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In this study, the structural properties of La0.7Sr0.3MnO3 (LSMO) manganite synthesized in bulk and nano form have been analyzed in detail. The bulk LSMO was synthesized by the solid-state method whereas the LSMO nanoparticles was prepared using the sol-gel route. The structural properties of the prepared samples were examined using X-Ray diffraction (XRD). Rietveld refinement confirmed that all the samples crystallize in R-3c space group with a rhombohedral structure. Williamson-Hall (WH) Analysis using Uniform deformation model and Size strain plots (SSP) were employed to determine the average crystallite size and microstrain in the synthesized samples. SEM and TEM measurements have also been taken to analyse their size distribution.

Materials with a large magnetocaloric effect are of great significance for applications in thermomagnetic power generation and magnetic refrigeration. We report the effect of cobalt addition on the structural, magnetic, and magnetocaloric properties of Gd5 Si1.7 Ge2.3− x Co x with $x = 0$ , 0.1, 0.2, 0.3, and 0.4. Rietveld refinement of the X-ray diffraction patterns reveals that the Gd5 Si1.7 Ge2.3− x Co x compounds with $x\le 0.3$ crystallize in a mixed state of monoclinic and orthorhombic structures. With the increase in Co concentration, the compounds stabilize in orthorhombic structure with the Pbnm space group. Magnetization measurements indicate first-order and second-order transitions for lower Co concentrations ( $x\le 0.3$ ), while for the composition with $x=0.4$ , only a second-order transition is evident, which is due to the stabilization of the orthorhombic structure for higher compositions. At lower fields, short-range ferromagnetic correlations are apparent, which is attributed to the presence of competing intra-layer and inter-layer magnetic interactions. An enhancement in Curie temperature has been observed from 243 to 283 K with an entropy change ( $-\Delta S_{M}$ ) of 12.8 at 243 K, 14.5 at 262 K, 10.4 at 270 K, and 5.8 J/kg $\cdot \text{K}$ at 283 K for $x = 0.1$ , 0.2, 0.3, and 0.4, respectively, for a field change of 5 T. Universal curve analysis corroborates the transition of first order to second order as evidenced by magnetization measurements. The ability to tune the transition temperature to near room temperature through the proper addition of transition elements could provide an interesting pathway toward the development of materials for room temperature refrigeration applications.

In the present work, polycrystalline Ni50Mn36Sn14-xInx (x = 0, 1, 2 and 3) Heusler alloys were prepared. The influence of In substitution for Sn on the crystal structure, martensitic transition (MT) and magnetic properties have been investigated for these alloys. Structural analysis indicate that the samples possess L21 structure at room temperature. With increasing In content, the martensitic transition shifts to a higher temperature, while the Curie temperature of austenite phase moves to a lower temperature. The maximum entropy change ( Δ SM) max near the martensitic transition is found to be 8.4 J/kgK, 9.8 J/kgK, 10.1 J/kgK and 19.2 J/kgK for x = 0, 1, 2 and 3 respectively, for a field change of 50 kOe. The entropy change around the Curie temperature of the austenite phase is found to be – 2.9 J/kgK, −1.8 J/kgK, −4.1 J/kgK and −3.9 J/kgK respectively for x = 0, 1, 2 and 3 alloys, for a field change of 50 kOe. The effective RCP values are 80 J/kg, 15.6 J/kg, 65.8 J/kg and 69.4 J/kg for x = 0, 1, 2 and 3 alloys respectively, near the first order transition region. The RCP values are higher around the second order transition region due to the broad nature of Δ SM curves. The corresponding values are 114 J/kg, 92 J/kg, 121 J/kg and 132 J/kg for x = 0, 1, 2 and 3 alloys, respectively. Moreover, the critical behavior of Ni50Mn36Sn14-xInx (x = 1, 2 and 3) Heusler alloys around the ferromagnetic-paramagnetic transition region of austenite phase is studied from the field dependence of magnetic entropy change. The critical exponent values are close to the theoretical prediction of mean field model with a slight deviation.

We report on the observation of double transition - a first order and a second order transition in Gd5Si2-xCoxGe2 with x = 0, 0.1, 0.2 and 0.4 with the appearance of short-range ferromagnetic correlations. The first order phase transition is due to a combined magnetostructural transition from monoclinic paramagnetic phase to orthorhombic ferromagnetic phase on cooling while the second order transition arises from an orthorhombic paramagnetic to ferromagnetic phase on cooling. Structural studies show that the substituted compounds crystallize in a combination of Gd5Si2Ge2 and Gd5Si4 phases. Low-temperature X-ray diffraction measurements confirm the complete transformation from monoclinic to orthorhombic phase. DC magnetization measurements reveal an anomalous low field magnetic behaviour indicating a Griffiths-like phase. This unusual behaviour is attributed to the local disorder within the crystallographic structure indicating the presence of short-range magnetic correlations and ferromagnetic clustering, which is stabilized and enhanced by competing intra-layer and inter-layer magnetic interactions. The magnetostructural transition results in entropy changes -Delta S-M) of 9J kg(-1) K-1 at 260 K for x=0.1,8.5 Jkg(-1) K-1 at 245 K for x=0.2 and 4.2J kg(-1) K-1 at 210 K for x = 0.4 for a field change of 50 kOe. Co substitution induces compelling crystallographic and magnetoresponsive effects in the Gd-Si-Ge system, which could be useful for potential and smart applications such assolid-state magnetic refrigeration and sensitive magnetic switching from paramagnetic to ferromagnetic state. Universal curve analysis has been carried out on the substituted samples to study the order of the magnetic transition.

The martensitic transition and exchange bias properties of the Heusler alloy system Ni50Mn36Sn14-xSix (x = 0, 1, 2 and 3) have been investigated. As the Si concentration increases, the martensitic transition temperature decreases while the Curie temperature of the austenite phases shows a slight increase. The temperature dependence of AC susceptibility with different frequencies at a low temperature regime was analyzed and the frequency dependence of the spin freezing temperature (T-f) showing a conventional critical slowing down relation confirms the spin glass behavior at low temperatures. Furthermore, the sample was recognized as a reentrant spin glass with both ferromagnetic and glassy states coexisting at least in the field cooled state. Due to these competing magnetic interactions, all the studied alloys exhibit exchange bias at low temperatures. For x = 2 alloy, an exchange bias field of 235 Oe is observed. However, on further increasing x, the exchange bias decreases. Therefore, it is quite evident that the unidirectional anisotropy decreases as a function of Si concentration. The double shifted hysteresis loop after zero field cooling and training effect strongly support the presence of exchange bias in these alloys. The dependencies of EB on various parameters like temperature and cooling field have also been investigated.

In the present work, Nd substituted Gd5-xNdxSi2Ge2 with x = 0.05, 0.1 and 0.2 have been synthesized by arc melting and the effect of Nd substitution on the structural and magnetocaloric properties of Gd5Si2Ge2 has been investigated. The composition with x=0.05 undergoes a first order phase transition with a Curie temperature of 275 K. With the increase in Nd content to x=0.1 and x=0.2, the compounds undergo a second order magnetic transition at 300 K and 293 K respectively. Maximum entropy changes (-ΔSM) for Gd5-xNdxSi2Ge2 alloys with x = 0.05, 0.1 and 0.2 are 12.8, 7.6 and 7.2 J/kg K, respectively, for 50 kOe. The critical exponent analysis of the paramagnetic to ferromagnetic transition and the scaling behaviour of field dependence of MCE for x=0.1 and 0.2 compositions is also carried out.

We report on the observation of double transition - a first order and a second order transition in Gd

In the present investigation, the effect of iron addition on the structural, magnetic and magnetocaloric properties of Gd5Si1.7Ge2.3-xFex alloys with x = 0–0.4 has been carried out. Structural analysis reveal that Gd5Si1.7Ge2.3-xFex compounds crystallize in a combination of monoclinic and orthorhombic structures at room temperature. With increase in Fe substitution up to x ≤ 0.3, the compounds stabilize in orthorhombic structure with Pbnm space group. First-order and second-order transitions are observed for low Fe concentrations. For x = 0.4, only a second-order transition is evident which is due to the stabilization of the orthorhombic structure. At lower fields, the presence of short-range ferromagnetic correlations indicate competing intra-layer and inter-layer magnetic interactions. The Curie temperature increases from 243 K to 287 K with increase in Fe concentration. The entropy change (-ΔSM) is found to be 10.1 J/kg K at 247 K, 11.3 J/kg K at 253 K, 7.9 J/kg K at 273 K and 7 J/kg K at 287 K for x = 0.1, 0.2, 0.3 and 0.4 respectively, for a field change of 50 kOe. Universal curve analysis corroborates the transition from first-order to second-order as evidenced by magnetization measurements. Tuning the transition temperature to near room temperature through the proper substitution of transition elements paves an interesting route towards the development of materials for room temperature refrigeration applications.

The effect of Ge substitution on the magnetic, magnetocaloric, and exchange bias properties of Heusler alloy system Ni50Mn36Sn14-xGex (x = 1, 2) has been investigated. With the increase of Ge content, the cell volume decreases due to the smaller Ge radius and the martensitic transition temperature increases, while the Curie temperature of the austenite phase shows a small decrease. Metamagnetic behavior is observed in the low temperature magnetization isotherms for x = 1, whereas it is less pronounced in x = 2. The maximum magnetic entropy changes associated with the martensitic transition are 7.8 J/kg K and 2.3 J/kg K for x = 1 and 2, respectively, for a field change of 5 T. Relative cooling power is found to be more in the vicinity of the Curie temperature of the austenite phase, compared to that at the martensitic transition temperature in both x = 1 and 2. At low temperatures, both the samples exhibit exchange bias effect, with x = 2 showing higher value of exchange bias field. This is ascribed to the coexistence of ferromagnetic and antiferromagnetic interactions in these alloys. Further, the critical behavior of the austenite phase of both the alloys is studied and the values of the critical exponents are found to be different from the mean field values, which is attributed to the magnetic inhomogeneity originated due to Ge substitution. (C) 2015 AIP Publishing LLC.

The effect of cobalt doping on the structural, magnetic and magnetocaloric properties of electron-doped manganite La0.7Te0.3Mn1-xCoxO3 (x = 0, 0.1, 0.2, 0.25, 0.3 and 0.5) has been investigated. The parent compound La0.7Te0.3MnO3 crystallizes in a rhombohedral structure with R (3) over barc space group. With the increase in Co concentration to x = 0.2, a structural transition from rhombohedral (R (3) over barc space group) to orthorhombic (Pbnm space group) is observed. X-ray photoelectron spectroscopy (XPS) indicates that the structural transition is due to the disordered distribution of Mn2+/Mn3+ and Co2+/Co3+ ions. All the samples undergo a paramagnetic-ferromagnetic (PM-FM) phase transition. With the increase in Co content to x = 0.1, the unit cell volume increases with a decrease in both Mn-O-Mn bond angle and T-c indicating a weakening of the double exchange interaction. However, with further increase in Co concentration, T-c increases. The presence of competing ferromagnetic and antiferromagnetic interactions leads to a glassy behaviour at low temperatures for low Co doping concentrations. However, for higher Co concentrations, no such behaviour is observed. Arrott plots reveal a second order nature of magnetic transition for all the samples. The magnetic exchange interactions for x = 0.3 and 0.5 follow the mean-field model. Magnetization results show that the magnetocaloric property of the electron-doped manganite is affected by the substitution of Co at Mn sites. Relatively large values of relative cooling power and broad temperature interval of the magnetocaloric effect make the present compounds promising for sub-room temperature magnetic refrigeration applications.

Structural and magnetocaloric properties of Nd substituted Gd5-xNdxSi2Ge2 with x = 0.05, 0.1, and 0.2 have been investigated. The composition with x = 0.05 crystallizes in monoclinic Gd5Si2Ge2 structure with P112(1)/a space group and undergoes a first order phase transition with a Curie temperature of 275 K. With increase in Nd content to x = 0.1, the compound is found to stabilize in orthorhombic Gd5Si4 phase with Pnma space group. The compounds with x = 0.1 and 0.2 undergoes a second order magnetic transition at 300K and 293 K, respectively. Temperature variation of maximum entropy change for Gd5-xNdxSi2Ge2 alloys with x = 0.05, 0.1, and 0.2 are 7.9, 3.7, and 3.2 J/kg K, respectively, for a field change of 20 kOe, and 12.8, 7.6, and 7.2 J/kg K, respectively, for 50 kOe. A large relative cooling power of 295, 205, and 188 J/kg are obtained for x = 0.05, 0.1, and 0.2, respectively, fulfilling the required criteria for a potential magnetic refrigerant in the room temperature regime. (C) 2015 AIP Publishing LLC.