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Tunneling magnetoresistive (TMR) sensors can precisely measure magnetic fields, being a key element in next-generation highly sensitive angular positioning systems. Still, when fields are applied in directions that differ from the easy axis, the interplay between all magnetic contributions becomes crucial. In this work, we investigate the angular-dependent output of TMR sensors, when operating under a field that saturates the free layer (FL). We have used synthetic antiferromagnets (SAFs) with tuned antiferromagnetic $(\Delta H)$ by changing the ferromagnetic (FM) layer thicknesses. The reference layer (RL) reversal field $\left({H}_0^{+}\right)$ was set between 57 and 260 mT. The results show that these SAF characteristics affect the angular-dependent FL saturation field, showing differences up to ≈6 mT when changing SAF magnetic moment. From $R(H, \theta)$ , and using a macrospin model, we evaluate the magnetization misalignment in-between FM layers. For the SAF with higher H+−, deviations up to 10°, are seen when operating at 100 mT $\ll H_0^{+}$ . Noticeably, we also observed a nonnegligible contribution of the SAF magnetization reversal to $R(H, \theta)$ even at the low external fields of 20 mT, with the deviations of ≈1° from ideal behavior, which is often overlooked. This study links the observed resistance deviations to specific magnetic couplings and intrinsic anisotropies. With this information, we are able to design the multilayers for controlled output inaccuracies or according to the maximum allowed errors in the application. Ultimately, an optimal saturation magnetic field is obtained to deliver the best angular performance in the TMR elements.

Encoding information in patterns printed with magnetic ink can extend the usability of barcode and QR code technologies to applications that do not require a line of sight between the sensor and the code. Such an implementation garners an interest in security, track-and-trace, and recyclable packaging applications. Previous work has demonstrated a device that can read a barcode obscured by a layer of opaque and 1 mm thick material. However, given that the most widespread magnetic toners are soft magnetic, a permanent magnet (PM) is needed in the system alongside the sensor to magnetically bias the barcode, which affects the sensor sensitivity. Here, we describe a protocol to evaluate the impact of different PM geometries on the performance of the sensor and validate it with experimental results, enabling active feedback for integration in the scanner system. As a result, we have reached an improved geometry that increases the reading distance of the device to at least 2 mm. This study is also useful for other applications that require optimization of the interaction between a PM and a magnetic sensor (e.g., nanoparticle tracking in magnetoresistive biosensors).