Nanoparticle Size Threshold for Magnetic Agglomeration and Associated Hyperthermia Performance

The likelihood of magnetic nanoparticles to agglomerate is usually estimated through the ratio between magnetic dipole-dipole and thermal energies, thus neglecting the fact that, depending on the magnitude of the magnetic anisotropy constant (K), the particle moment may fluctuate internally and thus undermine the agglomeration process. Based on the comparison between the involved timescales, we study in this work how the threshold size for magnetic agglomeration (daggl) varies depending on the K value. Our results suggest that small variations in K-due to, e.g., shape contribution, might shift daggl by a few nm. A comparison with the usual superparamagnetism estimation is provided, as well as with the energy competition approach. In addition, based on the key role of the anisotropy in the hyperthermia performance, we also analyse the associated heating capability, as non-agglomerated particles would be of high interest for the application.

Investigation of Magnetic Properties of Magnetic Poly (glycidyl methacrylate) Microspheres: Experimental and Theoretical

Biocompatible magnetic poly (glycidyl methacrylate) microsphere is a novel nanocomposite with a myriad of promising bioapplications. Investigation of their characteristics by experimental analysis methods has also been carried out in the past. However, a survey of the magnetic anisotropy constant has not been mentioned and the influence of the poly (glycidyl methacrylate) polymer matrix on the Fe3O4 magnetite nanoparticles embedded inside has also not been discussed. Moreover, the accurate characterization of the magnetite nanoparticle size distribution remains challenging. In this paper, we present an effective approach was used to solve these problems. First of all, we combine both experiment and theory to estimate the effective magnetic anisotropy constant. Besides that, we implement an accurate method to determine magnetite nanoparticle size distribution in the magnetic poly (glycidyl methacrylate) microspheres composite nanomaterial.

Multiscale Magnetic Anisotropy in Amorphous Ferromagnetic Ribbon: An Example of FeCuNdSiB Alloy

An understanding of the magnetic properties in an amorphous alloy requires comprehensive studies of magnetic anisotropy at various scales. In this paper such a study is carried out using amorphous ribbons FeCuNbSiB. The magnetic anisotropy associated with the rolling axis of ribbons does not affect hysteresis loop measurements, but the disappearance of a fingerprint-like pattern in the domain structure occurs in different fields when they are applied along and transverse the rolling axis. A correlation between the local magnetic anisotropy constant and the nanoscale within which the local easy axis is ordered was found.

Surface and Microstructure Analysis of CoCrPt Film on RuCoCrX (X = Ti, Re) Intermediate Layers

The microstructural and magnetic properties of perpendicular anisotropic CoCrPt films deposited on Ru or RuCoCrX (X = Ti, Re) intermediate layers were studied. The c-axis of CoCrPt grains were promoted by (0002) textured RuCoCr, and RuCoCrX (X = Ti, Re) intermediate layers due to smaller lattice misfit as compared to Ru. The narrower rocking width (Δθ50 = 3.76°) in RuCoCrRe intermediate layer and CoCrPt shows higher out of plane coercivity (Hc = 6.2 kOe), magnetic anisotropy constant (Ku = 6.2 × 106 erg/cm3) and nucleation field (HN = −2.8kOe) as compared to the Ru intermediate layer (Hc = 5.4 kOe, Ku = 5.9 × 106 erg/cm3, HN = −1.6 kOe). The partial intergranular exchange decoupling of CoCrPt grains was observed. The grain boundaries oxides were formed by the residual oxygen in targets and sputtering processes. The minor Cr2O3, CoO, TiO2, ReO3 oxides were investigated by surface analysis. Due to the minor oxides and Cr segregation at grains boundaries, the CoCrPt films present high coercivity. Samples CoCrPt/RuCoCr and CoCrPt/RuCoCrTi present a minimum at 45° but the values are much higher than the ideal Stoner-Wohlfarth theoretical value 0.5 which could be due to fewer natural oxides for magnetic grains separation. In sample CoCrPt/RuCoCrRe, there is an increase of intergranular interaction as indicated by the large asymmetry and the shift of the minimum at lower angles.

Влияние дисперсии магнитной анизотропии кластеров Ge-=SUB=-3-=/SUB=-Mn-=SUB=-5-=/SUB=- на температурные зависимости намагниченности тонких пленок Ge:Mn

The temperature dependences of magnetization M ( T ) of thin ion-implanted Ge:Mn (4 at % Mn) films containing Ge_3Mn_5 clusters were measured on samples cooled in the absence of magnetic field (zero field cooled, ZFC) and in a magnetic field of 10 kOe (field-cooled, FC). It has been established that the shape of ZFC–FC differential M ( T ) curves is determined by lognormal distribution of the size-dependent magnetic anisotropy energy of Ge_3Mn_5 clusters. Analysis of the observed ZFC–FC magnetization curves allowed the magnetic anisotropy dispersion (variance) and magnetic anisotropy constant to be estimated.