National High Magnetic Field Laboratory has one. Covers only about 5 meters,
(1) but if it sucks in a ferropurrous cat, you’ll never see the beast again. Beyond that distance the cat will only get slightly tilted. Not sure, how much they charge for moving it to your house.
Others will correct your beliefs below, but even without that: let’s look at what you propose. You believe that “electromagnetic field has a negative effect on living things.” So your idea is to shoot yourself and everybody around with one. You need no knowledge of physics, electronics, or maths to see something is off with the idea, do you? Rationalizing it through distance isn’t going to work. If your original premise was right, the harmful effect wouldn’t instantly drop to zero after the 10 meters mark.
Fortunately it doesn’t. Neither electromagnetic field nor waves in that field have any known harmful effect on living organisms. Associating word “electromagnetic,” or just any arbitrary kind of radiation, with harm is a common misconception, and also disinformation associated with it. Not only you’re swimming in all kinds of electromagnetic radiation all the time, not only it’s crucial for survival of any known life, but at this very moment you’re emitting around 100 watts of electromagnetic radiation. At frequencies closer to carcinogenic and ionizing radiation than anything you’d ever obtain in any electric circuit.
If you want to get rid of cats, consider chemical repelents like
IBI-246 and similar. Combined with understanding what causes the problem: trying to limit it, or redirect cats’ attention to other places.
Ultrasonic devices supposedly work, but there are two problems. First: it’s not some magical feature of ultrasonic waves, but simple noise that makes cats unwilling to be in the affected area. While higher frequencies may be less comfortable to cats, the pitch is so chosen primarily to not disturb humans. Since it’s nothing but noise, animals may either not hear it at all (hearing problems are not only a human thing), not be sensitive to it, or… adjust to it, if the incentive is high enough. The second problem is that many such devices are fakes.
It also takes time for any measure to take effect. A cat will not sit in cold simply because there is something unpleasant in a warm place. It needs to have somewhere else to go. Not to mention cats are clever beasts. They learn pretty quickly to find safe spots and avoid nuisance.
(1) From Veritasium: