capacity and neutron diffraction measurements. The interest in this material stems from the fact that despite the absence of true long range order, large magnetocaloric effect (isothermal magnetic entropy change, −ΔSM ~ 28.65 J/Kg K (~205.78 mJ/cm3 K), relative cooling power, RCP ~ 696 J/Kg (~5 J/cm3) and adiabatic temperature change, ΔTad ~ 9.32 K for a field change of 70 kOe) has been observed which is rather hard to find in nature.

Low-field induced large magnetocaloric effect in Tm2Ni0.93Si2.93: influence of short-range magnetic correlation

In this work, we report the successful synthesis of a new intermetallic compound Tm2 [Formula: see text] [Formula: see text] that forms in single phase only in defect crystal structure. The compound does not show any long range magnetic ordering down to 2 K. The material exhibits a large magnetic entropy change ([Formula: see text] J [Formula: see text] K-1) and adiabatic temperature change ([Formula: see text] K) at 2.2 K for a field change of 20 kOe which can be realized by permanent magnets, thus being very beneficial for application purpose. In the absence of long-range magnetic ordering down to 2 K, the metastable nature of low-temperature spin dynamics and short-range magnetic correlations are considered to be responsible for such a large magnetocaloric effect over a wide temperature region.

Role of the stability of charge ordering in exchange bias effect in doped manganites

In this work we have carried out an elaborate study on the magnetic properties and investigated the exchange bias phenomena of some charge-ordered (CO) manganites. The detailed study of Sm1−xCaxMnO3 (x = 0.5, 0.55, 0.6, 0.65, 0.7) compounds shows that Sm0.4Ca0.6MnO3, which is the most robust charge ordered material studied here, shows significantly large exchange bias field (HE) as compared to the other compounds. Our experimental results and analysis indicate that TCO, which reflects the stability of the charge-ordered state, is one of the key parameters for the exchange bias effect. Similar behaviour is found in other rare-earth analogues, viz., La1−xCaxMnO3 and Pr1−xCaxMnO3 compounds as well. We also found that with increasing stability of CO states in Sm1−xCaxMnO3 compounds, HE enhances due to increase in number and reduction in size of ferromagnetic clusters.

Magnetic properties of intermetallic compound Pr2NiSi3

We report here the synthesis and basic magnetic properties of a intermetallic compound Pr2NiSi3. The compound crystallizes in hexagonal AlB2 type crystal structure with space group P6/mmm. The compound orders antiferromagnetically below 2.6 K with a positive paramagnetic Curie temperature. Along with antiferromagnetic ordering experimental signature for presence of ferromagnetic interaction has also been observed for this compound.

Unusual bidirectional frequency dependence of dynamical susceptibility in hexagonal intermetallic Pr2Ni0.95Si2.95

In this study, the synthesis of a novel ternary intermetallic compound Pr2Ni0.95Si2.95 forming in single phase only by deliberately introducing vacancies in Ni/Si site is reported. The detailed studies on dc magnetization, heat capacity, ac magnetization & associated dynamical scaling, different types of non-equilibrium dynamical behaviour, viz., magnetic relaxation behaviour as a function of wait time and temperature, aging phenomena, and magnetic memory effect firmly establish that the compound exhibits spin freezing behaviour below 3.3 K (Tf). However, below Tf, temperature dependence of ac susceptibility data exhibit an additional peak that shows reverse frequency dependence to that generally observed in a glassy system. The unusual bidirectional frequency dependence in a single magnetic system is of significant interest and rarely reported in literature. Competing exchange interaction arising from c/a ~ 1 and crystallographic randomness driven magnetic phase separation has been argued to be responsible for such observation. The reverse frequency shift of the low temperature peak has been described on the basis of a simple phenomenological model proposed in this work.

Magnetic relaxation behaviour in Pr2NiSi3

Time dependent isothemal remanent magnetizatin (IRM) behaviour for polycrystalline compound Pr2NiSi3 have been studied below its characteristic temperature. The compound undergoes slow magnetic relaxation with time. Along with competing interaction, non-magnetic atom disorder plays an important role in formation of non-equilibrium glassy like ground state for this compound.