I had some magnets lying around and as I was playing with them I remembered about the Halbach array, a special arrangement of permanent magnets such that you get a very strong field on one side and weak field on the other. The only issue is that permanent magnets do not want to stay arranged this way: they'll quickly rotate and snap together in an aligned direction.
So I quickly mocked up a little Halbach array holder, which I (3d) printed. Here it is next to a Swiss 2 CHF coin:
And here again with 5 1/2-cm magnets loaded inside.
Here's a video of me loading the magnets. Starting with a stack of aligned magnets, I push them in one-by-one, rotating between each accordingly.
Here's a video testing the different magnetic strengths of each side against my metal desk frame.
You can download the STL model of the Halbach array holder. I "modeled" it in matlab generating first a hollow box and then adding a small 3-sided lip at one end to make it easier to load in the magnets.
I also generated these blueprint-style images in matlab.