-Temperature Dependence of Magnetic Anisotropy of MnBi and MnAl Thin Films-
Claudia Mewes1,4 and Takahiro Suwa1,5
1Center for Materials for Information Technology (MINT)
2Department of Metallurgical and Materials Engineering
3Department of Electrical and Computer Engineering
4Department of Physics The University of Alabama, Tuscaloosa, AL 35487-0209, U.S.A.
5Materials Development Center, TDK Corporation, Narita, Japan
Abstract:
Among various high magnetic anisotropy materials without rare-earth elements, the low temperature phase (LTP) MnBi compound exhibits a unique behavior of the temperature dependence of magnetic anisotropy constant K, which increases with temperature above around 100K. However, very little systematic studies on the temperature dependence of K for the LTP MnBi compound have been found in literature1,2.
The present study has been motivated to systematically investigate into magnetic anisotropy of LTP MnBi and τ-phase MnAl thin films.
Multilayers of Mn/Bi and Mn/Al were fabricated by sputter-deposition onto silica-glass substrates at an ambient temperature during deposition. The samples thus deposited were followed by a post annealing at a temperature Ta from around 300 ⁰C to 550 ⁰C in vacuum3.
The MnBi samples annealed at Ta = 550⁰C for 0.5hr. are found to possess the <001> orientation along the film normal, while those annealed at Ta = 350 ⁰C for 15 hr. are found to be of the LTP phase with no preferential crystallographic orientation. Measurements of perpendicular magnetic anisotropy constant K were carried out by a torque method in fields up to 9T over a temperature range from 100K to 400K. The K is found to increase with T, in similar to the results of bulk1. The correlation between magnetic anisotropy constant K and saturation magnetization Ms for the <001> oriented sample is found to be K ≈ M-8. For the case of tau-MnAl thin films, it is found that K is proportionally to M over the temperature range from 4 to 400K.
Measurements of lattice constants a and c for the LTP MnBi thin films were also carried out over a temperature range from 300 to 550K. A recent theoretical work4 on the magnetic anisotropy energy as a function of lattice constant suggested the the latice constant a is significantly influence on the magnetic anisotroy energy. The present result is found to be qualitatively consitent with this theory, but not in quatitatively.
The effect of the growth orientation of LTP MnBi thin films deposited onto single crystals with various orientations on magnetic anisotropy is also discussed.
The present work was in part supported by NSF-CMMI #1229049 (G8 Project) and by TDK.
References:
1. T.Chen and W.E.Stutius: IEEE Trans.Mag-10, 581-586 (1974).
2. J.B.Yang, W.B.Yellon, W.J.James et al.: J. Phys. Cond. Matter. 14, 6509-6519 (2002).
3. T. Hozumi, P.LeClair, G.Mankey et al., J. Appl. Phys., 115, 17A737 1-3 (2014).
4. N.A.Zarkevich, L.-L.Wang and D.D.Johnson: APL Materials 2, 032103 1-6 (2014).
The present study has been motivated to systematically investigate into magnetic anisotropy of LTP MnBi and τ-phase MnAl thin films.
Multilayers of Mn/Bi and Mn/Al were fabricated by sputter-deposition onto silica-glass substrates at an ambient temperature during deposition. The samples thus deposited were followed by a post annealing at a temperature Ta from around 300 ⁰C to 550 ⁰C in vacuum3.
The MnBi samples annealed at Ta = 550⁰C for 0.5hr. are found to possess the <001> orientation along the film normal, while those annealed at Ta = 350 ⁰C for 15 hr. are found to be of the LTP phase with no preferential crystallographic orientation. Measurements of perpendicular magnetic anisotropy constant K were carried out by a torque method in fields up to 9T over a temperature range from 100K to 400K. The K is found to increase with T, in similar to the results of bulk1. The correlation between magnetic anisotropy constant K and saturation magnetization Ms for the <001> oriented sample is found to be K ≈ M-8. For the case of tau-MnAl thin films, it is found that K is proportionally to M over the temperature range from 4 to 400K.
Measurements of lattice constants a and c for the LTP MnBi thin films were also carried out over a temperature range from 300 to 550K. A recent theoretical work4 on the magnetic anisotropy energy as a function of lattice constant suggested the the latice constant a is significantly influence on the magnetic anisotroy energy. The present result is found to be qualitatively consitent with this theory, but not in quatitatively.
The effect of the growth orientation of LTP MnBi thin films deposited onto single crystals with various orientations on magnetic anisotropy is also discussed.
The present work was in part supported by NSF-CMMI #1229049 (G8 Project) and by TDK.
References:
1. T.Chen and W.E.Stutius: IEEE Trans.Mag-10, 581-586 (1974).
2. J.B.Yang, W.B.Yellon, W.J.James et al.: J. Phys. Cond. Matter. 14, 6509-6519 (2002).
3. T. Hozumi, P.LeClair, G.Mankey et al., J. Appl. Phys., 115, 17A737 1-3 (2014).
4. N.A.Zarkevich, L.-L.Wang and D.D.Johnson: APL Materials 2, 032103 1-6 (2014).