Effect of Al interlayers on growth and magneto-optic properties of MnBi thin films

Rüdiger, Ulrich; Fumagalli, P.; Berndt, H.; Schirmeisen, André; Güntherodt, G.; Holländer, B.

doi:10.1063/1.362781

Cited by 9 publications

(13 citation statements)

References 14 publications

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“…Details of the experimental setup are given in Ref. 6. Before annealing, a clear separation of the individual Bi and Mn layers was observed as a double-peak structure.…”

Section: ͓S0003-6951͑97͒01619-7͔mentioning

confidence: 99%

“…Nevertheless, the coercive field of 0.5 T and, as a consequence, the microcrystalline structure of MnBi particles do not change. 6,7 The rectangular-shaped hysteresis loops exhibit a squareness of nearly one.…”

Section: ͓S0003-6951͑97͒01619-7͔mentioning

confidence: 99%

“…The deposition rates of the Bi and Mn layers were fixed to 0.4 and 2.0 Å/s, respectively. 6 The Bi/Mn bilayers are separated from each other by 2.0-nm-thick Al interlayers and covered by a 2.0-nm-thick Al capping layer. In order to get c-axis oriented MnBi films the multilayers were annealed for 30 min at 653 K and for 30 min at 593 K. During annealing the vacuum stayed in the range from 10 Ϫ5 mbar.…”

Section: ͓S0003-6951͑97͒01619-7͔mentioning

confidence: 99%

“…6 The diffusion profile across the Bi/Mn/Al stacks was studied by RBS measurements using 1.4 MeV He ϩ ions. Details of the experimental setup are given in Ref.…”

Section: ͓S0003-6951͑97͒01619-7͔mentioning

confidence: 99%

“…The samples were mounted on a heatable copper rod which allows for a temperature adjustment up to 730 K with an uncertainty of Ϯ5 K. Details of the preparation procedure and the structural properties of MnBi and MnBiAl films were published elsewhere. 6 The temperature dependence of the coercive field, H c , and the saturation magnetization, M s , as obtained from polar Kerr hysteresis loops, are plotted in Fig. 1.…”

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Suppression of the increase of high-temperature coercivity in MnBi thin films by Al interlayers

Rüdiger

Roos

Güntherodt

et al. 1997

Applied Physics Letters

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By tailoring the microcrystalline structure of MnBi films, using Al interlayers, a reduction of the high-temperature coercivity by a factor of 3 is achieved. The separation of Bi/Mn bilayers by Al interlayers acts as a diffusion barrier perpendicular to the surface. After annealing, the MnBi layers contain single-domain particles surrounded by an Al matrix exhibiting no significant increase of the coercive field with increasing temperature. ͓S0003-6951͑97͒01619-7͔The large negative Kerr rotation of nearly ⌰ K ϭϪ1.2°i n the UV spectral region and the large perpendicular magnetic anisotropy make MnBi a promising material for highdensity, short-wavelength magneto-optic recording. 1 A laser beam is commonly used for reading and writing. As a consequence, the smallest diffraction-limited spot-size diameter is 0.56 /NA. The spot size can be reduced not only by decreasing the wavelength but also by increasing the numerical aperture NA. The recently developed blue semiconductor lasers with ϭ417 nm reduce the theoretical spot-size minimum to nearly 240 nm. Therefore, in order to get a low-noise readout signal, the diameter of the crystallites has to be minimized to sizes smaller than 25 nm. A MnBi grain size of more than Ϸ1 m in diameter gives rise to a small signal-to-noise ratio of the readout signal. 1 The grain size reduces by adding a small content of Al, Sb or Pt to the MnBi films. 2,3 For example, MnBi films with Al interlayers exhibit grain sizes smaller than about 100 nm in diameter. 2 An unusual increase of the coercive field, H c , reaching 2.0 T at 550 K is detrimental to the thermomagnetic writing process. 4 Several years ago, a hybrid domain-wall-pinning model was proposed to explain the temperature dependence of the coercive field. 5 The main feature of this model is the thermal activation of domain walls pinned by nonmagnetic defects or impurities during the magnetization-reversal process. In the case of single-domain particles, a temperaturedependent pinning mechanism of domain walls is not important. By comparing the magnetic energy of a single-domain MnBi sphere with that of a sphere showing internal flux closure, the upper limit in size for a single-domain state is estimated to be nearly 100 nm. For calculating this critical diameter a Bloch-wall energy of S B ϭ0.016 J/m 2 , a saturation magnetization of M S ϭ660 kA/m, and a uniaxial anisotropy constant K u ϭ1160 kJ/m 3 were used. 5 In this letter, we show that adding Al interlayers to MnBi in a suitable way will reduce MnBi grain size below 100 nm and, therefore, effectively suppress the domain-wall pinning mechanism. This leads to a vanishing of the strong increase of H c between room temperature and 550 K.A sequence of three Bi ͑18 nm͒/Mn ͑12 nm͒ bilayers has been deposited on quartz substrates in a vacuum of ϳ10 Ϫ6 mbar. The deposition rates of the Bi and Mn layers were fixed to 0.4 and 2.0 Å/s, respectively. 6 The Bi/Mn bilayers are separated from each other by 2.0-nm-thick Al interlayers and covered by a 2.0-nm-thick Al capping layer. In order t...

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“…Details of the experimental setup are given in Ref. 6. Before annealing, a clear separation of the individual Bi and Mn layers was observed as a double-peak structure.…”

Section: ͓S0003-6951͑97͒01619-7͔mentioning

confidence: 99%

Section: ͓S0003-6951͑97͒01619-7͔mentioning

confidence: 99%

Section: ͓S0003-6951͑97͒01619-7͔mentioning

confidence: 99%

“…6 The diffusion profile across the Bi/Mn/Al stacks was studied by RBS measurements using 1.4 MeV He ϩ ions. Details of the experimental setup are given in Ref.…”

Section: ͓S0003-6951͑97͒01619-7͔mentioning

confidence: 99%

mentioning

confidence: 99%

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