Comparison of Sensitivity and Low-Frequency Noise Contributions in Giant-Magnetoresistive and Tunneling-Magnetoresistive Spin-Valve Sensors with a Vortex-State Free Layer (original) (raw)
Related papers
Giant magnetoresistive spin valve bridge sensor
IEEE Transactions on Magnetics, 1996
We describe the design, fabrication, and performance of a "spin valve" magnetic field sensor based on the giant magnetoresistive effect. The sensor is a balanced, four resistor, fully biased, Wheatstone bridge network with bipolar output. The devices described here show magnetoresistance ratios AV/V = AR/R = 6%, saturation fields of 25 Oe, and a Johnson limited noise floor of 2.6 pOe/(Hz)"2. The linearity of the device is +/-2% of the full scale amplitude, with a hysteresis of 1% over the linear range. Fabrication of this device requires a novel approach to setting the directions of the antiferromagnetic exchange layers that bias the sensor. As compared to bridges based on the anisotropic magnetoresistance effect, these devices offer superior signal amplitude and linearity. To our knowledge this is the first report of such a device.
Journal of Physics-condensed Matter, 2007
Magnetoresistive sensors using spin valves and magnetic tunnel junctions are reviewed, considering applications as readers in hard disk drives, as well as applications where the ultimate field detection limits are required (from nT down to pT). The sensor noise level in quasi-DC or high-frequency applications is described, leading to sensor design considerations concerning biomedical and read head applications. Magnetic tunnel junction based sensors using MgO barriers appear as the best candidates for ultra-low field (pT) detection, either in the high-frequency regime, or for quasi-DC applications.
IEEE Transactions on Magnetics, 2007
The magnetic field detection limit of spin valve sensors in the thermal noise regime is improved from 1.3 nT/Hz 1 2 to 0.064 nT/Hz 1 2 by incorporating a Co 93 Zr 3 Nb 4 soft magnetic flux guide concentrator structure. Linear spin valve sensors were processed down to 20 2 m 2 dimensions, with and without an additional 3500-Å-thick flux guide concentrator, with a magnetic flux gain factor ranging from 5 to 20. Spin valves show a starting sensitivity of 0.2 %/Oe, improved to 3.8 %/Oe with the flux concentrator. Noise measurements from dc to 500 kHz were performed, indicating similar noise levels with and without flux concentrators. In terms of magnetic field detection, sensors with flux concentrators show a detection limit of 2 nT/Hz 1 2 at 10 Hz, compared to 47 nT/Hz 1 2 without flux concentrators.
Journal of Science: Advanced Materials and Devices, 2018
The main magnetoresistive properties of pinned spin valves (SV) and their roles in lowfield magnetic sensing applications were characterized. The performances of the magnetoresistive properties were extracted, including the exchange bias (H eb) field as a function of iron content in the CoFe layer and the antiferromagnetic (AFM) thickness, the magnetoresistance (MR) ratio versus the spacer thickness, the coercivity (H c) as a function of the seed layer and composite layer [NiFe/Co] used. The above properties of the SV films were the crucial parameters deciding the features of the low-field magnetic sensors. Eventually, a selected SV film structure was found to be (Si/SiO 2)/Ta(50)/[NiFe(30)/Co(15)]/Cu(24)/Co 80 Fe 20 (25)/IrMn(100)/Ta(50), and SV elements were patterned using the lithographic lift-off method with the active cell dimension of 2 µm × 150 µm. To define a pinning axis, a cool-field anneal was used at 250 for 30 minutes in a magnetic field of 2 kOe. A Wheatstone half bridge was engineered using two SV elements and two external resistances. The operation point of the sensor was well tuned using a tiny permanent magnet. A sensitivity of 5 V/T was observed with a linear range of ± 2 mT. To demonstrate the performance of the designed sensor, a measurement of the Earth magnetic field was carried out. The engineered SV sensor could be used in low-field magnetometer and electronic compass applications.
Magnetoresistance sensors with magnetic layers for high sensitivity measurements
In this study we present an overview of the sensors made from magnetic layers and nanostructured systems. Fundamental and technological aspects are presented. A review of the spin valve mechanism is presented. A spin valve device consists of two ferromagnetic layers, separated by a Cu spacer. When the Cu layer is replaced by a thin insulator layer (Al2O3) then, we have a magnetic tunnel junction or, for some deposition conditions, a nanogranular system. Electrical and magnetic characterization of the magnetic layers and nanogranular systems plays an important role in the designing process of these sensors and some results are presented in this paper. For a better understanding of the magnetization processes that take place in these systems, micromagnetic simulations were performed as well. Finally, we present a method to increase the response quality of a rotation sensor based on the anisotropic magnetoresistance effect and a detection system of the magnetic particles employed in biology as markers or as carriers for targeted drug delivery.
Developments and applications of tunneling magnetoresistance sensors
Tsinghua Science and Technology, 2022
Magnetic sensors based on tunneling magnetoresistance (TMR) effect exhibit high sensitivity, small size, and low power consumption. They have gained a lot of attention and have potential applications in various domains. This study first introduces the development history and basic principles of TMR sensors. Then, a comprehensive description of TMR sensors linearization and Wheatstone bridge configuration is presented. Two key performance parameters, the field sensitivity and noise mechanisms, are considered. Finally, the emerging applications of TMR sensors are discussed.
Magnetization processes in spin-valve meanders for sensor applications
IEEE Transactions on Magnetics, 2003
We used Kerr microscopy to investigate the magnetization processes of NiFe-Co/Cu/Co/ FeMn spin-valve meanders for magnetoresistive sensors and compared them to processes in related single films and bilayers. We observed irregular switching, characterized by the irreversible decay of blocked domains or by domain nucleation at 360 walls, in the related films and in the free layer of the spin-valve system. Both effects are connected with hysteresis. Edge-curling walls are responsible for rotational hysteresis in the giant magnetoresistance signal of the spin valves, occurring during field rotation in clockwise and counterclockwise directions. The U-turns of the meanders and their shape have no relevant influence on the magnetization behavior and hysteresis effects.