Taking apart MAMR: Why hasn't this technology taken over the HDD world yet?
1. What is MAMR?
MAMR (Microwave-Assisted Magnetic Recording) is a technology for recording data on hard drives (HDDs), where microwaves help to remagnetize tiny bits, allowing you to increase storage density without loss of reliability.
How does it work?
- The Spin Torque Oscillator (STO) is integrated into the recording head — mini microwave generator.
- Before recording, the STO emits a high-frequency field (~20-40 GHz), which "rocks" the magnetic moments of the bits, temporarily reducing their stability.
- Now even the weak field of the head is enough for remagnetization.
- After recording, the microwaves turn off — the bits become stable again.
Analog:
Imagine that a bat is a door with tight hinges. Without MAMR, it cannot be opened with a weak push. With MAMR, the door is first "rocked" (by microwaves), and then easily opened.
2. Why is MAMR a breakthrough?
- Recording density ↑: You can reduce the bits without the risk that they will "demagnetize" from temperature.
- Reliability: There is no extreme heat (as in HAMR), which means that the disc will last longer.
- Energy efficiency: No need for a giant magnetic field.
3. Why isn't MAMR dominating yet?
🔹 Reason 1: HAMR turned out to be faster
- The competing HAMR (Heat-Assisted Magnetic Recording) technology uses laser heating for recording.
- Seagate released the most spacious hard drive in history - https://www.techradar.com/pro/seagate-confirms-40tb-hard-drives-have-already-been-shipped-but-dont-expect-them-to-go-on-sale-till-2026
🔹 Reason 2: The complexity of STO production
- Spin Torque Oscillator (STO) is a nanodevice that must:
— Generate an accurate frequency (otherwise the recording will not work).
- Be small enough (so as not to interfere with the operation of the head).
- So far, Toshiba is the only company that has been able to establish mass production.
🔹 Reason 5: Industry conservatism
HDD manufacturers have been investing in PMR/CMR (traditional technologies) for decades.
- The transition to MAMR requires the restructuring of production lines — it is expensive and risky.
It is quite possible that none of the technologies will be the clear winner. "I have not yet been able to talk to any specific customer who will exclusively use only HDD with one of the technologies," says Mark Ginen, founder of the consortium of Advanced storage Technologies. "I think there will be companies in the market that will buy both."
4. Does MAMR have a future?
- Yes, but in niche scenarios:
-
Where reliability is important: Archives, medical data, backups.
- Where record volumes are not needed: Enterprise systems with a balance of price and capacity.
- Toshiba plans to increase the MAMR density to 30+TB by 2026.
5. Comparison of MAMR and HAMR
| Parameter | MAMR (Toshiba) | HAMR (Seagate/WD) |
|---|---|---|
| Technology | Microwaves (STO) | Laser + Magnetic field |
| Max. capacity | 22TB (2024) | 24+ TB (2024) |
| Risks | Complexity of STO | Overheating, disk degradation |
| Price | Cheaper than HAMR | More expensive because of lasers |
6. Conclusion
MAMR is an elegant solution, but for now:
- HAMR is inferior in the "terabyte race".
- Depends on Toshiba's progress in miniaturization of STO.
- Chance of Success: If HAMR runs into reliability issues, MAMR will be the HDD's savior.
How It Works? Let's dig a little deeper.
Simplified explanation of MAMR operation
Imagine that a hard disk is a notebook where data is written with tiny magnetic arrows (↑ and ↓). The smaller the arrows, the more information will fit, but there is a problem.:
Problem
If the arrows are made very small, it is difficult to turn them over. You need a strong magnet (like a powerful refrigerator magnet), but the HDD head is a weak button magnet.
Solution: MAMR (microwave "help")
A "microwave for atoms" — Spin Torque Oscillator (STO) has been added to the recording head. That's how it works.:
1. STO is a "sandwich" of two magnetic layers
- The first layer: As a "teacher" who arranges the electrons (makes their spins the same).
- The second layer: As a "rebellious student" — his electrons are set up in the opposite way.
When current is passed through them:
- Electrons from the first layer collide with the second.
- The "stubborn" electrons of the second layer ** begin to oscillate** (like a swing if they are slightly pushed to the beat).
- These vibrations generate microwaves (like Wi-Fi, but very spot-on).
2. How do microwaves help record data?
- The microwaves are tuned to the resonant frequency of the magnetic grains of the disk (like a tuning fork that makes only one glass vibrate).
- They rock the magnetic arrows on the disk, making them "malleable".
- Now even the weak field of the head is enough to flip the arrow (write 0 or 1).
- After recording, the microwaves turn off — the arrows "freeze" again and store the data.
3. Why does it feel like "heating up", but without the temperature?
- Ordinary heating (as in HAMR) is like setting fire to paper to write on it. It's dangerous!
- MAMR is like shaking a piece of paper to make the ink fit more easily. Without fire!
And now — a super simple analogy
Imagine that:
- Data is nails driven into a board.
- The usual entry — you are trying to drive a nail into an oak plank ** with a small hammer**. It doesn't work!
- MAMR — you first "vibrate" the board (with microwaves), and now even a weak hammer blow drives a nail.
Why is it brilliant?
- No destruction: No overheating (as in HAMR), the disk lives longer.
- Accuracy: Microwaves work only where needed, without touching neighboring data.
- Energy Saving: No need for giant magnets or lasers.
Output:
MAMR is a ** "smart vibration"** that allows HDD to break records in terms of capacity without violating the laws of physics. The technology is not perfect yet, but it has every chance of changing the future of hard drives!
HDD recording head device with MAMR
The picture shows an enlarged section of the tip of the recording head of a hard disk (HDD) using Microwave-Assisted Magnetic Recording (MAMR) technology. Let's look at each element and its role in recording data.
1. The main components in the image are
A. Write Head
This is the part of the head that remagnetizes the bits on the disk, writing data (0 or 1).
B. The Reading Head
Responsible for reading data from the disk (determines the direction of the magnetization of the bits).
C. Microwaves
Indicated by arrows is the high frequency magnetic field generated by the Spin Torque Oscillator (STO).
2. Detailed structure of the recording head
① FGL (Field Generation Layer)
- This is the part of the STO (Spin Torque Oscillator) that generates the microwave field.
- Consists of magnetic material, the vibrations of which create a high-frequency (~20-40 GHz) field.
② SIL (Shielded Interaction Layer)
- A layer that focuses microwave radiation into the desired recording area.
- Prevents the field from scattering so as not to affect neighboring bits.
③ STO (Spin Torque Oscillator)
- The "heart" of MAMR is a microscopic microwave generator.
- Consists of:
- FGL (generates a field),
- Disconnected layers (enhance the effect).
- Powered by spin-polarized current (electrons "spin up" magnetic moments, creating vibrations).
④ Multimagnetic Pole
- The main part of the recording head, which creates a permanent magnetic field for remagnetization of bits.
- In combination with microwaves from STO, it allows you to record data on ultra-small bits.
⑤ Non-magnetic layer
- Separates magnetic components, preventing unwanted interactions.
- Usually from ruthenium (Ru) or similar materials.
3. How does it work together?
- Recording begins:
- Current is applied through the STO → FGL generates microwaves.
-
Microwaves affect the bit:
- They ** sway the magnetic moments** in the bit, reducing their stability.
- The head remagnetizes the bit:
- The multi-magnetic pole creates a weak field, which is now sufficient to switch the bit (↑ or ↓).
- Recording completed:
- The microwaves turn off → the bit ** becomes stable again**.
4. Why is this a breakthrough?
- Previously, ** a huge field was required to write to small bits (it cannot be created in a miniature head).
- With MAMR microwaves temporarily reduce the resistance bits → recording is possible even with a weak field.
Analog:
Imagine that a bat is a door with tight hinges.
- Without MAMR: You're trying to open it with your bare hands (not strong enough).
- With MAMR: First the door is "rocked" (microwaves), then you open it easily.
5. Comparison with a regular head
| Component | Regular Head | Head with MAMR |
|---|---|---|
| Recording | Magnetic field only | Magnetic field + microwaves |
| Density | Limited (~1 Tbit/in2) | Higher (~2+ Tbit/in2) |
| Reliability | Stable | Stable + protection against superparamagnetism |
6. The future of technology
- Toshiba already uses MAMR in disks MG09 (18 TB) and MG10 (22 TB).
- Goal: to achieve 4 Tbit/in2 (disks on 30+ TB).
Problems:
- Fine-tune the STO (so that the microwaves do not interfere with neighboring bits).
- Competition with HAMR (where laser heating is used).
Relationship between STO resistance and applied magnetic field
*1. The general structure of the STO *
The STO consists of three key layers:
- FGL (Free Gadget Layer)
-
A "free" magnetic layer that can change the magnetization.
- Analog: a piece of paper that can be turned over.
-
Non-magnetic layer
is a non-magnetic material (for example, copper).- Analog: the air gap between two magnets.
SIL (Spin Injection Layer)
-
A fixed magnetic layer with constant magnetization.
- Analog: a magnet glued to a table.
2. How are microwaves generated?
Step 1: Apply current
- High-density electric current is passed through the STO layers (see values in the diagram: from (8.7 \times 10^6) to (1.4 \times 10^8) A/cm2).
- What happens:
- The electrons in the current "twist" (polarize) when passing through the SIL.
- These polarized electrons are "injected" into FGL.
Step 2: Excitation of vibrations
- In FGL, the electron spins begin to precess (like a spinning top about to fall).
- This creates an alternating magnetic field (microwaves) at a frequency of ~15-20 GHz.
Step 3: Resonance with the disc
- The microwaves synchronize with the magnetic grains on the disk, reducing their coercivity.
3. Key parameters from the scheme
Current density (A/cm2)
- The higher the current density, the stronger the fluctuations:
-(8.7 \times 10^6) — the threshold for the start of generation.
- (1.4\times 10^8) — maximum efficiency.
STO States
- Oscillating state (Fluctuations):
-
FGL is actively oscillating → microwaves are generated.
- The arrow (direction of magnetization) rotates rapidly.
-
Non-oscillating state (Rest):
- FGL is static → there are no microwaves.
- The arrow is fixed.
Why do we need an intermediate (non-magnetic) layer in STO?
Intermediate layer in Spin Torque Oscillator (STO) — this is a critical element, without which the generation of microwaves would be impossible. That's why it's needed and how it works.:
1. The role of the intermediate layer
This layer (usually made of copper, aluminum, or magnesium oxide) performs two key functions:
🔹 (1) Separates two magnetic layers (FGL and SIL)
- FGL (Free Gadget Layer) is a "free" layer that can fluctuate.
- SIL (Spin Injection Layer) is a "fixed" layer with constant magnetization.
Without an intermediate layer:
- The magnetic layers ** would stick together** (like two magnets), and FGL would not be able to oscillate.
- There would be no spin-polarized current — basics of STO operation.
🔹 (2) Allows the current to "transfer" spin information
- When electrons pass through SIL, their spins are polarized (aligned in the same direction).
- Then they ** pass through a non-magnetic layer**, maintaining their polarization.
- Reaching FGL, these electrons transfer their spin moment to it, causing it to oscillate.
2. Why is it a non-magnetic material?
- The magnetic material would shield the spin current → the FGL oscillations would stop.
- Dielectric (for example, MgO) It is sometimes used to enhance the spin transfer effect.
Optimal thickness: ~1-3 nm.
- Too thin → the layers will "stick together".
- Too thick → the electrons will lose their polarization.
3. What would happen without this layer?
- It would be impossible to control FGL — it would just "stick" to SIL.
- ** There would be no microwaves** — there would be no fluctuations.
- MAMR would not work — recording to high-density discs would remain impossible.
Graph analysis: Comparison of SNR of conventional and MAMR heads
This graph demonstrates the key advantage of MAMR (Microwave-Assisted Magnetic Recording) Before traditional magnetic recording: increased signal-to-noise ratio (SNR) by 7 dB. Let's take it apart piece by piece.
1. X-axis and Y-axis: what is depicted?
- X-axis (Down-track / Cross-track direction, nm)
-
Shows the spatial position of the head relative to the track on the disc.
- Down-track — along the track (the direction of movement of the data).
- Cross-track — across the track (recording width).
Y-axis (SNR, dB / Magnetization, %)
-
SNR (Signal-to—Noise Ratio) is the ratio of the useful signal to noise (the higher the better).
- Magnetization saturation — the level of magnetization (↑ up / ↓ down).
2. Comparison of conventional and MAMR heads
(A) Conventional R/W Head
- SNR: Low (conventionally ~0 dB on the graph).
-
Problem:
- At high recording density, the magnetic bits become too small → the signal weakens, the noise increases.
- The head cannot clearly remagnetize tiny areas → the data is distorted.
(B) MAMR head
- SNR: Higher by 7 dB (significant improvement!).
- Reason:
- Microwaves from STO (Spin Torque Oscillator) helps ** to re-magnetize the bits more clearly**.
- This reduces the "smearing" of the signal and suppresses noise.
3. How do microwaves improve SNR?
- Accurate recording
-
Microwaves ** locally reduce the coercivity** (Coercivity is the resistance of a ferromagnet to demagnetization) of the disc material.
- The head can record smaller and clearer bits without errors.
-
Improved reading
- Because the bits are recorded more clearly, it is easier for the head to recognize them - > less noise.
Stability
MAMR does not overheat the disc (unlike HAMR), so there is no additional thermal noise.
4. Why is +7 dB important?
- Increase in SNR by 3 dB = doubling of information capacity.
- +7 dB ≈ 5 times better signal-to-noise ratio → You can increase the recording density without data loss.
Example:
If a conventional head worked with a density of 1 Tbit/in2, then MAMR allows you to rise to 1.5–2 Tbit/in2 with the same reliability.
5. Conclusion
- MAMR doesn't just "slightly improve" the recording — it makes it better.
- +7 dB SNR means that HDDs with MAMR will be able to:
- store more data,
- read it faster,
- work longer without errors.
Results of evaluation of overwrite performance of MAMR read and write heads
This Fihure shows the changes in
overwrite performance over a range of write current (Iw). It
indicates that, when the STO is on, MAMR provides a roughly 10 dB
higher overwrite performance than a conventional magnetic
recording method without an STO. This
result indicates that the microwave field emitted by an STO helps
to achieve good write performance, demonstrating the feasibility
of MAMR. As a result of the foregoing, MAMR is considered to be
a promising next-generation high-density HDD recording
technology capable of overcoming the trilemma associated with
high-Ku recording media
Evaluation of a prototype HDD with MAMR read/write heads
and media
*Results of long-term reliability tests of prototype
MAMR HDDs
Figure 5 compares the changes in the bit error rate
(BER) of the MAMR and conventional HDDs over time. The MAMR media were made of materials similar to those used for conventional
recording media. Figure 5 presents the results obtained at a
recording density close to the maximum recording density of the
existing HDDs. It shows that MAMR with an STO provides a
significant reduction in the BER.
Generally, an STO with higher drive current generates a microwave
field with higher intensity and thus provides higher energy-assistfor MAMR, resulting in a greater reduction in the BER. However,
excessive current could degrade reliability because of Joule
heating and electromigration within the STO. In the example
shown in Figure 5, the BER of MAMR remains unchanged for up
to 1,000 hours of write operations without any STO degradation,
the possibility of which had been a concern. From this evaluation,
we have also obtained information about adequate STO drive
conditions. (from the article)
Bottom line: MAMR is a smart way to extend the life of an HDD, but the technology is still fighting for a place in the market, let's see what happens next.
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