Coexistence of soft and hard magnetic phases in single layer amorphous Tb–Co thin films

Journal Article · Wed Jan 19 00:00:00 EST 2022 · Journal of Applied Physics

DOI:https://doi.org/10.1063/5.0074314· OSTI ID:1960391

Ceballos, A.  ^[1]; Charilaou, M.  ^[2]; Molina-Ruiz, M.  ^[1]; Hellman, F.  ^[3]

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1. University of California, Berkeley, CA (United States)
2. University of Louisiana, Lafayette, LA (United States)
3. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); University of California, Berkeley, CA (United States)

Amorphous, ferrimagnetic Tb–Co thin films prepared with a thin Ta underlayer and either a Ta or a Pt overlayer show evidence of both soft and hard magnetic phases. At room temperature, the films exhibit conventional ferromagnetism, but low temperature magnetometry measurements reveal the decoupling of the two magnetic phases with decreasing temperature due to increased anisotropy energy of the hard layer at lower temperatures. Decreasing the film thickness to 2 nm, slightly above the superparamagnetic limit found at 1 nm, a soft, low-density phase was isolated and found to be present in all the films as confirmed with x-ray reflectivity and Rutherford backscattering spectrometry measurements. For greater thicknesses, the bottom layer retains its soft magnetic nature, while the remainder of the film is denser and has strong perpendicular magnetic anisotropy, leading to the exchange-spring behavior when the anisotropy becomes large, either at low temperatures or via a Pt overlayer that adds a strong interfacial anisotropy to the layer. Micromagnetic simulations of a soft/hard bilayer model with the experimentally determined anisotropy and magnetization parameters into a soft/hard bilayer model reproduced the experimental hysteretic behavior very well. These findings demonstrate how the magnetic state and the response of a-Tb–Co films to external fields can be controlled, providing a high degree of tunability that is promising for high-performance nanoscale devices.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division; National Science Foundation (NSF); Louisiana Board of Regents; USDOE
• Grant/Contract Number: AC02-05CH11231; DGE 1106400; LEQSF(2020-23)-RD-A-32; AC02-05-CH11231
• OSTI ID: 1960391
• Alternate ID(s): OSTI ID: 1841055
• Journal Information: Journal of Applied Physics, Vol. 131, Issue 3; ISSN 0021-8979
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

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36 MATERIALS SCIENCE