S.K. Giri

Surface spin glass and exchange bias effect in Sm0.5Ca0.5MnO3 manganites nano particles

In this letter, we report that the charge/orbital order state of bulk antiferromagnetic Sm0.5Ca0.5MnO3 is suppressed and confirms the appearance of weak ferromagnetism below 65 K followed by a low temperature spin glass like transition at 41 K in its nano metric counterpart. Exchange anisotropy effect has been observed in the nano manganites and can be tuned by the strength of the cooling magnetic field (Hcool). The values of exchange fields (HE), coercivity (HC), remanence asymmetry (ME) and magnetic coercivity (MC) are found to strongly depend on cooling magnetic field and temperature. HE increases with increasing Hcool but for larger Hcool, HE tends to decrease due to the growth of ferromagnetic cluster size. Magnetic training effect has also been observed and it has been analyzed thoroughly using spin relaxation model. A proposed phenomenological core-shell type model is attributed to an exchange coupling between the spin-glass like shell (surrounding) and antiferromagnetic core of Sm0.5Ca0.5MnO3 nano...

Giant spontaneous exchange bias effect in Sm1.5Ca0.5CoMnO6 perovskite

We report here on the enormously large value of the spontaneous exchange bias (SEB) of ~5.1 kOe in the Sm1.5Ca0.5CoMnO6 bulk double perovskite system after zero-field cooling from an unmagnetized state. Depending on the path used for measuring the magnetic hysteresis loop, P-type or N-type, the EB field varies significantly. Dc and ac magnetization reveals a super-spin-glass-like (SSG) state below 19 K. The EB effect has been observed below the glassy transition temperature. The conventional exchange bias (CEB) as well as the SEB increase with a decrease in temperature and show monotonic variation. All these interesting features can be explained through the multimagnetic phase of double perovskite and the onset of unidirectional anisotropy driven by interface exchange coupling between the SSG, turned isothermally into a field-induced superferromagnetic shell and antiferromagnetic core.

Large magnetocaloric effect and critical behavior in Sm0.09Ca0.91MnO3 electron-doped nanomanganite

The magnetic properties and magnetocaloric effect (MCE) in electron-doped Sm0.09Ca0.91MnO3 nanomanganite have been investigated in detail by magnetization and heat capacity measurements. The maximum magnetic entropy change and the relative cooling power (RCP) are found to be, respectively, and for a 7 T magnetic field change along with a negligible hysteresis loss, making of this material a promising candidate for magnetic refrigeration at low temperature. The maximum value of occurs close to the Curie temperature . The values of and RCP are comparable to a few hole-doped manganite. To investigate the nature of the paramagnetic-to-ferromagnetic phase transition, critical exponent study has been carried out. Based on the modified Arrott plot, we have determined the values of critical parameters ( and δ) and conclusively shown that Sm0.09Ca0.91MnO3 has nearly mean-field–like long-range interaction. The calculated values of critical exponents not only obey the scaling hypothesis, but also corroborate the results obtained employing the Kouvel-Fisher method. The re-scaled magnetic entropy change curves for different applied magnetic fields collapse into a single master curve for this electron-doped manganite indicating clearly a second-order magnetic phase transition. Such noticeably large at low magnetic field makes this material a potential candidate for low-temperature magnetic refrigeration.

Strain modulated large magnetocaloric effect in Sm0.55Sr0.45MnO3 epitaxial films

Epitaxial Sm0.55Sr0.45MnO3 thin films were deposited on LAO (001), LSAT (001), and STO (001) single crystalline substrates by pulsed laser deposition technique to investigate the correlation between the substrate induced film lattice strain and magnetocaloric effect (MCE). The film on LAO substrate (S_LAO), which is under compressive strain, undergoes ferromagnetic → paramagnetic transition at TC ∼ 165 K. The films on STO (S_STO) and LSAT (S_LSAT) substrates are under tensile strain and have TC ∼ 120 K and 130 K, respectively. At T < TC, the zero field cooled and field cooled magnetization curves of all the films show huge bifurcation. In case of S_STO and S_LSAT films, hysteresis is also observed between field cooled cooling and warming cycle in magnetization versus temperature measurement at low magnetic field similar to first order-like magnetic phase transition. No signature of first order magnetic phase transition has been observed in the case of S_LAO film. Most interestingly, both normal (i.e., neg...

Surface Spin Glass Ordering and Exchange Bias in Nanometric Sm0.09Ca0.91MnO3 Manganites

We have thoroughly investigated the entire magnetic state of under doped ferromagnetic insulating manganite Sm0.09Ca0.91MnO3 through temperature dependent linear and non‐linear ac magnetic susceptibility and magnetization measurements. This ferromagnetic insulating manganite is found to have frequency dependent ferromagnetic to paramagnetic transition temperature at around 108 K. Exchange‐ bias effect are observed in field ‐cooled magnetic hysteresis loops for this nanoparticle. We have attributed our observation to the formation of ferromagnetic cluster which are formed as a consequence of intrinsic phase separation below certain temperature in this under doped manganites. We have carried out electronic‐ and magneto‐transport measurements to support these observed results.

Exchange Bias Effect Concerned with Tunneling Magnetoresistance in

In this paper, we report the exchange bias (EB) effect along with tunneling magnetoresistance (MR) in polycrystalline Sm0.35Pr0.15Sr0.5MnO3 manganite. Analogous to the shift in the magnetic hysteresis loop along the field (H)-axis, a shift is also observed in the MR-H curve when the sample is cooled in a static dc magnetic field at 5 K. The values of exchange fields (HE), coercivity (HC), remanence asymmetry (ME) and magnetic coercivity (MC) are found to strongly depend on cooling magnetic field and temperature. Magnetic training effect (TE) is supportive experimental evidence which describes the decrease of exchange bias field when sample is successively field-cycled at a particular temperature. We have also observed TE in the shift of the MR-H curve which has been interpreted by the spin relaxation model. We have observed the time dependent resistivity below the spin freezing temperature. The unusual MR behavior is interpreted in terms of the intragranular interface effect between short-range ferromagnetic clusters and spin-glass matrix giving rise to the EB effect, which is of special interest for potential application in multifunctional spintronic devices.

{\hbox{Sm}}_{0.35} {\hbox{Pr}}_{0.15}{\hbox{Sr}}_{0.5}{\hbox{MnO}}_3

In this article, microstructural, magnetic, magneto-transport, electronic transport properties of Pr1-xSrxMnO3 system have been systematically studied in nanometric dimension over the range 0.2 ≤ x ≤ 0.4 by preparing the compound through pyrophoric reaction route. XRD diffraction measurements indicate that all the samples are in orthorhombic Pbnm space group. Electronic and magneto-transport properties of these materials have been thoroughly investigated in nanometric grain size modulation. These Sr doped compounds at x=0.3 exhibit more ferromagnetic metallic behavior at zero field and negative magneto resistance in low temperature. The different magnetic phase was found using ac magnetic susceptibility measurement. Magneto –transport nature is explained using spin polarization tunneling model.