Hysteresis branch crossing in permalloy

Abstract

For several decades, it has been widely assumed that the ascending branch of a magnetic hysteresis loop could not cross over the descending branch (and similarly, the descending branch could not cross over the ascending branch). This conclusion was based on the erroneous assumption that the hysteresis branch crossing violated the Laws of Thermodynamics (specifically, conservation of energy). More recently, it has been shown that the hysteresis branch crossing violates no fundamental law and is a robust and reproducible phenomenon in nickel thin films, deposited and annealed on lithium niobate. Here we show that the hysteresis branch crossing occurs in permalloy films, grown on silicon substrates in the presence of a magnetic field. The coercivity of the permalloy films is approximately two orders of magnitude smaller than the coercivity of the nickel films, and the mechanism which creates the magnetic anisotropy in the permalloy films is completely different. These observations seem to indicate that the crossing of hysteresis branches may be a far more common phenomenon than previously thought.