Determination of magnetic characteristics of nanoparticles by low- temperature calorimetry methods

Author: romani abramishvili
Keywords: nanoparticle, Mechanical anisotropy, superparamagnetism.
Annotation:

Over the past decades, the field of research and development of physical characteristics of magnetic nanomaterials has undergone dramatic changes. This is due to the development of efficient methods for preparation and stabilization of nanometer sized magnetic particles (nanoparticles), and to the development of physical methods for their investigation [1–3]. When reducing the particle to a single domain size, the impact of thermal fluctuations on the rotational dynamics of the magnetic moment m of nanoparticles begins to grow. This type of the random motion of the magnetic moment is called superparamagnet- ism, and the system consisting of macroscopic amounts of this type of nanoparticles – a superparamagnetic. One of the distinguishing features of superparamagnetics from conventional paramagnetic materials is that not individual atoms (or molecules) are carriers of the magnetic properties of elementary particles contained therein but magnetic nanoparticles containing a large number of atoms in the magnetically ordered state. The magnetic moments of nanoparticles are much larger than the magnetic moments of single particles of a conventional paramagnetic of the order of only a few Bohr magnetons. Another distinguishing feature of superparamag- netics is related to the presence of the magnetic anisotropy energy of their particles. The magnetic characteristics of bulk samples – the anisotropy ratio A and the magnetic moment m – depend on the volume [4]. However, in the nanostructured magnetic particles A and m, the characteristics, besides the volume, also depend on the surface area of the nanoparticle ⁎ Corresponding author. E-mail address: simon.chkhaidze@tsu.ge (S. Chkhaidze). http://dx.doi.org/10.1016/j.physb.2017.03.011 Received 26 April 2016; Received in revised form 1 February 2017; Accepted 3 March 2017 Available online 06 March 2017 0921-4526/ © 2017 Elsevier B.V. All rights reserved. [5]. The surface contribution complicates significantly the development of theoretical methods for calculating these characteristics. The known numerical values of the magnetic characteristics were obtained by measuring the blocking temperature [6], or are known from the experiments with cluster beams [7] and the total magnetization relaxation studies [8]. In recent years, to determine the macroscopic characteristics of materials (including superparamagnetics), the adiabatic calorimetry allowing precise determination of the temperature dependence of the heat capacity has been successfully used [9–18]. In [19], the idea of determining the magnetic anisotropy constant by high-precision low- temperature calorimetry methods has been suggested. In this paper, methods for determining the magnetic characteristics (coefficient of anisotropy and magnetic moment) of nanoparticles by means of low- temperature heat capacity measurements are developed.

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ნანონაწილაკის მაგნიტური მახასიათებლების განსაზღვრა დაბალტემპერატურული კალორიმეტრიის მეთოდებით. [ka]