Thermal effects on the magnetic properties of titanium modified cobalt ferrite

The temperature dependence of the magnetic properties of titanium modified cobalt ferrite is presented. The change of maximum magnetization obtained at H ≈ 2.4 MA/m between any two temperatures increases systematically with composition, which is desirable for applications in devices. Variation in magnetocrystalline anisotropy and coercivity were different from previous studies on cation substituted cobalt ferrite. At lower concentrations, the effect of lower thermal energy dominated the effect of non-magnetic cation substitutions in controlling the anisotropy.The reverse was the case at higher concentrations. The temperature dependence of coercivity is dominated by the contribution of magnetocrystalline anisotropy to coercivity, while the compositional dependence of coercivity is dominated by microstructural contribution through the pinning of domain walls

Temperature dependence of magnetic properties of heat treated cobalt ferrite

This study demonstrates the effectiveness of heat treatment in optimizing the magneticproperties of cobalt ferrite, compared to other methods such as cation substitution. It also shows how the magnetic properties of the heat treated cobalt ferrite vary under differenttemperature conditions. Saturation magnetization increased more due to heat treatment than due to Zn-substitution; a cation substitution that is known to result in high saturationmagnetization in ferrites. A remarkable observation is that the increase in the saturationmagnetization due to heat treatment was not at the expense of Curie temperature as was often reported for cation substituted materials. The observed variations in the magnetic propertieswere explained on the basis of cation redistribution arising as a result of the heat treatment

Addressing Criticality in Rare Earth Elements via Permanent Magnets Recycling

Rare earth elements (REEs) are critical for many advanced technologies and are faced with potential supply disruptions. Recycling of permanent magnets (PMs) can be good sources for REEs which can help minimize global dependence on freshly mined REEs, but PMs are rarely recycled. Recycling of PMs has been discussed with respect to improving REEs resource sustainability. Some challenges to be addressed in order to establish industrially deployable technologies for PMs recycling have also been discussed, including profitability, energy efficiency and environmental impacts. Key considerations for promoting circular economy via PMs recycling is proposed with the focus on deciding the target points in the supply chain at which the recycled products will be inserted. Important technical considerations for recycling different forms of waste PMs, including swarfs, slags, shredded and intact hard disk drives magnets, have been presented. The aspects of circular economy considered include reusing magnets, remanufacturing magnets and recovering of REEs from waste PMs

Some Tests for Seasonality in Time Series Data

This paper presents some tests for seasonality in a time series data which considers the model structure and the nature of trending curve. The tests were applied to the row variances of the Buys Ballot table. The student t-test and Wilcoxon Signed-Ranks test have been recommended for detection of seasonality

Barkhausen spectroscopy: Non-destructive characterization of magnetic materials as a function of depth

In this study, we conceptually divided a ferromagnetic specimen into layers along its depth. For each layer, we derived a non-linear integral equation that describes the attenuation with frequency and distance of magnetic Barkhausen emissions coming from that layer. We postulate that the Barkhausen spectrum measured at the surface by an induction coil can be expressed as the sum of the individual layer spectra. We show how a non-linear least squares algorithm can be used to recover the properties in individual layers. These are related to stress using an extension to the theory of ferromagnetic hysteresis. We found that the quality of the fit is influenced by the sensitivity of the ferromagnetic material to strain, as well as by the sensor-specimen coupling. The proposed method can be used for the non-destructive characterization of stress as a function of depth in magnetic materials

Time series modeling of Nigeria external reserves

This paper discusses the levels and trend of external reserves in Nigeria. The relevance of this lies in the fact that it could help to monitor the reserves and throw early warning signal about any economic crisis. Monthly data on Nigeria external reserves for the period January 1999 to December, 2008 derived from the 2008 CBN Statistical Bulletin was analyzed using ARIMA model. Results of the analyses show that (i) the data requires logarithmic transformation to stabilize the variance and make the distribution normal (ii) the appropriate model that best describes the pattern in the transformed data is the Autoregressive- Integrated Moving Average process of order (2,1,0). This model is recommended for use until further analysis proves otherwise

Developments in deep brain stimulation using time dependent magnetic fields

The effect of head model complexity upon the strength of field in different brain regions for transcranial magnetic stimulation (TMS) has been investigated. Experimental measurements were used to verify the validity of magnetic field calculations and induced electric field calculations for three 3D human head models of varying complexity. Results show the inability for simplified head models to accurately determine the site of high fields that lead to neuronal stimulation and highlight the necessity for realistic head modeling for TMS applications

Approach for Improving the Sensitivity of Barkhausen Noise Sensors with Applications to Magnetic Nondestructive Testing

Barkhausen noise emissions occur in ferromagnetic materials on application of a time varying external magnetic field. These emissions primarily occur because of the movement of domain walls in the presence of pinning sites or discontinuities, which act as inhibitors to domain wall motion within the material. The emissions can be sensed using an induction coil placed close to the sample surface. The coil can sense the variations in magnetic flux, which translates to the induced electromagnetic field. This study optimizes the design of the barkhausen noise sensor via finite element simulations. The different parameters involved in improvement of the design of the barkhausen noise sensor are discussed

Investigation of the structure, magnetic and magnetoelastic properties of cobalt ferrite and its derivatives

In this research, cobalt ferrite thin films were deposited at 523 K which eliminates the need for annealing at higher temperatures and offers hope for integration of the thin films into micro-electromechanical devices.EThOS - Electronic Theses Online ServiceGBUnited Kingdo