Observation of Griffiths Phase, Critical Exponent Analysis and High Magnetocaloric Effect Near Room Temperature at Low Magnetic Field in V doped La0.7Sr0.3MnO3

We report on observation of Griffiths phase, high magnetocaloric properties at low magnetic fields and temperature dependent critical exponents of La0.7Sr0.3VxMn1-xO3 (x=0, 0.05 & 0.1) perovskite bulk materials. The Curie temperature (TC) of pure La0.7Sr0.3MnO3 is seen to be 368.7 K and decreases towards room temperature (342.2 K) by 10 mol% vanadium doping at the Mn site. Vanadium doping leads to enhancement in magnetic entropy change (-SM) from 1 Jkg-1K-1to 1.41 Jkg-1K-1. Vanadium doping at Mn site leads to the formation of Griffiths phase, a magnetic disorder due to the co-existence of paramagnetic matrix and short range ferromagnetic clusters. X-ray photoelectron spectroscopy analysis confirm the presence of mixed valance V4+/V5+along with Mn3+/ Mn4+ ions contributing to various double exchange interactions. Nature of phase transitions and magnetic interactions are analyzed by evaluating critical exponents and. All the samples show second-order ferromagnetic (FM) to paramagnetic (PM) phase transition, confirmed from the modified Arrott’s plots and critical exponent analysis carried out using Kouvel-Fisher method. Enhancement in magnetic entropy change along with the decrease in Curie temperature towards room temperature by vanadium doping in the La0.7Sr0.3MnO3 oxides indicates the possible application of these materials for the magnetic refrigeration at low magnetic fields.

Microstructure and Magnetocaloric Effect by Doping C in La-Fe-Si Ribbons

The melt-spun ribbons of LaFe11.5Si1.5Cx (x = 0, 0.1, 0.2, 0.3) compounds are prepared by the melt fast-quenching method. The doping of C is beneficial to the nucleation and precipitation of the La (Fe, Si)13 phase, which is indicated by the microstructure observation and the elemental analysis. Subsequently, the ribbons of LaFe11.5Si1.5C0.2 are annealed at different times, and the phase composition, the microstructures, and the magnetic properties are investigated. The LaFe11.5Si1.5C0.2 ribbons annealed at 1273 K for 2 h achieved the best magnetic properties, and the maximum isothermal magnetic entropy change with a value of 9.45 J/(kg·K) upon an applied field of 1.5 T at an increased Curie temperature 255 K.

Magnetic and magnetocaloric effect in a stuffed honeycomb polycrystalline antiferromagnet GdInO3

The magnetic and magnetocaloric properties were studied in a stuffed honeycomb polycrystalline antiferromagnet GdInO3. The onset temperature of antiferromagnetic ordering was observed at ~ 2.1 K. Negligible thermal and magnetic hysteresis suggest a reversible magnetocaloric effect (MCE) in the GdInO3 compound. In the magnetic field changes of 0–50 kOe and 0–70 kOe, the maximum magnetic entropy change values are 9.65 J/kg K and 18.37 J/kg K, respectively, near the liquid helium temperature, with the corresponding relative cooling power values of 115.01 J/kg and 211.31 J/kg. The MCE investigation of the polycrystalline GdInO3 serves to illuminate more exotic properties in this frustrated stuffed honeycomb magnetic system.

Observation of a Broadened Magnetocaloric Effect in Partially Crystallized Gd60Co40 Amorphous Alloy

To investigate the effect of crystallization treatment on the structure and magnetocaloric effect of Gd60Co40 amorphous alloy, the melt-spun ribbons were annealed at 513 K isothermally for 20, 40 and 60 min. The results indicate that, with increasing annealing time, the Gd4Co3 (space group P63/m) and Gd12Co7 (space group P21/c) phases precipitated from the amorphous precursor in sequence. In particular, in the samples annealed for 40 and 60 min, three successive magnetic transitions corresponding to the phases of Gd4Co3, Gd12Co7 and remaining amorphous matrix were detected, which induced an overlapped broadened profile of magnetic entropy change (|ΔSM|) versus temperature. Under magnetic field changing from 0 to 5 T, |ΔSM| values of 6.65 ± 0.1 kg−1·K−1 and 6.44 ± 0.1 J kg−1·K−1 in the temperature spans of 180–196 K and 177–196 K were obtained in ribbons annealed for 40 and 60 min, respectively. Compared with the fully amorphous alloy, the enhanced relative cooling power and flattened magnetocaloric effect of partially crystallized composites making them more suitable for the Ericsson thermodynamic cycle.

Formability and Magnetic Properties of the Binary Nd-Co Amorphous Alloys

In this paper, binary Nd-Co alloys with compositional range from Nd72.5Co27.5 to Nd50Co50 were successfully vitrified into glassy state by a melt-spinning method. The glass formability of the metallic glasses (MGs) was studied and the best glass former in the binary Nd-Co alloys was obtained. Magnetic properties of the MGs were measured. The compositional dependence of Curie temperature of the MGs was observed. The mechanism for the spin-glass-like behaviors and high coercivity at low temperature, and their influence on the magnetic entropy change of the MGs, were investigated.

Icosahedron [Cl12]12- Templated Gigantic Gd158Co38 Nanocluster with the Largest Ln158 Core for Magnetic Cooling

The synthesis of large nano-sized cluster-molecules is a goal that synthesists and structural scientists have been pursuing, as well as a huge challenge. Herein, the largest 3d-4f metal clusters Cl12@Gd158Co38 and Br12@Gd158Co38 until now are obtained through the “multi-anions-template” strategy, with a protein-sized metal frame (ca. 4.3 × 3.6 × 3.5 nm3). Different from the mixed distribution of 3d and 4f metals and the hollow structure in the previous giant 3d-4f clusters, for the dense core-shell structure Cl12@Gd158Co38 and Br12@Gd158Co38, the Ln158 core with the highest Ln nuclearity number is induced by icosahedra-shaped templates [Cl12]12- or [Br12]12-, while 3d metals (Co) are distributed on its periphery. Their appearances point out a new structure type of non-open giant Ln-based clusters (metal number > 100) and provide an ideal model for studying the multi-level assembly of complex macromolecules. Additionally, Cl12@Gd158Co38 shows the largest magnetic entropy change (-∆Smmax = 46.95 J kg-1 K-1 under 2.0 K and ΔH = 7 T) among reported high-nuclearity 3d-4f clusters.