Search

Magnetic and magnetocaloric properties of a solid solution of MnNiSi and FeNiGe alloys with nominal composition Mn 0.53 Fe 0.47 NiSi 0.53 Ge 0.47 have been investigated through dc magnetic measurements in ambient as well as in high pressure conditions. The alloy undergoes magneto-structural transition from the paramagnetic hexagonal Ni 2 In type structure to the ferromagnetic orthorhombic TiNiSi-type structure on cooling around 160 K. The alloy shows significant amount of training effect in magnetization when it is thermally cycled through the first order martensitic transition. We observe a colossal magnetocaloric effect (MCE) ( Δ S = −70.1 J/kg-K for H = 0–50 kOe) in ambient condition around the magneto-structural transition ( ∼ 176 K). Application of external hydrostatic pressure results in a significant decrease in the MCE value of the alloy. Reasonably large value of refrigeration capacity (RC) in ambient as well as in high pressure conditions (RC = 184.4 and 123 J/kg in ambient and 5 kbar of external pressure respectively) confirms its acceptance as a good magnetic refrigerant for practical uses. Metamagnetic behavior of the alloy around the magneto-structural transition presumably plays the key role towards the observation of such colossal value of MCE. [ABSTRACT FROM AUTHOR]

The present study describes about the preparation of semisolid metal (SSM) slurry by using an oblique plate. In this process, A356 aluminum alloy melt partially solidifies while flowing over a bottom cooled oblique plate. Melt flow inertia shears columnar dendrites formed on plate wall into equiaxed/fragmented grains by resulting semisolid slurry at plate exit. Effects of plate length providing required shear and cooling rate enabling necessary solidification are investigated. A 3-phase numerical model vis-à-vis transport of mass, momentum, energy and species is developed for prediction of velocity, temperature, macrosegregation and solid fraction. Model uses volume of fluid (VOF) for tracking-metal-air-interface and finite volume method (FVM) with enthalpy based phase change algorithm for tracking-solid-liquid-interface within the metal. Darcy model is used for porous mushy zone. Slurry variable viscosity is represented by Oldenburg model. Stokes model incorporates solid phase movement and gravity effect along the flow. Dendrite fragmentation is considered for generation of moving solid phase. Solid movement is handled by coherency point and characteristic diameter of moving grains. Model neglects nucleation and growth kinetics, solidification shrinkage/expansion and thermo-solutal buoyancy. Slurry solid fractions at plate exit are 16%, 22%, and 27% for plate lengths of 200 mm, 250 mm, and 300 mm, respectively. And, are 5%, 22%, and 27% for heat transfer coefficients of 1000 W/m 2 -K, 2000 W/m 2 -K and 2500 W/m 2 -K, respectively. Numerical predictions agree well with experimental results. [ABSTRACT FROM AUTHOR]

A series of Ni-doped Ni 50+x Mn 35−x Sn 15 samples for x = −1, 0, 1, 2, 3 and 4 have been investigated by transport and dc magnetization measurements. The parent sample ( x = 0) undergoes martensitic phase transition around 180 K during cooling along with ferromagnetic Curie point ( T C ) to be 340 K. Interestingly, Ni doping at the Mn site leads to rather unusual non-monotonous variation of martensitic transition temperature ( T MS ) which is precisely corroborated by the similar non-monotonous variation of lattice volume ( V 300 K ). Between −1 ≤ x ≤ 2, the variation of various physical parameters in the studies alloys is conventional and can be explained on the basis of e / a ratio of the samples. However, for x > 2, parameters such as T C , T MS , V 300 K etc. show sudden change in the nature of their variation which is anomalous and cannot be accounted by the e / a ratio formalism. Present study reveals that possible reason behind this non-monotonous variation is closely connected with a self-sustained mechanism originating from the change in the strength of hybridization between Ni 3 d e g state and the excess Mn at the Sn site on Ni substitution. The samples also show large negative magnetoresistance near T MS with its magnitude showing similar non-monotonous variation with Ni doping. [ABSTRACT FROM AUTHOR]

Ground state magnetic properties of Eu 0.5 Sr 0.5 Mn 1− x Co x O 3 ( x = 0, 0.02, 0.05, and 0.1) with perovskite structure were investigated through dc magnetization and ac susceptibility measurements. Smaller ionic radii of Eu +3 ion makes the ground state magnetic properties of these compounds more interesting. The samples show magnetic memory, large relaxation, frequency-dependent ac susceptibility and aging effects at low temperature, which indicate glassy magnetic ground state in the studied samples. A gradual transition from the spin-glass like ground state to cluster-glass state is also observed with increasing Co concentration. This observation is due to the decrease in double exchange interaction between Mn 3+ and Mn 4+ ion and hence the ferromagnetic interaction with Co doping. [ABSTRACT FROM AUTHOR]

Highlights: [•] Eu0.5Sr0.5Mn1−x Co x O3 samples are found to be in Pbnm orthorhombic structure. [•] Ground state properties of studied samples are sensitive to Co concentration. [•] Except x =0.1, all other samples show field induced insulator-metal transition. [•] The samples show large (>99.9%) magnetoresistance below insulator-metal transition. [•] Low temperature resistivity depends strongly on previous history of applied field. [Copyright &y& Elsevier]

• Structural and magnetic properties of skyrmionic system, Cu 2 OSeO 3 are investigated. • Thermal hysteresis between FC and FCH data is observed. • Lattice distortion at the magnetic transition is noticed. • Large MCE is found near the ferrimagnetic transition for a small change in magnetic field. • The observed anomalous change in Cu(1)-Cu(2) distances tune the strength of the magnetic exchange interactions. [Display omitted] We report here the detailed investigation on structural and magnetic behavior of the polycrystalline sample of Cu 2 OSeO 3. The Mott insulator Cu 2 OSeO 3 is a fascinating material showing skyrmionic state and magneto-electric coupling. We observe clear signature of thermal hysteresis between field-cooled and field-cooled heating data in the low-field magnetization versus temperature curve just below the magnetic ordering temperature of T C ~ 60 K. Temperature dependent powder x-ray diffraction data indicate the presence of lattice anomaly below T C. The sample also shows reasonable value of conventional magnetocaloric effect for small value of applied magnetic field, which can be related to the change in the magnetic structure with field. [ABSTRACT FROM AUTHOR]

Systematic investigations on Ag-doped MnNiGe alloys of nominal compositions MnNi 1 − x Ag x Ge (x = 0.10, 0.15 and 0.20) have been performed through dc magnetic measurements in ambient as well as in high pressure conditions. All the Ag-doped alloys undergo martensitic type structural phase transition with a monotonic decrease in transition temperature with increasing Ag concentration. Room temperature x-ray powder diffraction data confirm the presence of both hexagonal and orthorhombic phase for 10% Ag-doped alloy whereas, 15% and 20% Ag-doped alloys are found to be purely hexagonal in nature. Gradual incorporation of ferromagnetic interaction with increasing Ag-concentration in otherwise antiferromagnetic alloy is clear from the magnetic investigations. Application of external hydrostatic pressure further favors ferromagnetism. In addition, these Ag-doped alloys also show a reasonably high magnetocaloric effect around the magnetic and structural transition temperatures which makes these alloys important for magnetic cooling applications. The robustness of the observed magnetocaloric properties have also been checked by high pressure measurements. • Non-magnetic Ag has been doped in the Mn site of MnNiGe alloy. • The studied alloys undergo first order magneto-structural transition. • Ag-doping induces ferromagnetism in otherwise antiferromagnetic alloys. • The sample shows a large magneto-caloric effect. • Effect of external hydrostatic pressure on the magnetic properties is studied. [ABSTRACT FROM AUTHOR]