Tailoring of magnetocaloric response in nanostructured materials: Role of anisotropy

Abstract

The magnetocaloric response of an ensemble of oriented uniaxial magnetic objects, perpendicularly magnetized to their easy axes, for temperatures close to the blocking temperature is calculated with the aim of demonstrating that the control of the sample's microstructure makes up an effective way to tailor its magnetocaloric response. Coexisting positive and negative magnetocaloric effect ͑MCE͒ is found for a model material with a single magnetic phase transition. Both MCE regimes are controlled by the magnitude of the applied magnetic field. As a proof of concept, experimental results for arrays of self-assembled ferromagnetic nanowires embedded into highly ordered nanoporous anodic alumina templates are shown, suggesting the validity of the numerical calculations.

Excellent magnetocaloric properties of melt-extracted Gd-based amorphous microwires

“…[20][21][22] The use of these wires with increased surface areas will not only enhance heat transfer processes but also promote chemical reactions of solid refrigerant with liquid coolant used to transfer heat inside the system. 19 However, the MCEs achieved in the existing micro/nanowires [20][21][22] were relatively small (e.g., ÀDS M $ 0.7 J/kg K at 3 T for Ni 50.95 Mn 25.45 Ga 23.6 microwires 22 ), making them unsuitable for AMR applications. In this letter, the excellent magnetocaloric properties of Gd-based amorphous microwires, which were fabricated by a modified precision melt-extraction method, are reported.…”

“…21 Therefore, in the present work, we have performed a comparative study of the magnetic and magnetocaloric properties of the wire-shaped sample (the average length is 5 mm) and the bulk rectangular-shaped sample (the length, width, and thickness are 2.5 mm, 1.78 mm, and 0.76 mm, respectively). While the magnetic field was applied along the microwires during magnetic measurements, it was applied in-plane and out-ofplane to the rectangular-shaped sample.…”

Field dependence of the magnetocaloric effect in core-shell nanoparticles

“…11,12 More recently, it has been shown that the adequate control of the magnetic anisotropy of a nanostructured system can originate behaviors that are qualitatively different from those of the bulk materials. 13 There have been studies of the influence on the MCE of the control of the anisotropy of the material, especially through surface modification processes, either by ball-milling zinc ferrite particles, 14 which lead to disorder on the surface of the particles causing some of the ions to change from spinel to the inverse spinel structure, or by systems of core-shell nanoparticles, 15 where the total magnetization of each particle may be considered as consisting of two parts: the core magnetic moment ͑which is ordered and behaves as a superspin͒ and the shell magnetization ͑which is mostly disordered and somewhat similar to spin-glass systems͒. The exchange coupling between the surface and core spins can lead to short-range order of the surface spins below a certain temperature with the surface anisotropy also competing in this process.…”

Superparamagnetism and Monte Carlo Simulations

“…They resemble one-dimensional columnar parallel chains of magnetic nanoparticles under different spatial arrangement (square, hexagonal) and different lengths along the X-axis. The study of such type of structures is at the center of much research nowadays for the basic study of the competition between the enhanced anisotropy and magnetostatic interactions [31][32][33][34][35]. The magnetic properties of such chain-like systems exhibit a good analogy to the behavior of ferromagnetic nanowires [36].…”