The role of magnetic domain formation and reorientation processes reveals fascinating physics and is of great relevance for technological applications. Especially the class of magnetic sensors that depend on magnetic thin film technology, rely on magnetic domain control for proper operation. Recent advances in thin film magnetoelectric (ME) composites offer a promising route for sensing ultra-low magnetic signals. Yet, one obstacle of achieving very low limit of detection is caused by magnetic domain activity, which is a well-known noise source in various magnetic field sensing applications. Irreversible and hysteretic magnetization changes from domain nucleation and other hysteretic domain effects impact the sensor’s performance. Moreover, the characteristics of magnetic domains reflect stress induced spatial alterations in the magnetic anisotropy distribution. Overall, due to the formation of magnetic domains in the piezomagnetic phase, the magnetization reversal in magnetic layers is complex.
The role and relevance of magnetic domains and domain walls for the ME response will be discussed in detail. Domain effects in different types of ME devices, including magnetically and electrically modulated thin film devices as well as surface acoustic wave (SAW) devices will be discussed. Domain activity in operating devices is studied from low frequencies, in the hundred kHz range, and at 150 MHz. Domain investigations at the operational frequencies of modulated and SAW sensors are perfomred by time-resolved magneto-optical Kerr effect microscopy.
A direct connection between specific magnetic domain activities and the exhibited noise characteristics is obtained. Even minimal domain activity is restricting magnetic sensor performance. Magnetic noise density and not sensitivity is the main figure-of-merit for optimizing sensor performance. Controlling magnetic domain behavior is a key to improved sensor performance.
Support through the DFG through the Collaborative Research Centre SFB 1261 is highly acknowledged.
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