Enhanced moments in bcc Co1−Mn on MgO(001)

Abstract

A 40% enhancement of the Co magnetic moment has been found for thin films of bcc Co 1-x Mn x grown by molecular beam epitaxy on a 2 nm bcc Fe buffer layer on MgO(001). Although the bcc phase cannot be stabilized in the bulk, we confirm that it is stable as an epitaxial film in the composition range x = 0-0.7. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism, we show that the Co moment is a maximum of 2.38 µ B at x = 0.24, while the net Mn moment remains roughly constant until x = 0.24, then drops steadily. Mn is found to align parallel with Co for all ferromagnetic concentrations, up to x = 0.7, where the total moment of the film abruptly collapses to zero, most likely due to the onset of the observed structural instability.

Tailoring perpendicular magnetic coupling by XMCD

“…20 Compositions were determined from XAS intensity ratios and elemental moments from the intensity of the L 3 XMCD features for Co and Mn. The Co and Mn L 23 -edge XAS and XMCD are displayed in Figure 2 a pure bcc Co film (L 3 peak set to 777.90 eV) or Mn 2 O 3 reference powder (L 3 shoulder peak set to 637.97 eV) immediately after the CoMn film and shifting the energy scales.…”

“…For a bcc CoMn ultrathin film grown on MgO(100) (a MgO = 0.4212 nm), the film is pseudomorphic with the MgO surface, but rotated 45 • with respect to the MgO surface net, resulting in a CoMn = 0.2978 nm. 20 Forced registry to a substrate which is not lattice-matched often leads to a tetragonal distortion of the film. Our DFT calculations indicate that the c/a ratio at this composition is 0.86 resulting in c BCT = 0.2569 nm.…”

“…The bcc CoMn alloy film has recently shown 20 to have an increasing saturation moment with composition, reaching a maximum near Co 75 Mn 25 . Separately determining the PMA constant for the Co and Mn elements in an alloy film would be a good demonstration of the validity of the experimental method.…”

“…Details of the growth, including the RHEED pattern evolution, are reported elsewhere. 20,21 The XAS and XMCD measurements are conducted at beamline 6.3.1.1 and 4.0.2 of the Advanced Light Source of Lawrence Berkeley National Laboratories. Due to the large number of scans, the data is acquired in the fast-scan mode by acquiring sequential energy scans with either opposite magnetizations or opposite photon helicities.…”

Structure and Magnetic Properties of RIn2.9Co0.1 (R = La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Lu)

“…Therefore, it is necessary to drive the magnetic transition from antiferromagnetic to ferromagnetic and raise its Curie temperature to room temperature or even higher temperature. The magnetic phase transition could be driven by doping a minor amount of 3d transition metal such as Mn, Co …”