Variation of the Curie Temperature in Porous Materials
- PDF / 296,466 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 97 Downloads / 160 Views
ion of the Curie Temperature in Porous Materials A. V. Shishulina*, V. B. Fedoseeva, and A. V. Shishulinab,c a
G.A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, Nizhny Novgorod, 603950 Russia b Dzerzhinsk Polytechnic Institute, Branch of R.E. Alekseev Nizhny Novgorod State Technical University, Dzerzhinsk, Nizhny Novgorod oblast, 606026 Russia c N.I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, 603950 Russia *e-mail: [email protected] Received March 10, 2020; revised April 7, 2020; accepted April 9, 2020
Abstract—The dependence of the temperatures of magnetic phase transformations in porous ferromagnetic materials on the geometric characteristics (volume and shape) of pores and their distribution in a particular material has been studied. The geometric features of nanopores have been characterized by their effective pore radius and form factor (deviation of the pore shape from spherical). Estimations indicate that it is possible to obtain macroscopic samples of porous materials with decreased Curie temperatures, which can be further reduced in the case of complicated shapes of pores. These results were obtained in the framework of a cohesive model in application to pure porous nickel and cobalt. Keywords: nanostructuring, porous materials, ferromagnetism, magnetic phase transformations, Curie temperature. DOI: 10.1134/S106378502007024X
In recent years, nanostructured ferromagnetic materials have drawn considerable attention from researchers [1]. This interest is related to both the wide spectrum of possible technological applications of ferromagnetic nanostructures [2] and the variety of phenomena having fundamental significance (see, e.g., [1, 3, 4]). An important parameter characterizing the stability of ferromagnetic material properties is the Curie temperature corresponding to breakage of the magnetic order of a ferromagnet and its transition to a paramagnetic state (second-order phase transition). It is well known that the Curie temperature (and some other parameters [4, 5]) of ferromagnetic nanoscale particles depend on their dimensions [5–8] and shape [7, 8]. This is related to the increasing fraction of lowcoordinated atoms in the near-surface layer with magnetic characteristics (magnetic moments, exchange integrals, magnetic anisotropy constants [5]) that differ from the bulk values. This fraction varies with decreasing size and complicating shape of magnetic nanoparticles. These scaling relations can be taken into account in the framework of significantly different model approaches [1, 5–8]. It should be noted that the formation of nanopowders or nanocomposite materials comprising ferromagnetic nanoparticles distributed in a bulk matrix on a substrate surface [7] is not the only possible approach to obtaining materials with large fractions of near-surface atoms. High values of the specific surface (~500 m3/g [9] or even up to several thousand m3/g
[10]) can also be achieved in materials with distributed ensembles of nanopores in macroscopic obj
Data Loading...
