The dataset's ranked leader holds 165 records, noticeably ahead of the fifth-place assignee at 60 and the tenth at 23. The top five assignees combined account for 35.9% of all 1,291 records in scope, and the top ten reach 46.3%. That gap between first place and the rest of the field means a single company's claim portfolio is worth reviewing closely before filing in the same space, rather than assuming the field is evenly contested.

Grain boundary diffusion is a post-sintering process that introduces heavy rare earth elements, typically dysprosium or terbium, along the grain boundaries of a finished magnet rather than alloying them through the whole bulk. It raises coercivity while using far less heavy rare earth material, which is the main cost and supply-chain driver behind the technique. It shows up heavily in this dataset because the search scope was built specifically around it as one of the core technical routes alongside dysprosium reduction and hydrogen decrepitation.

Filings peaked at 143 in 2022 and eased to 83 by 2024, a -22% change over that three-year span, and several of the largest historical assignees show zero filings in the most recent tracked year. However, publication lags filing by roughly 18 months, so 2025 and 2026 figures are still incomplete and should not be read as confirmation of a continuing decline. The honest read is that 2022-2024 shows real cooling from the peak, with the very latest years too thin to call yet.

Relative to the dense core cluster of H01F magnet claims layered with B22F powder metallurgy and C22C alloy claims, sub-areas like dysprosium-free grain boundary diffusion sources, hydrogen decrepitation process optimisation, and orientation field control during pressing show comparatively thinner filing density. That doesn't guarantee those areas are open — non-patent literature and pending applications should be checked separately — but they are less crowded than the core composition-and-coating claims held by the largest assignees.

Fairly concentrated at the top: the five largest assignees hold 35.9% of the 1,291 records in scope, and the leader alone holds 165. But the drop from the top ranks to the tenth-place figure of 23 shows a long tail of smaller filers below that concentration, and co-assignee filing is rare — only 7 pairs are identified in the dataset, with most companies filing independently. That combination of a strong leader group and a fragmented tail means competitive monitoring needs to cover both the concentrated top and the wider field of individual filers.