This is topical for Battlescape because it's a real-world shield concept. It's not an energy field, but plasma controlled by a magnetic field. It would also look pretty cool.
The Magnetoshell deploys a simple dipole magnetic field containing a magnetized plasma. It is interaction of the atmosphere with this magnetized plasma that supplies a significant impediment to atmospheric flow past the spacecraft, and thereby producing the desired drag for braking. Frictional heating would no longer be of concern as the energy dissipation required to slow the spacecraft would be deposited into the plasma ions helping to maintain the Magnetoshell plasma while at the same time shielding the spacecraft itself from frictional heating. With the aeroshell now being composed of massless magnetic field, the transverse scale of the magnetic barrier can be as large as 100 meters while requiring no more than a gram of plasma.
Note that while the field is massless, the magnets are certainly not.
In Phase I a full system was designed for Neptune and Mars missions. This analysis showed that a 200 kg, 2 m magnet could generate a 9 m radius Magnetoshell for Neptune aerocapture with a 21 km/s injection at a peak force of 150 N entirely removing the need for a TPS. At Mars, a 2.5 m magnet could generate a 21 meter radius Magnetoshell, providing aerocapture for a 60 metric ton payload removing the dedicated aerocapture TPS and saving $2 B for DRA 5.0.
(DRA 5.0 is the latest (2009) iteration of the Mars Design Reference Architecture)
So the Mars magnetic shield is a roughly 250kg magnet plus whatever is needed to power it and possibly cool it. The article makes no mention of magnetic field strengths, but I saw speculation that a 0.5 to 1.0T magnetic field would be reasonable. By way of comparison, MRIs use 1.5 to 7T magnetic fields, and even small neodymium magnets produce 0.2T fields. 1T is a very powerful magnetic field.
The current ablative thermal protection material of choice is PICA. SpaceX uses PICA-X, which has a density of 0.25g/cm^3. On Dragon, the coating is 750mm thick, resulting in a mass of around 800kg. 125mm burns off during reentry, suggesting the potential for reuse.
The respective masses suggest that the magnetic system could be an effective one for reentry. However, the nice thing about PICA is that you don't have to turn it on or power it up. In contrast, if the magnet is an electromagnet, then such a system represents at least one more mode of failure for a spacecraft. Certainly the plasma generators/emitters represent additional complexity.