  Nanoscale single-domain bar magnets are building blocks for a variety of
fundamental and applied mesoscopic magnetic systems, such as artificial spin
ices, magnetic shape-morphing microbots as well as magnetic majority logic
gates. The magnetization reversal switching field of the bar nanomagnets is a
crucial parameter that determines the physical properties and functionalities
of their constituted artificial systems. Previous methods on tuning the
magnetization reversal switching field of a bar nanomagnet usually rely on
modifying its aspect ratio, such as its length, width and/or thickness. Here,
we show that the switching field of a bar nanomagnet saturates when extending
its length beyond a certain value, preventing further tailoring of the
magnetization reversal via aspect ratios. We showcase highly tunable switching
field of a bar nanomagent by tailoring its end geometry without altering its
size. This provides an easy method to control the magnetization reversal of a
single-domain bar nanomagnet. It would enable new research and/or applications,
such as designing artificial spin ices with additional tuning parameters,
engineering magnetic microbots with more flexibility as well as developing
magnetic quantum-dot cellular automata systems for low power computing.
