Magnetic Properties of Nanostructured Materials

Abstract

Understanding the correlation between magnetic properties and nanostructure involves collaborative efforts between chemists, physicists, and materials scientists to study both fundamental properties and potential applications. This article introduces a classification of nanostructure morphology according to the mechanism responsible for the magnetic properties. The fundamental magnetic properties of interest and the theoretical frameworks developed to model these properties are summarized. Common chemical and physical techniques for the fabrication of magnetic nanostructures are surveyed, followed by some examples of recent investigations of magnetic systems with structure on the nanometer scale. The article concludes with a brief discussion of some promising experimental techniques in synthesis and measurements.

Ferromagnetism in Fe-doped ZnO nanocrystals: Experiment and theory

“…5͑a͒, which indicates a considerable amount of relaxation within a time period of 7000 s. This curve rules out the possibility of cusp behavior in the ZFC curve due to superparamagnetic behavior as for superparamagnetic systems the relaxation is very fast, within the experimental time scale of hundreds of seconds. 55 Also, the time dependence of the thermoremanent magnetization can be fitted well with a stretched exponential function M͑t͒ = M 0 + M r exp͓−͑t / ͒ 1−n ͔, where M 0 is related to the intrinsic ferromagneticlike component and M r relates to a glassy component contributing to the observed relaxation effect. The time constant and the parameter n are related to the relaxation rate.…”

“…For superparamagnetic systems, as is well known, the curves merge into a single one. 43,55 This rules out the possibility of thermal-energyinduced spontaneous magnetization reversal as happens in the case of an assembly of single-domain particles leading to superparamagnetic behavior. More convincingly, the superparamagnetic limit for Fe-doped systems can be calculated by the expression for the relaxation time = 0 exp͑E A V / k B T͒, where the anisotropy energy density E A has a value of 5 ϫ 10 4 J/m 3 for Fe, and V and k B are the particle volume and Boltzmann constant, respectively.…”

Large-Pore Mesoporous Ho3Fe5O12 Thin Films with a Strong Room-Temperature Perpendicular Magnetic Anisotropy by Sol–Gel Processing

“…They are constantly undergoing changes to adapt to modern device requirements and, in recent years particularly, magnetic nanostructures have been in the focus of interest, with much attention paid to size and orientation effects. [1][2][3] Many routes to achieving nanoscale materials with different morphologies, including wires, particles, and thin films, to mention only a few, have been reported in the literature. [4][5][6] Among them are solution-processing routes such as solvothermal and sol-gel methods, physical deposition techniques, mechanochemical approaches, and others.…”

Drastic improvement in magnetization of CdO nanoparticles by Fe doping

“…These lengths are predominantly in the order of 1-100 nm (Leslie-Pelecky and Rieke 1996;Holz and Scherer 1994). Here, in this case, the most effective magnetic length is the crystalline anisotropy one which depends mainly on the anisotropy constant.…”