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Magnetic cooling requires energy-efficient and eco-friendly alternatives to conventional rare earth element-based materials, which rely on materials with customized magnetic and structural properties. This study introduces the growth of iron oxide thin films for designing magnetocaloric materials, using a phenomenological model to screen candidates for the magnetocaloric effect (MCE) and inverse magnetocaloric effect (IMCE). Based on the Curie temperature (TC) window concept, ferrimagnetic Fe3O4 and the antiferromagnetic α-Fe2O3 and FeO thin films are identified as potential candidates for structural transitions (TV) and spin rearrangement (TN) achieved by manipulating their nanoscale ordering temperatures. These oxide films exhibit IMCE with a maximum entropy change (ΔSmax) ranging from 0.13 to 1.87 J/kg-K at TV and/or TN, while demonstrating the MCE effect at low temperatures. Interestingly, we demonstrate that IMCE can occur in Fe3O4 thin films without a structural transition but with a change in anisotropy. In addition, utilizing textured growth to tailor magneto-structural coupling in thin films is predicted as a novel approach for engineering magnetocaloric materials. [ABSTRACT FROM AUTHOR]

Understanding the effects of interparticle interactions is a vital problem because magnetic nanoparticles showcase a variety of magnetic configurations due to different contributions to their total energy. To derive reliable and robust properties from magnetic nanoparticles, it is, thus, necessary to understand the competition between particle anisotropy and interparticle interactions that define the magnetic state of nanoparticles, where size control plays an important role. Here, we apply the random anisotropy model (RAM) that considers various magnetic interactions to selectively prepared NiCr nanostructures (NiCr dense nanoclusters, nanogranular NiCr thin films, and Ag(NiCr) nanocomposites) with different interparticle interactions. The estimated single-particle magnetic anisotropy K values (2.82 − 12.3 × 104 J/m3) and careful analysis of magnetization behavior for these nanostructures reveal that orbital hybridization, surface segregation, and interface character govern the magnetic interactions among nanoparticles. Our study demonstrates how magnetic behaviors vary in these different magnetic systems consisting of superparamagnetic (SPM) and ferromagnetic (FM) contributions specific to magnetic interactions. [ABSTRACT FROM AUTHOR]

From multicomponent high-entropy alloys (AlCoCrFeNi) through ternary alloys (CrFeNi) to binary (NiCr) alloys, Cr doping plays a critical role in altering the magnetocaloric properties of the resultant alloys. Magnetocaloric effect (MCE) of Ni100−xCrx (x = 5, 10, 15 at.%) nanogranular thin films were investigated by varying Cr concentration, which demonstrate near room-temperature magnetic entropy change (− ΔSM = 0.08 J/kg K) and relative cooling power (RCP = 25 J/kg) at 10 at.% Cr. The MCE properties are well predicted using a phenomenological model based on magnetization as a function of temperature, and they correlate well with experimentally measured magnetic isotherms. [ABSTRACT FROM AUTHOR]

Zn-ferrite is a versatile material among spinels owing to its physicochemical properties, as demonstrated in rich phase diagrams, with several conductive or magnetic behaviors dictated by its cation inversion. The strength and the type of cation inversion can be manipulated through the various thermal treatment conditions. In this study, inverted Zn-ferrite thin films prepared from radio frequency magnetron sputtering were subjected to different in situ (in vacuum) and ex situ (in air) annealing treatments. The temperature and field dependence of magnetization behaviors reveal multiple magnetic interactions compared to its bulk antiferromagnet behavior. Using the magnetic component model, the different magnetic interactions can be explained in terms of superparamagnetic (SPM), paramagnetic (PM), and ferrimagnetic (FM) contributions. At low temperatures, the SPM and FM contributions can be approximated to the hard and soft ferrimagnetic phases of Zn-ferrite, respectively, which changes with the annealing temperature and sputter power. Distinct magnetic properties emanating from in situ annealing compared to the ex situ annealing were ascribed to the nonzero Fe2+/Fe3+ ratio, leading to the different magnetic interactions. The anisotropy was found to be the key parameter that governs the behavior of annealed in situ samples. [ABSTRACT FROM AUTHOR]

• Optimized growth of polycrystalline VO 2 films on SiO 2 /Si substrates by Sputtering. • Appreciable insulator to metal transition (IMT) observed down to 23 nm film thickness. • Film thickness induce systematic modulation in IMT order and IMT temperature. • Low resistivity (∼10−2 Ω-cm) achieved for insulator state in 23 and 38 nm films. Engineering electronic properties of VO 2 across its insulator to metal transition enable to design wide range of electronic devices operating with low voltage such as memristor, field effect transistor, and in neuromorphic device as an active circuit element. We investigated the electrical and structural properties of sputter deposited VO 2 thin films grown on SiO 2 /Si substrates. In polycrystalline VO 2 films, we observed appreciable insulator to metal transition (IMT) down to film thickness of 23 nm. Further, thickness dependence study reveals a systematic variation in the IMT order between 30-3000, accompanied by modulation in transition temperature and hysteresis. The genesis of the modulations is attributed to morphological and structural growth dynamics. Significantly, we have attained low values for insulating states (∼10−2 Ω-cm) in low dimensional thin films (23 and 38 nm), which are desirable for Joule heating driven IMT based VO 2 devices with low voltage switching, as well as for sensing applications. [ABSTRACT FROM AUTHOR]

• Fabrication of SrFe 12 O 19 /α-Fe 2 O 3 or SrFe 12 O 19 /γ-Fe 2 O 3 nanocomposite thin films. • Substantial coercivities (∼5.8 kOe) achieved without high-temperature processing. • Strain-induced shifting of the Morin transition of α-Fe 2 O 3. • Simultaneous hard and soft magnetic properties observed at room temperature. Ferromagnetic (FM)/antiferromagnetic (AFM) or hard-FM/soft-FM nanocomposites are compelling due to their benefits in future spintronics. We fabricated two distinct nanocomposites thin films by altering the gaseous environment during laser ablation of SrFe 12 O 19 : one in a vacuum (FM/AFM: SrFe 12 O 19 /α-Fe 2 O 3) and other in an oxygen atmosphere (hard-FM/soft-FM: SrFe 12 O 19 /γ-Fe 2 O 3). The in-situ growth and ex-situ annealing temperatures significantly affect the composition of AFM, soft-FM, and hard-FM phases in nanocomposite films. M−H loops show substantial coercivity values (∼5 kOe) in room temperature grown FM/AFM nanocomposites films, while hard-FM/soft-FM nanocomposites films display an exchange spring system with hard (5.8 kOe) and soft (0.16 kOe) magnetic phases. Morin transition of AFM α-Fe 2 O 3 phase is shifted to a lower temperature of around 60 K compared to the bulk value of 260 K, owing to intergranular strain effect, and this has a detrimental effect on FM properties of FM/AFM nanocomposite films. Despite most research focuses on multilayers, the aforementioned unique magnetic properties in FM/AFM and hard-FM/soft-FM nanocomposites thin films hold significant relevance for numerous applications. [ABSTRACT FROM AUTHOR]