Deposition and patterning of magnetic atom trap lattices in FePt films with periods down to 200 nm

Abstract

We report on the epitaxial growth and the characterization of thin FePt films and the subsequent patterning of magnetic lattice structures. These structures can be used to trap ultracold atoms for quantum simulation experiments. We use molecular beam epitaxy to deposit monocrystalline FePt films with a thickness of 50 nm. The films are characterized with X-ray scattering and M€ ossbauer spectroscopy to determine the long range order parameter and the hard magnetic axes. A high monocrystalline fraction was measured as well as a strong remanent magnetization of M ¼ 900 kA/m and coercivity of 0.4 T. Using electron beam lithography and argon ion milling, we create lattice patterns with a period down to 200 nm, and a resolution of 30 nm. The resulting lattices are imaged in a scanning electron microscope in the cross-section created by a focused ion beam. A lattice with continuously varying lattice constant ranging from 5 lm down to 250 nm has been created to show the wide range of length scales that can now be created with this technique.

Designs of magnetic atom-trap lattices for quantum simulation experiments

“…We describe structures made out of perpendicularly magnetized films, patterned in a binary fashion; i.e., we assume that in any given location on the chip we have either the full film thickness or no magnetic material at all. Instead of the bulk magnetization M we use the twodimensional magnetization, i.e., the magnetic dipole per unit area: I M = M h. Our recently constructed experiment houses a chip with a 50 nm thick film of magnetized FePt with a magnetization of M = 800 kA/m [15]. Because several structures that we will present have been realized on this chip, we will consider this thickness and equivalent edge current I M = 0.04 A.…”

“…The kagome and honeycomb structure have been created in a 50 nm thick film of magnetized FePt. The fabrication of these magnetic structures is discussed in full detail in a separate paper [15]. In Fig.…”

“…No such edge effects are present in any of the presented lattices. In the experiments we typically prevent these effects in a similar way by surrounding our lattices with a region several millimeters wide containing other lattices such that we maintain a 50% magnetic coverage [15].…”

“…Finally, in Sec. V a tapered lattice is presented wherein a varying lattice spacing yields tapered structures which provide a natural bridge between traps at the Rydberg scale and nanoscale magnetic lattices which have recently been introduced [15][16][17]. The extra applications that these barriers and tapered structures have on subwavelength magnetic traps will be discussed in a separate paper.…”

Time Evolution of Long‐Range Ordering in Fe–Pt Alloys

“…At high temperatures, Fe-Pt alloys are disordered with fcc crystal structure in the whole concentration range.An overview of the literature shows that the main techniques to define a long-range order (LRO) parameter in Fe-Pt alloys experimentally are electron diffraction, [8] X-ray scattering, and Mössbauer spectroscopy. [9] The current theoretical approaches are based on the first-principles calculations, [10] and use computational methods such as MD [11] and Monte Carlo. [12] Current research is dedicated to the calculation of the kinetics of the LRO parameter for iron-and platinum-based fcc Fe-Pt alloys.…”