Magnetic properties of Ho2Fe17-xMnx - Influence of Mn substitution
The structural and magnetic properties of Ho2Fe17−xMnx (x=0−5) have been investigated by x-ray diffraction, Mossbauer spectroscopy and DC magnetization measurements (0-5 T) over the temperature range 4.5–350 K. Similar to other ferrimagnetic R2Fe17−xMnx systems, the unit cell volume generally increases with Mn content other than for low Mn values where a slight maximum is detected around x ~ 0.5. The nature of the magnetic phase transitions around TC is shown by Arrot plot analysis to be second order for all samples. The Curie temperature remains essentially unchanged for Mn contents up to x=1.0 (TC = 336 K for x=0.0, TC = 338 K for x=1.0) before decreasing steadily with further increase in Mn content (TC = 209 K for x=5). The 57Fe hyperfine interaction parameters have been determined from variable temperature Mossbauer spectra.
Critical behaviour of Ho2Fe17 − xMnx—magnetisation and Mössbauer spectroscopy
The magnetic properties of Ho2Fe17 − xMnx compounds (x = 0–2) of ferromagnetic ordering temperatures up to TC ~344 K have been investigated by DC magnetization and Mössbauer effect measurements. The nature of the magnetic phase transitions and the critical behaviour around TC has been investigated by analysis of the magnetisation data and the critical exponents β, γ and δ determined. The critical exponents are found to be similar to the theoretical values of the mean-field model for which β = 0.5 and γ = 1.0, indicating the existence of a long-range ferromagnetic interactions. The isothermal entropy changes ΔS around TC have been determined as a function of temperature in different magnetic fields.
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.