Investigation and impact of the uniaxial anisotropy formation on the magnetisation dynamics in Fe-Co-Zr-N nanocomposite films for temperature sensor applications

Soft ferromagnetic films with an in-plane uniaxial anisotropy are not merely candidates for micro inductors, transformers noise absorbers or settling EMS problems. They can also be used as a sensor material because they exhibit remarkable property changes if they are exposed to stress and/or temperature [1-2]. One application focuses the control of cutting tools in the metal working industry.
In the present work, Fe40Co37Zr11N12 nanocomposite films were exemplarily deposited on Si-substrates by r.f. magnetron sputtering, in order to investigate their static magnetisation and dynamic magnetic properties on the dependence of the field annealing process, i.e., their formation of the uniaxial anisotropy. The films show a saturation magnetisation of approximately 1.4 T. The annealing process was carried out at different temperatures and annealing time duration. This uniaxial anisotropy influences the low- and high-frequency behaviour regarding the resonance or cut-off frequency and full width of half maximum of the permeability spectrum. As a result, the annealing process shows that a uniaxial anisotropy field µ0.Hu of around 7 mT could be reached, even at 250 °C and 300 °C after an annealing time of about 6000 s. ... mehrBelow that, the uniaxial anisotropy could be conspicuously varied which resulted in different initial permeability values as well as ferromagnetic resonance frequencies in the range between 1.5 and 3 GHz.
When exposing the film to temperatures above room temperature after the conditioning process the permeability changes and the resonance frequency shifts to a lower value. This is due to the change of anisotropy and thermal stress which also influences the anisotropy direction caused by the magnetoelastic effect. The changes of magnetic features can then be utilised as a sensor signal read out by several techniques. One technique can be demonstrated by means of a simple high frequency measuring head in the proximity of the film for non-contact data handling. Another technique is the contactless low frequency mixing method which uses the variation of static magnetisation loops and their resulting static permeability which is described in [3].

[1] K. Seemann, K. Krüger, H. Leiste, J. Mag. Magn. Mater. 369 (2014) 142.

[2] K. Seemann, H. Leiste. M. Stüber, K. Krüger, H. Brunken, A. Ludwig, C. Thede, E. Quandt,
Adv. Eng. Mater. (2016), DOI: 10.1002/adem.201500474.

[3] C. Thede, S. Chemnitz, I. Teliban, C. Bechthold, C. Klever, M. Stüber, E. Quandt, Sens. and
Actuators (2012) A 178 104.