  Short wave-length exchange-dominated propagating spin waves will enable
magnonic devices to operate at higher frequencies and higher data transmission
rates.1 While GMR based magnetic nano-contacts are highly efficient injectors
of propagating spin waves2,3, the generated wave lengths are 2.6 times the
nano-contact diameter4, and the electrical signal strength remains much too
weak for practical applications. Here we demonstrate nano-contact based spin
wave generation in magnetic tunnel junction stacks, and observe large discrete
frequency steps consistent with the hitherto ignored possibility of second and
third order propagating spin waves with wave lengths of 120 and 74 nm, i.e.
much smaller than the 150 nm nano-contact. These higher-order propagating spin
waves will not only enable magnonic devices to operate at much higher
frequencies, but also greatly increase their transmission rates and spin wave
propagating lengths, both proportional to the much higher group velocity.
