Does stacking a magnet make it stronger?

It's a common question that arises when handling powerful magnets: If one is good, are two stacked together twice as good? The intuitive answer might be "yes," but in the world of physics and material science, the effect of stacking magnets is more complex than simple addition.

The answer, in short, is that stacking two identical magnets aligned pole-to-pole will make the resulting assembly stronger, but not necessarily twice as strong. The increase in strength is significant, yet highly dependent on the design, size, and proximity to the target surface.

1. Why Stacking Increases Strength

When you stack two identical magnets with the North pole of one touching the South pole of the other (N-S stacking), you effectively create a single, larger magnet.

Increased Length (Magnetic Axis): The most crucial factor is that stacking increases the length or thickness of the magnet along the axis of magnetization.

The Benefit: A thicker magnet has a longer magnetic path. This longer path is significantly better at resisting its own self-demagnetizing forces, meaning more of the internal magnetic energy is projected outward into the external field.

Greater Field Projection: Because the magnetic field lines have a longer distance to travel internally, the combined magnet can project a stronger field further away from its pole faces. The resulting field strength at a distance will be much greater than that of a single, thin magnet.

2. Why It's Not Exactly Double the Strength

While the resulting field is stronger, the increase is not a linear 1+1=2 formula for several reasons:

Non-Linearity of Magnetic Fields: Magnetic forces decrease rapidly as distance increases (following an inverse square or inverse cubic law, depending on the measurement). The increase in strength from stacking is significant at a distance, but the improvement is less pronounced when measured right at the surface.

The Pull Force Measurement: If you measure the pull force (the maximum weight the magnet can lift when touching a steel plate), the stacked magnet will have a higher pull force, but it won't be double. This is because the original single magnet was likely already near the saturation point for that surface area.

The Effect of the Gap: Even if the magnets are perfectly touching, there is always a tiny air gap between the two surfaces. This minute break slightly reduces the efficiency of the magnetic circuit compared to a single, monolithic magnet of the same total thickness.

For example, stacking two one-inch thick magnets might result in a magnet assembly that is 1.5 to 1.7 times stronger than the single magnet, not 2 times stronger.

3. Stacking vs. Scaling Up

If your goal is maximum strength, you should always compare stacking to purchasing a single, monolithic magnet of the same total dimensions.

The Single Magnet Advantage: A single magnet that is 2 inches thick (the total thickness of two 1-inch stacked magnets) will always be slightly stronger than two 1-inch magnets stacked together. This is because the single magnet has no internal air gap, making the magnetic circuit more efficient.

Therefore, stacking is an excellent way to boost the power of existing magnets, but if you are designing a product from scratch, purchasing a single, thicker unit is the most efficient choice for pure strength.

4. Stacking for Design Flexibility

Despite the slight loss of efficiency compared to a monolithic magnet, stacking offers valuable advantages:

Cost-Effectiveness: It may be cheaper or faster to obtain two standard-sized magnets than one custom-sized, extra-thick magnet.

Thermal Management: In high-power applications, using multiple smaller magnets separated by a material allows for better heat dissipation than one large magnet.

Controllable Force: Stacking allows users to easily add or subtract units to fine-tune the required magnetic force without changing the entire assembly.

In conclusion, stacking two identical magnets (N-S) absolutely makes the combined assembly stronger by increasing its thickness and improving field projection, especially over a distance. While the resulting force is not a perfect doubling, it is a highly effective and practical way to enhance the strength of your magnetic application.