Basically, as I come to a stop, I'll feel the brake grab then ease off and grab again over and over. I feel it happens once every tire rotation, which would explain why it gets more pronounced at lower speeds.
I found this as a notice posted from Mazda "SOME VEHICLES EXHIBIT BRAKE RELATED CONCERNS SUCH AS BRAKE NOISE, BRAKE JUDDER OR BRAKE DRAGGING. IF YOU ENCOUNTER A CUSTOMER COMPLAINT FOR ANY ONE OF THESE SYMPTOMS, REFER TO THE FOLLOWING INFORMATION TO UNDERSTAND WHY SYMPTOMS MAY OCCUR, AND TO BETTER ASSIST THE CUSTOMER IN RESOLVING THEIR SPECIFIC BRAKE CONCERN."
I'll probably try to get it to a Mazda dealer soon so they can check it out.
Just as a matter of interest, how hard do you brake? I have noticed that most people will see that they are going to have to stop, and then start braking gradually until they come to a halt, while there are others that will take no notice, and just brake really hard at the last moment before coming to a halt. If you are one of the latter, maybe that could be your problem, and your car's ABS system is just reacting to your driving style.
So the frequency slows as the car slows. A couple of things happen with brakes that could be affecting yours, though I'm not saying this is your issue for sure.
There are times when pad deposits form on the rotors, usually from prolonged contact with hot brakes. These will wear off. The other is a slightly warped rotor which, IMHO is misdiagnosed rotor deposits. These come across as pulsations in the pedal.
It seems to be that your rotors are warped. If there was an ABS issue it would trigger the malfunction warning light. Take the car into the shop and reproduce the issue for the mechanic - bobs your uncle!