Interview Questions for Giant Magnetoresistance Properties

Giant Magnetoresistance (GMR) is a quantum mechanical phenomenon where the electrical resistance of a material changes significantly in the presence of a magnetic field. Imagine a tiny highway for electrons. In a GMR structure, this highway is composed of alternating magnetic and non-magnetic layers. When the magnetic layers are aligned (parallel), electrons flow smoothly – low resistance. When they’re misaligned (antiparallel), the electrons encounter significant ‘traffic jams’ – high resistance. This dramatic change in resistance, proportional to the applied magnetic field, is the essence of GMR.

More technically, GMR arises from the spin-dependent scattering of conduction electrons. The electrons have an intrinsic property called ‘spin’, which can be thought of as an internal angular momentum. In ferromagnetic layers (materials with spontaneous magnetization), electrons with spins aligned parallel to the magnetization experience less scattering than those with antiparallel spins. The layered structure cleverly exploits this difference to achieve a significant change in resistance.

Both GMR and Anisotropic Magnetoresistance (AMR) describe changes in electrical resistance due to a magnetic field, but they differ significantly in their origin and magnitude. AMR is an intrinsic property of ferromagnetic materials, meaning the resistance change is relatively small and depends on the angle between the magnetization direction and the current flow. Think of it like a slightly bumpy road where the bumps influence the speed of your car depending on the direction you drive. The effect is subtle.

GMR, on the other hand, is a much larger effect resulting from the interplay of spin-dependent scattering in multiple layers. It depends on the relative orientation of magnetization in adjacent ferromagnetic layers, not just the angle. In our highway analogy, GMR is like encountering a major traffic jam depending on whether the neighboring highways are aligned. The difference in resistance is orders of magnitude larger than in AMR.

GMR devices typically utilize a combination of ferromagnetic and non-ferromagnetic materials. Common ferromagnetic materials include:

• Iron (Fe): A readily available and relatively inexpensive ferromagnetic material.
• Cobalt (Co): Offers higher magnetization and better magnetic properties in some applications.
• Nickel (Ni): Often used in alloys with Fe and Co to fine-tune magnetic properties.

Non-ferromagnetic materials, also called spacer layers, commonly used are:

• Chromium (Cr): Frequently employed due to its antiferromagnetic properties in certain thicknesses.
• Copper (Cu): Offers excellent conductivity and facilitates electron transport between the ferromagnetic layers.
• Non-magnetic alloys: Various other alloys are sometimes used to further optimize the GMR effect.

The layer structure is absolutely critical to the GMR effect. The precise thickness and arrangement of ferromagnetic and non-ferromagnetic layers directly influence the magnitude of the resistance change. Too thick a non-magnetic layer will reduce the interaction between ferromagnetic layers, weakening the GMR effect. Too thin, and other issues may arise that reduce efficiency.

The number of layers also plays a role. More complex multilayers can lead to enhanced GMR, but optimizing this requires sophisticated fabrication techniques. Furthermore, the interface quality between layers is crucial. Atomic-scale imperfections can severely degrade the GMR response. Careful control over the deposition process is necessary to ensure sharp interfaces and optimal layer thicknesses.

Antiferromagnetic (AFM) layers, such as certain thicknesses of chromium, play a crucial role in many GMR devices, particularly spin valves. They don’t contribute directly to the GMR effect but provide an important function: pinning the magnetization of one of the ferromagnetic layers.

Imagine trying to align two magnets. It’s much easier if one magnet is fixed in place. The AFM layer acts as a ‘pin’ for one ferromagnetic layer, ensuring its magnetization remains fixed regardless of an external field. This makes the other ferromagnetic layer’s magnetization more sensitive to small external fields, significantly improving the sensitivity of the GMR sensor.

Several key architectures exploit GMR. Two prominent examples are:

• Spin Valves: These consist of a pinned ferromagnetic layer (pinned by an AFM layer), a non-magnetic spacer layer, and a free ferromagnetic layer. The resistance changes dramatically depending on whether the magnetization of the free layer is parallel or antiparallel to the pinned layer.
• Magnetic Tunnel Junctions (MTJs): MTJs use an insulating barrier (e.g., MgO) between two ferromagnetic layers. Electron tunneling through the barrier is spin-dependent, leading to a large change in resistance when the magnetizations are parallel versus antiparallel. MTJs generally exhibit much larger GMR than spin valves, but their fabrication is more complex.

The choice between these architectures depends on factors like desired sensitivity, manufacturing cost, and application requirements.

GMR sensors offer several advantages:

• High sensitivity: They can detect very small magnetic fields, enabling applications requiring high precision.
• Fast response time: They respond quickly to changes in magnetic fields.
• Compact size: They can be miniaturized, making them suitable for various applications.
• Low power consumption: Generally consume less power compared to other sensing technologies.

However, there are also some disadvantages:

• Temperature sensitivity: The GMR effect can be affected by temperature fluctuations, potentially requiring temperature compensation.
• Fabrication complexity: Creating high-quality GMR devices requires sophisticated thin-film deposition techniques.
• Cost: While costs have decreased, GMR sensors can be more expensive than some other sensor technologies.

Giant Magnetoresistance (GMR) revolutionized hard disk drive (HDD) technology by enabling significantly higher storage densities and faster read speeds. Before GMR, HDD read heads relied on inductive techniques, which were limited in sensitivity and resolution. GMR read heads, however, utilize the change in electrical resistance of a multilayer thin film structure in response to an applied magnetic field. This allows for the detection of much weaker magnetic fields emanating from the tiny magnetic bits on the hard disk platter.

Imagine trying to read tiny writing with a dim flashlight versus a powerful laser. The inductive read heads were like the dim flashlight – they struggled to discern the magnetic bits. GMR read heads, however, are like the powerful laser, easily detecting even the faintest magnetic signals. This significant improvement in sensitivity allowed for a dramatic increase in data storage capacity.

In essence, the GMR read head senses the direction of magnetization of the magnetic bits on the hard disk platter. This direction represents the stored data (0 or 1). The change in resistance of the GMR sensor, caused by the magnetic field from the bits, is measured and translated into the corresponding digital data.

GMR plays a crucial role in various magnetic sensors due to its high sensitivity to even weak magnetic fields. This sensitivity allows for the precise measurement of magnetic field strength, direction, and changes in these parameters. This capability is exploited in a vast array of applications.

• Current Sensors: GMR sensors can accurately measure the current flowing through a conductor by detecting the magnetic field generated around it. This is particularly useful in power management and industrial monitoring.
• Position Sensors: By utilizing a permanent magnet and a GMR sensor, the relative position or movement of the magnet can be determined with high accuracy. This is widely used in automotive applications, robotics, and industrial automation.
• Angle Sensors: Similar to position sensors, angle sensors use the rotation of a magnet to measure angular displacement. Applications include navigation systems and motor control.
• Biomagnetic Sensors: The high sensitivity of GMR allows for the detection of very weak magnetic fields generated by biological processes, like those in the human brain (Magnetoencephalography or MEG).

The key advantage of GMR in these sensors is their ability to provide a precise and reliable measurement of magnetic fields with minimal power consumption and a compact form factor.

Temperature significantly impacts GMR. The GMR effect is temperature-dependent, with the magnitude of the magnetoresistance typically decreasing as temperature increases. This is because higher temperatures enhance spin scattering and reduce the spin polarization of the electrons, both key factors in the GMR effect. Imagine a highway with smooth traffic (low temperature, strong GMR). As temperature rises, the traffic becomes congested (increased spin scattering), leading to reduced efficiency (reduced GMR).

This temperature dependence necessitates careful design considerations for GMR devices. Strategies to mitigate this effect include using materials with reduced temperature sensitivity or incorporating temperature compensation circuitry in the device design. For instance, specialized materials and multilayer structures have been developed to minimize the impact of temperature variations and ensure stable sensor performance over a wide range of temperatures.

The relationship between GMR and applied magnetic field strength is not linear but rather exhibits a characteristic sigmoidal curve. At low magnetic field strengths, the change in resistance is gradual. As the magnetic field strength increases, the change in resistance accelerates until it reaches a saturation point. Beyond this point, further increases in magnetic field strength produce minimal additional change in resistance. The exact shape of the curve depends on the specific GMR structure’s materials and dimensions.

This characteristic curve is crucial for sensor design and calibration. The sensitivity of the GMR sensor is often defined by the slope of the curve within a particular operating range. Understanding this relationship is vital to optimize the sensor’s performance for a specific application, as the sensitivity and dynamic range need to be appropriate for the expected range of magnetic field variations.

Fabrication of a GMR sensor involves sophisticated thin-film deposition techniques, often carried out under ultra-high vacuum conditions. The process typically consists of the following steps:

1. Substrate Preparation: A smooth and clean substrate, such as silicon wafer, is prepared.
2. Layer Deposition: Multiple thin layers of ferromagnetic (e.g., CoFe) and non-magnetic (e.g., Cu) materials are deposited using techniques like sputtering or molecular beam epitaxy. The precise control of layer thickness is critical to achieve optimal GMR.
3. Lithography and Etching: Photolithography and etching techniques are employed to define the desired sensor geometry and pattern.
4. Contact Formation: Metal contacts are formed to allow electrical measurements.
5. Packaging: The sensor is packaged to protect it from environmental factors and provide mechanical stability.

The entire process requires highly specialized equipment and expertise. Cleanroom facilities are essential to prevent contamination which can significantly affect the sensor’s performance. Quality control at each step is paramount to ensure the reliable fabrication of high-performance GMR sensors.

Manufacturing GMR devices presents several challenges:

• Precise Layer Control: The precise control of layer thickness and composition is crucial for achieving high GMR values. Even small deviations can significantly degrade performance.
• Uniformity: Maintaining uniformity across a large area is challenging, especially for large-scale production. Non-uniformity leads to variations in sensor response and performance inconsistencies.
• Defect Control: Defects in the thin films can significantly impact the GMR effect, leading to reduced sensitivity and reliability. Minimizing defects requires precise control of the deposition process and careful materials selection.
• Cost: The fabrication process involves sophisticated equipment and skilled labor, which can lead to relatively high manufacturing costs compared to other sensor technologies.
• Temperature Dependence: As mentioned earlier, the temperature sensitivity of GMR is a significant challenge which requires mitigation strategies during the design phase.

Overcoming these challenges requires continuous advancements in materials science, thin-film deposition techniques, and manufacturing processes. Research into new materials and fabrication methods is ongoing to improve the performance, reliability, and cost-effectiveness of GMR devices.

Spin-dependent scattering is the fundamental physical mechanism underlying the GMR effect. Electrons possess an intrinsic angular momentum called ‘spin,’ which can be either ‘up’ or ‘down’. In a GMR structure, consisting of alternating ferromagnetic and non-magnetic layers, the electrons experience different scattering probabilities depending on their spin orientation.

Imagine two lanes of traffic (spin up and spin down). If the lanes are aligned (ferromagnetic layers magnetized parallel), traffic flows smoothly (low resistance). However, if the lanes are misaligned (antiparallel magnetization), there’s congestion in one lane while the other is relatively clear (high resistance). This difference in scattering is the origin of GMR.

Specifically: In parallel alignment, electrons with both spin orientations can traverse the structure easily leading to low resistance. In antiparallel alignment, one spin orientation faces strong scattering at the ferromagnetic/non-magnetic interfaces, while the other experiences relatively less scattering. This difference in scattering probabilities leads to a significant change in the overall resistance of the structure, constituting the GMR effect.

Giant Magnetoresistance (GMR) technology, while revolutionary, isn’t without its limitations. One key challenge is its sensitivity to temperature variations. Changes in temperature can significantly affect the resistance of the GMR sensor, leading to inaccurate readings. This necessitates careful temperature compensation techniques, often involving sophisticated circuitry. Another limitation is its relatively low resistance compared to other sensor technologies. This can lead to higher noise levels and lower signal-to-noise ratios, especially in low-field applications. Furthermore, GMR sensors generally exhibit a limited linear range, meaning they perform optimally within a specific magnetic field strength range. Outside this range, the response becomes non-linear, impacting the accuracy and reliability of measurements. Finally, the manufacturing process of GMR sensors can be complex and expensive, limiting their widespread adoption in cost-sensitive applications.

GMR materials are primarily categorized based on their structure and the type of magnetic layers used. The most common are:

• Spin-Valve GMR: This type consists of a ferromagnetic layer with pinned magnetization (a fixed magnetic orientation), a non-magnetic conducting spacer layer (often copper or a similar material), and a free ferromagnetic layer whose magnetization can be easily rotated by an external magnetic field. The change in resistance depends on the relative orientation of the magnetizations in the two ferromagnetic layers. They offer high sensitivity and relatively good linearity.
• Current-Perpendicular-to-Plane (CPP) GMR: In CPP-GMR, the current flows perpendicular to the layers, unlike spin valves where it’s parallel. This configuration results in significantly larger magnetoresistance ratios compared to CIP (current-in-plane) structures, but it’s more challenging to fabricate.
• Tunnel Magnetoresistance (TMR): While technically distinct from GMR, TMR devices share similar operational principles. They utilize a thin insulating barrier between two ferromagnetic layers. Electron tunneling across this barrier is highly sensitive to the relative magnetization of the ferromagnetic layers, leading to a change in resistance. TMR devices generally exhibit higher magnetoresistance ratios than GMR devices, and they are increasingly preferred for many applications due to their improved sensitivity and better stability.

The properties of GMR materials, such as magnetoresistance ratio (the percentage change in resistance), sensitivity, linearity, and temperature coefficient, depend heavily on factors like layer thicknesses, material composition, and manufacturing techniques. For example, the choice of spacer layer material significantly impacts the overall performance. A thinner spacer layer can lead to stronger spin-dependent scattering and thus higher magnetoresistance, but it might also increase noise.

The future of GMR technology is bright, fueled by ongoing research and development. Several key trends are shaping this field:

• Improved Materials and Fabrication Techniques: Research is focused on exploring new materials and developing advanced fabrication techniques to enhance the magnetoresistance ratio, improve temperature stability, and reduce manufacturing costs. This includes exploring new magnetic materials with enhanced spin polarization and developing more efficient patterning techniques.
• Integration with Other Technologies: GMR sensors are being integrated with other technologies like microelectromechanical systems (MEMS) to create more sophisticated and multifunctional devices. Imagine a smart sensor that combines GMR with temperature or pressure sensors for more complete environmental sensing.
• Miniaturization and Enhanced Performance: The drive towards miniaturization continues, enabling GMR sensors to be incorporated into even smaller and more portable devices. This necessitates the development of new fabrication methods like nano-imprint lithography or self-assembly.
• Application-Specific Designs: Research is shifting toward developing GMR sensors tailored for specific applications, optimizing their design and characteristics to meet the unique requirements of each industry, like optimized sensors for high-temperature environments or for detecting extremely weak magnetic fields.

These advancements promise even more sensitive, reliable, and cost-effective GMR-based devices with a wider range of applications.

The sensitivity of a GMR sensor is typically expressed as the change in resistance (ΔR) per unit change in magnetic field (ΔH). It’s often quantified as ΔR/R per Oe (oersted) or ΔR/R per mT (millitesla), where R is the initial resistance. Higher values indicate a more sensitive sensor. To measure the sensitivity, a known magnetic field is applied to the sensor, and the resulting change in resistance is meticulously measured using a precise Wheatstone bridge or similar circuitry. This measurement is then repeated for different magnetic field strengths to determine the sensitivity across the sensor’s operational range. Calibration with a highly accurate magnetometer is crucial to obtain reliable sensitivity results.

For example, a high-sensitivity GMR sensor might exhibit a ΔR/R of 1% per 1 Oe, indicating that a 1 Oe change in magnetic field will cause a 1% change in the sensor’s resistance. This is usually determined experimentally, through a process of systematic change in field strength and subsequent resistance measurement. Furthermore, sophisticated software is frequently used to analyze the data, account for background noise, and provide accurate sensitivity figures.

Noise significantly impacts GMR measurements by masking the subtle changes in resistance caused by the magnetic field. Different types of noise affect GMR sensors:

• Thermal Noise: Random fluctuations in electron motion due to temperature produce a voltage fluctuation across the sensor, which is proportional to the square root of temperature.
• Johnson-Nyquist Noise: This intrinsic noise is present in all resistive elements and is directly related to the sensor’s resistance and temperature. Reducing the resistance of the sensor can decrease this noise.
• Flicker (1/f) Noise: This low-frequency noise is difficult to predict and model, but it is highly dependent on the manufacturing process and material imperfections.
• Magnetic Noise: External magnetic fields that are not part of the intended measurement can introduce significant noise. Shielding the sensor from these sources is important.

These noise sources can degrade the signal-to-noise ratio, making it difficult to accurately determine the change in resistance due to the target magnetic field. To mitigate the effects of noise, various techniques are employed, such as signal averaging, filtering, and using low-noise amplifiers. Careful sensor design and shielding are also crucial in minimizing noise pickup.

Several techniques are used for characterizing GMR, each offering specific insights into its properties:

• Magnetoresistance Measurement: This is the most fundamental characterization technique, involving applying a varying magnetic field to the sensor and measuring the resulting change in resistance. This helps determine the magnetoresistance ratio, sensitivity, and linearity.
• X-ray Diffraction (XRD): XRD is used to analyze the crystal structure and layer thicknesses of the GMR multilayer. This ensures the quality and consistency of the GMR stack and gives information on its structural properties.
• Transmission Electron Microscopy (TEM): TEM provides high-resolution images of the GMR layers, allowing for the observation of defects and interfaces. This is crucial for understanding the microstructural features that influence the magnetoresistance.
• Magneto-Optical Kerr Effect (MOKE): MOKE is a non-contact technique used to measure the magnetization of the ferromagnetic layers in the GMR structure as a function of the applied magnetic field. This helps understand the magnetic behavior of each layer and can uncover any unexpected interactions between layers.
• Electrical Characterization: This involves measuring other electrical parameters like the sensor’s resistance, impedance, and noise levels to assess its overall performance. Various techniques are used, from standard four-point probes to high-frequency network analyzers.

Combining these techniques provides a comprehensive understanding of the GMR sensor’s structural, magnetic, and electrical properties, which are vital for optimizing its performance and reliability.

Spin polarization is a fundamental concept in understanding GMR. Electrons possess an intrinsic angular momentum called spin, which can be either up or down. In ferromagnetic materials, the electrons’ spins are preferentially aligned, leading to a net magnetization. Spin polarization refers to the difference in the density of electrons with spin up versus spin down at the Fermi level (the highest occupied energy level in a material at absolute zero). A higher degree of spin polarization means a larger imbalance between spin-up and spin-down electrons.

In a GMR structure, the spin polarization of the ferromagnetic layers plays a crucial role. When the magnetizations of the two ferromagnetic layers are parallel, the spin-polarized electrons can easily pass through the non-magnetic spacer layer, resulting in lower resistance. Conversely, when the magnetizations are antiparallel, the spin-polarized electrons experience stronger scattering in the spacer layer, leading to higher resistance. The magnitude of the change in resistance (the magnetoresistance effect) is directly related to the degree of spin polarization in the ferromagnetic layers.

Think of it like this: imagine a highway with two lanes, one for spin-up and one for spin-down electrons. In a ferromagnet, one lane is much more crowded (higher spin polarization). When the lanes are aligned, traffic flows smoothly. When misaligned, there’s a traffic jam (higher resistance).

The thickness of the ferromagnetic and non-magnetic layers in a Giant Magnetoresistance (GMR) multilayer structure critically influences the GMR ratio. Think of it like this: the spin-dependent scattering of electrons, which is the heart of the GMR effect, needs to be carefully managed.

If the ferromagnetic layers are too thick, the spin polarization at the interfaces (where the magic happens) is reduced, decreasing the GMR. Conversely, if they’re too thin, the layers become discontinuous or exhibit other structural defects, again harming the GMR. The non-magnetic spacer layer thickness also matters: it needs to be optimized to allow for sufficient spin-dependent scattering, yet prevent the ferromagnetic layers from interacting directly (which would negate the effect). Typically, an optimal spacer layer thickness exists where the GMR is maximized. Experimentally, we’ve found that slight deviations from the optimal thickness (say, a few Angstroms) can significantly impact the observed GMR ratio.

A good analogy is a water slide: the ferromagnetic layers are like the twists and turns, affecting the direction of the water (electrons). The spacer layer is like a straight stretch between the turns. Too many turns (thick ferromagnetic layers) or too little space between them (thin spacer layer) reduces the overall difference in the water flow (GMR).

Improving the GMR ratio involves optimizing several aspects of the multilayer structure and fabrication process. Key methods include:

• Material Selection: Choosing ferromagnetic materials with high spin polarization (like CoFe or Co) and non-magnetic spacers with strong spin-dependent scattering (like Cu or Au) significantly enhances the GMR. For instance, using highly ordered alloys reduces scattering events that oppose the GMR effect.
• Layer Thickness Optimization: As discussed earlier, meticulous control over layer thicknesses is paramount. This often involves techniques like sputtering or molecular beam epitaxy (MBE) with precise control over deposition rates and layer growth.
• Interface Engineering: Sharp and clean interfaces are crucial. Techniques like inserting buffer layers or employing specific deposition methods (e.g., low-energy ion bombardment) can help minimize interfacial roughness and alloying, which can degrade the GMR.
• Annealing: Controlled heat treatments can improve the crystal structure and reduce defects, leading to an increased GMR. However, excessive annealing can lead to interdiffusion of the layers, thus it requires careful parameter optimization.
• Multilayer Design: Incorporating multiple GMR layers in a stacked configuration or designing more complex structures (such as spin valves or magnetic tunnel junctions) can amplify the GMR significantly.

Defects in GMR structures drastically affect their properties. These defects can range from microscopic imperfections (like point defects, dislocations, or grain boundaries) to macroscopic issues (such as cracks or delamination). Imagine trying to build a precise clock with wonky gears – it simply won’t work correctly.

Point defects, for example, scatter electrons randomly, reducing the spin-dependent scattering that produces GMR. Grain boundaries can disrupt the coherent spin transport across the layers. Interdiffusion between the ferromagnetic and non-magnetic layers also severely diminishes the effect because the distinct layers essential for spin-dependent scattering are blurred. Macroscopic defects, such as cracks, create conductive paths that bypass the GMR mechanism. Therefore, meticulous fabrication methods aiming for high-quality, defect-free structures are crucial to achieve high GMR ratios.

GMR devices are integrated into systems primarily as sensors. Their sensitivity to magnetic fields makes them perfect for applications like:

• Hard disk read heads: GMR read heads are the cornerstone of modern hard disk drives, enabling high-density data storage. They exploit the change in resistance as the magnetic bits pass by the read head to detect the stored data.
• Magnetic field sensors: GMR sensors are used in various applications requiring precise magnetic field detection, such as automotive sensors (e.g., for speed control, anti-lock braking systems), navigation systems, and current sensors.
• Biomedical sensors: The biocompatibility of some GMR materials allows their use in creating biosensors. They can detect tiny magnetic labels used in magnetic resonance imaging (MRI) or track specific biological processes.

Integration involves fabricating the GMR elements using techniques like thin-film deposition, followed by lithographic patterning to create the desired sensor structures. These structures are then incorporated onto circuit boards using standard microelectronic packaging techniques.

Both GMR and Tunnel Magnetoresistance (TMR) are magnetoresistive effects used in sensor applications, but they differ significantly in their mechanism. GMR relies on the spin-dependent scattering of electrons in a multilayer structure where the electrons travel through the layers. TMR, on the other hand, utilizes electron tunneling through a thin insulating barrier separating two ferromagnetic layers.

TMR generally exhibits larger magnetoresistance ratios than GMR, making it advantageous for high-sensitivity applications. However, GMR offers better noise performance and can tolerate some degree of interfacial imperfections. The choice between GMR and TMR often depends on the specific application requirements; for high-density storage, TMR is preferred, while GMR might be advantageous for applications that benefit from better noise tolerance.

During a project involving the fabrication of GMR-based magnetic field sensors, we encountered unusually low GMR ratios. Initial investigation pointed to potential defects in the multilayer structure. After systematically analyzing the fabrication process, we realized that subtle variations in the sputtering conditions (specifically the argon pressure) had affected the quality of the interfaces between the ferromagnetic and non-magnetic layers.

We addressed this issue by meticulously optimizing the sputtering parameters while monitoring the film quality using in-situ techniques. Through careful adjustments, we were able to obtain high-quality GMR structures with ratios matching the expected values. This troubleshooting experience highlighted the importance of precise process control in GMR device fabrication and the effectiveness of in-situ monitoring techniques in diagnosing and correcting such problems.

At the heart of the GMR effect lies the spin-dependent scattering of conduction electrons. In a typical GMR structure, two ferromagnetic layers are separated by a non-magnetic spacer layer. When the magnetizations of the ferromagnetic layers are aligned parallel, the resistance is lower. This is because spin-up electrons experience reduced scattering in both layers, leading to higher conductance.

When the magnetizations are anti-parallel, however, spin-up electrons experience strong scattering in one layer and spin-down electrons in the other. This results in increased overall resistance. This difference in resistance between the parallel and anti-parallel magnetization states constitutes the GMR effect. It’s a quantum mechanical phenomenon, relying on the fact that electrons possess both charge and spin, with the spin’s interaction with the material’s magnetic structure determining their scattering behavior.