Degaussing

A strong magnetic field, a short pulse, and the data on a hard drive is gone: that is how degaussing is often described. It is not quite that simple. Whether a degausser really works depends on the data carrier and on the field strength of the device. On SSDs it does not work at all. This glossary entry explains how demagnetizing works, where it is used and where its limits lie.

What is degaussing?

Magnetic data carriers store information as tiny magnetized areas. Their alignment stands for zeros and ones. In degaussing, the data carrier is exposed to a magnetic field that is stronger than the force with which these areas hold their alignment. This force is called coercivity. If the field is strong enough, the order is lost and the stored data can no longer be read out.

The name goes back to the unit gauss, with which magnetic flux density is measured. "De-gauss" therefore means roughly "to demagnetize". A degausser is the device for it. There are designs with permanent magnets and others that generate a short, strong pulse with electromagnets.

How a degausser works

The data carrier is placed in a chamber or on a surface of the degausser. The device builds up a field that fully penetrates the data carrier. Two values are decisive:

• Field strength of the degausser: It must be well above the coercivity of the data carrier. Manufacturers state it in oersted or gauss.
• Coercivity of the data carrier: Modern hard drives and tapes store very densely. To do so, they use materials that hold their magnetization particularly firmly. An older or weak degausser may not be sufficient for this.

On a hard drive, a sufficiently strong field destroys not only the user data but also the so-called servo tracks. These are factory-written markings with which the read head finds its position. Without them, the hard drive is no longer usable. The same applies to many modern magnetic tapes. In practice, degaussing is therefore usually a final stop: afterwards the data carrier can be neither resold nor reused.

Where degaussing is used

Data carrier	Storage principle	Does degaussing work?
HDD (hard drive)	magnetic	Yes, if the field strength matches the coercivity; the hard drive is generally unusable afterwards
Magnetic tape (e.g. LTO)	magnetic	Yes, if the field strength is sufficient; modern tapes place high demands
Floppy disks, magnetic stripe cards	magnetic	Yes, even with comparatively weak devices
SSD, USB stick, memory card	Flash memory (electrical)	No, the data remains
Hybrid hard drive (SSHD)	magnetic and flash	Only partially; the flash cache remains untouched
CD, DVD, Blu-ray	optical	No

Degaussing is used above all where large quantities of magnetic data carriers accumulate that are not to be reused, such as tape archives from data centers. Anyone who wants to reuse or sell a Magnetic tape (LTO) or a HDD needs, by contrast, an erasure method that leaves the data carrier functional.

Limits and risks

• No protection with flash memory: SSDs, USB sticks and memory cards store electrically. The magnetic field changes nothing about that. The US guideline NIST SP 800-88 cites exactly this case as an example: the process runs through without error, but no data is sanitized.
• Devices that are too weak: NIST SP 800-88 in Revision 2 of September 2025 points out that many existing degaussers do not have enough force for data carriers with high coercivity.
• Unusable but not erased: A field can damage the servo tracks and cripple the drive without securely removing all data on the platters. From the outside, both look the same.
• Hard to verify: After degaussing, a hard drive can usually no longer be addressed. A read-back test as a check is then hardly possible. What is mainly checked is whether the device worked correctly.
• No resale: The residual value of the data carrier is lost.

NIST SP 800-88 Rev. 2 counts degaussing among the physical Purge methods but explicitly states that at the time of publication it does not count as a recognized Destroy method. For details, the guideline refers to the IEEE 2883 standard and NSA requirements. Many security concepts therefore combine demagnetizing with subsequent physical destruction.

Example: tape archive and server hard drives from a data center

A simplified example shows what the decision can look like in practice. A company dissolves a server room. What remains are older magnetic tapes, servers with HDDs and servers with SSDs.

1. IT records all data carriers with serial number and type in a list and separates magnetic from flash storage.
2. Degaussing is ruled out for the SSDs. They are erased with software or, if that is not possible, destroyed physically.
3. The working HDDs are to be resold. They are erased with software so that they remain usable and an erasure certificate for each serial number is produced.
4. The old tapes are no longer needed. Here, demagnetizing with a suitable device followed by shredding, or destruction in accordance with DIN 66399 directly, come into question.

The example shows: it is not the data carrier itself that decides, but the combination of storage technology, desired reuse and proof. When erasing is cheaper than destroying is explained in our guide Hard drive destruction: costs and alternatives.

Degaussing in IT decommissioning and at Second IT

For the physical destruction of data carriers, the DIN 66399 standard is authoritative in Germany. It describes security levels for shredding, divided by material classes such as H for hard drives and T for magnetic data carriers such as tapes. Which level suits which data is explained in our guide DIN 66399: protection classes and security levels.

Second IT relies on two paths that clearly document the data carrier and its data: working HDDs, SSDs and mobile devices are erased with Blancco, with a digitally signed erasure certificate for each device. Data carriers that cannot be erased, such as defective media, are shredded in-house in accordance with DIN 66399 at security level H-5. The destruction is video-monitored and documented by serial number and certificate of destruction. More on this under in-house data carrier destruction.

Distinction from related terms

Degaussing is a physical method, but not shredding. A Hard drive shredder destroys the data carrier mechanically into particles of a defined size. Software-based overwriting and commands such as Secure Erase, by contrast, work through the drive’s interface and keep it functional. The umbrella term for all methods that remove data irretrievably is described in the entry Data Sanitization.

Frequently asked questions about degaussing

What does a degausser do?

A degausser generates a strong magnetic field that destroys the magnetic alignment on hard drives, tapes or floppy disks. If the field is strong enough for the data carrier, the stored data can no longer be read afterwards.

Can an SSD be demagnetized?

No. SSDs store data electrically in flash cells, not magnetically. A degausser has no effect on them. SSDs are sanitized with suitable erasure software or manufacturer erase commands, or destroyed physically.

Is a hard drive still usable after degaussing?

Generally not. The magnetic field also destroys the servo tracks that the read head needs for orientation. Afterwards the hard drive can usually be neither rewritten nor resold.

Is degaussing enough as proof for the GDPR?

The method itself is not proof. You need a report for each data carrier with serial number, device, date and result. Because demagnetized hard drives can hardly be tested any more, many companies combine degaussing with documented destruction.

When does it make sense to demagnetize a hard drive?

When large quantities of magnetic data carriers accumulate that are not to be reused, such as tape archives from data centers. If a data carrier is to be sold or reused, a method is needed that leaves it functional.