The aim of the present paper was to study the large magnetocaloric effect observed in LaFe _11.35 Co _0.6 Si _1.05 alloy. X‐ray diffraction (XRD) result reveals a coexistence of two crystalline phases: a dominant La(Fe,Si) ₁₃ ‐type and a minor α‐Fe(Co,Si). It is confirmed by the Mössbauer spectroscopy and microstructural observations accompanied by an energy‐dispersive spectroscopy (EDS) analysis. The value of the magnetic entropy changes (| S _M |) in the vicinity of the Curie temperature ( T _C = 268 K) was calculated using thermomagnetic Maxwell relation, and it equals to 21.4 J·kg ⁻¹ ·K ⁻¹ under the change in an external magnetic field of μ ₀ Δ H = 3T. The investigation of magnetic phase transition was carried out using the Landau theory, an analysis of the field dependences of the magnetic entropy change and universal scaling curve, revealing the second order of phase transition in the studied material.

The spontaneous oxidation of a magnetite surface and shape design are major aspects of synthesizing various nanostructures with unique magnetic and electrical properties, catalytic activity, and biocompatibility. In this article, the roles of different organic modifiers on the shape and formation of an oxidized layer composed of maghemite were discussed and described in the context of magnetic and electrical properties. It was confirmed that Fe₃O₄ nanoparticles synthesized in the presence of triphenylphosphine could be characterized by cuboidal shape, a relatively low average particle size (9.6 ± 2.0 nm), and high saturation magnetization equal to 55.2 emu/g. Furthermore, it has been confirmed that low-frequency conductivity and dielectric properties are related to surface disordering and oxidation. The electric energy storage possibility increased for nanoparticles with a disordered and oxidized surface, whereas the dielectric losses in these particles were strongly related to their size. The cuboidal magnetite nanoparticles synthesized in the presence of triphenylphosphine had an ultrahigh electrical conductivity (1.02 × 10⁻⁴ S/cm at 10 Hz) in comparison to the spherical ones. At higher temperatures, the maghemite content altered the behavior of electrons. The electrical conductivity can be described by correlated barrier hopping or overlapping large polaron tunneling. Interestingly, the activation energies of electrons transport by the surface were similar for all the analyzed nanoparticles in low- and high-temperature ranges.

The aim of the paper is to present a study of the magnetocaloric effect and the nature of phase transition in the Gd₈₀Ge₁₅Si₅ (S1), Gd₇₅Ge₁₅Si₅Ni₅ (S2), Gd₇₅Ge₁₅Si₅Pr₅ (S3) and Gd₇₅Ge₁₅Si₅Nd₅ (S4) alloys. The magnetic entropy changes determined for studied samples, under external magnetic field ~3T, were 11.91, 12.11, 5.08 and 4.71 J/(kg K) for S1, S2, S3 and S4, respectively. The values of refrigerant capacity (under ~3T) were 164, 140, 160 and 140 J/kg for S1, S2, S3 and S4, respectively. The first order phase transition was detected for samples S1 and S2, while specimens S3 and S4 manifested the second order phase transition at the Curie point (T_C). The analysis of temperature evolution of the exponent n (ΔS_M = C·(B_max)ⁿ) showed the validity of this method in detecting either the first or the second order phase transition and the structural transition. The analysis of critical behavior was carried out for samples S3 and S4. The critical exponents and precise T_C values were calculated. The ascertained critical exponents were used to determine the theoretical value of the exponent n, which corresponded well with experimental result.