Flexible magnetic Ni 80 Fe 20 thin films with excellent adhesion, mechanical and magnetic properties have been fabricated using magnetron plasma deposition. We demonstrate that flexible Ni 80 Fe 20 thin films maintain their non-flexible magnetic properties when the films are over 60 nm thick. However, when their thickness is reduced, the flexible thin films display significant increase in their magnetic coercive field compared to identical films coated on a solid Silicon substrate. For a 15 nm flexible Ni 80 Fe 20 film coated onto 110µm Polyvinylidene fluoride polymer substrate, we achieved a remarkable 355% increase in the magnetic coercive field relative to the same film deposited onto a Si substrate. Experimental evidence, backed by micro-magnetic modelling, indicates that the increase in the coercive fields is related to the larger roughness texture of the flexible substrates. This effect essentially transforms soft Ni 80 Fe 20 permalloy thin films into medium / hard magnetic films allowing not only mechanical flexibility of the structure, but also fine tuning of their magnetic properties.
In this paper, the magnetoelectric (ME) characteristics of bar and plate structures of the nano bi-layer ME materials are investigated and compared. The mathematical models of ME coefficients of the nano bi-layer bar and plate structures operated in the longitudinal-transverse (L-T) mode are developed using the constitutive equations and Newton’s second law. The nano bi-layer of interest consists of Terfenol-D and Lead Zirconate Titanate (PZT) as ferromagnetic (FM) and ferroelectric (FE) phases, respectively. In the low frequency regime, the optimal thickness ratios of bar and plate structures that yield maximum ME coefficients are around 0.43 and 0.33, respectively. The optimal thickness ratios are applied in the high frequency regime to obtain the conditions where the maximum ME coefficients can be achieved. It is found that the resonant frequencies of the bar and plate structures decrease exponentially with the bi-layer length and thickness, respectively. The results also indicate that at the same resonant frequency, the dimension of the bar structure is significantly smaller than the plate structure, it thus becomes more preferable for nano scale sensing applications.
Recently, the magnetoelectric (ME) effect is widely studied to apply in sensing applications. This paper proposes the investigation of ME effect in the bi-layer plate structure, which is the structure that allows deformation in the thickness direction. Mathematical models of the ME coefficients are developed using the constitutive equations of magnetostrictive and piezoelectric. Two modes of interest include longitudinal-transverse (L-T) and transverse-transverse (T-T) modes. Applying the models to the nanolayer of Terfenol-D/PZT in the assumingly low frequency regime yields the optimal thickness ratio of 0.34 for both modes. The maximum ME coefficients for 5, 10, and 10 nm thick structures are equal but occur at different resonant frequencies. They are approximately 480 and 240 mV/Oe cm for T-T and L-T modes, respectively. The maximum ME coefficients of the Terfenol-D/PZT plate structure are sufficiently high for nanoscale magnetic sensing applications.
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