Magnetic Nanoparticles with Core Shell: Macroscopic Model and Coercive Field

Abstract

There exists nonhomogeneous structure in mechanosynthesized nanoparticles consisting of an ordered core surrounded by the shell. The shell may be structurally and magnetically disordered, or it may be ordered. These nanoparticles are found to be roughly spherical. We formulate the macroscopic model for the description of magnetic properties of nanoparticles with core-shell structure. The case of spheroids oriented in the same direction of polar axes is considered. There exits two coercive fields:HcγandHcψ. They are depending on quantitiesoandx, wherex=V2/(V1−2V2), ando=IF/IS, hereV1is the volume of the nanoparticle, andV2is the volume of the core.IFis the magnetization of the core, andISis the magnetization of the shell. There exists a transition from one type of the coercive field to another, changingxando. We have found qualitative explanation of observed enhancement of coercive field and of itsd-dependence inNiFe2O4nanoparticles.

Tuning the Magnetic Properties of Nanoparticles

“…In the case of a magnetic coating, the core-shell interface interaction might lead to a change in anisotropy and a shift in the hysteresis loop. The shift of the hysteresis loop is “exchange bias” and it mainly arises due to interface coupling between two different types of layers (e.g., ferromagnetic and ferrimagnetic) [113,114]. The discussion that follows focuses on the impact of various types of coatings on the magnetic properties of surface-modified MNPs.…”

Co3O4-γ-Fe2O3Nanocrystal Heterostructures with Enhanced Coercivity and Blocking Temperature

“…To estimate the blocking temperature, T B , FC−ZFC curves were measured between 2 and 400 K (Figure 5C The enhanced H C observed in the Co 3 O 4 −γ-Fe 2 O 3 heterostructures originates from the effect of interface coupling between ferrimagnetic and antiferromagnetic components. 5,6,[10][11][12][13][14][15][16]42,43 As Co 3 O 4 has a T N of 41 K in the bulk form, 44 one would expect the T B of the heterostructures not to be increased beyond this temperature. However, it has been shown in other systems that the T B of FM−AFM hybrids could be increased well above the T N of the AFM component by suitable morphology control.…”

“…The enhanced H C observed in the Co 3 O 4 –γ-Fe 2 O 3 heterostructures originates from the effect of interface coupling between ferrimagnetic and antiferromagnetic components. ,,− ,, As Co 3 O 4 has a T N of 41 K in the bulk form, one would expect the T B of the heterostructures not to be increased beyond this temperature. However, it has been shown in other systems that the T B of FM–AFM hybrids could be increased well above the T N of the AFM component by suitable morphology control. , The field-cooled hysteresis loop measured at 5 K for the Fe-rich Co 3 O 4 –γ-Fe 2 O 3 heterostructure (Figure S5) shows a very low exchange bias of 17 mT.…”

Luminescence Nanothermometry Based on Pr3+ : LaF3 Single Core and Pr3+ : LaF3/LaF3 Core/Shell Nanoparticles

“…Usually, the core serves as a scintillator, and the shell plays such screening "defensive" role although a set of functions of both core and shell can be more complicated [11,26,27]. In order to synthesize such core/shell NPs, the conventional coprecipitation [28] and hydrothermal methods [29] of synthesis have successfully been adopted during the last decade.…”