Abstract
Measurements of magnetization [M(H, T)] and anomalous Hall resistance [Rxy(H, T)] are performed over a broad range of magnetic field (H) and temperatures (T) on sputter deposited 10 nm thick films of (FeCo)1−xGdx. The Gd content (x) in the films was changed by varying the Gd source power from 20 W to 50 W, in steps of 5 W. The saturation magnetization (Ms) of these films at 300 K shows a distinct minimum for the source power of 40 W. Measurements of M(H) for the 40 W sample at several temperatures establish full compensation of the antiferromagnetically coupled magnetic sublattices of Gd and FeCo at Tcomp = 270 K ± 10 K. The approach to compensation is characterized by the emergence of perpendicular magnetic anisotropy (PMA) and a diverging coercive field. The Rxy (H) of this sample, as well as of those prepared at 30 W and 50 W, scales with M(H) at T > Tcomp and T < Tcomp. However, this scaling fails in the vicinity of Tcomp where the Rxy undergoes a sign reversal. Our analysis of these data in the framework of the existing models for Rxy(H, T) in ferrimagnets suggests that the role of spin disorder and its topological contribution to Rxy may be necessary to account for the observed behavior. A precise identification of Tcomp is also important to stabilize technologically useful non-trivial spin textures and PMA in these systems.
Highlights
INTRODUCTIONThe magnetic state of amorphous thin films of transition metal (TM)–rare earth (RE) alloys has been a topic of intense research for the past several decades.[1,2,3,4,5,6,7,8,9,10,11,12] The ordering of the 3d and 4f spins of the TM and RE elements, respectively, is fundamentally important due to 3d–4f antiferromagnetic exchange that results in two magnetic sublattices, which compete, leading to compensation effects,[3,4,10,11] field and temperature driven spin-flop transitions,[8,9,12] and strong orbital magnetism.[4]
One sees a significant lowering of the saturation magnetization (Ms) together with the emergence of perpendicular magnetic anisotropy (PMA) and diverging coercive fields (Hc).[11,12,13,14,15,16]
While it has been suggested that the anomalous Hall effect (AHE) in transition metal (TM)–RE alloys is dominated by 3d sublattice magnetization,[19,29] extraneous effects such as interface pinning may influence the sign of the Hall signal.[35]
Summary
The magnetic state of amorphous thin films of transition metal (TM)–rare earth (RE) alloys has been a topic of intense research for the past several decades.[1,2,3,4,5,6,7,8,9,10,11,12] The ordering of the 3d and 4f spins of the TM and RE elements, respectively, is fundamentally important due to 3d–4f antiferromagnetic exchange that results in two magnetic sublattices, which compete, leading to compensation effects,[3,4,10,11] field and temperature driven spin-flop transitions,[8,9,12] and strong orbital magnetism.[4]. The strength of exchange interactions varies depending on the choice of the 3d ferromagnetic metals and 4f elements, and RE–TM alloys offer a wide playing field to study non-trivial magnetism The physics of these alloys has been in focus due to their technological potential as bubble memories,[24,25] thermomagnetic recording platforms,[26] all optical switching media,[27,28] and spin torque devices.[15,16,29,30] Amorphous thin films of (Fe1−xCox)yGd1−y are one archetypical 3d–4f system. We focus on the measurements of the AHE in FeCoGd amorphous films as a function of the relative concentration of TM and RE elements over a broad range of temperatures and magnetic field in order to establish correlations between M(H) and Rxy(H), on the behavior of Rxy near Tcomp, and on the sign of the anomalous Hall voltage
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
