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Magnetic Yoking and Tunable Interactions in FePt-Based Hard/Soft Bilayers

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ABSTRACT

Magnetic interactions in magnetic nanostructures are critical to nanomagnetic and spintronic explorations. Here we demonstrate an extremely sensitive magnetic yoking effect and tunable interactions in FePt based hard/soft bilayers mediated by the soft layer. Below the exchange length, a thin soft layer strongly exchange couples to the perpendicular moments of the hard layer; above the exchange length, just a few nanometers thicker, the soft layer moments turn in-plane and act to yoke the dipolar fields from the adjacent hard layer perpendicular domains. The evolution from exchange to dipolar-dominated interactions is experimentally captured by first-order reversal curves, the ΔM method, and polarized neutron reflectometry, and confirmed by micromagnetic simulations. These findings demonstrate an effective yoking approach to design and control magnetic interactions in wide varieties of magnetic nanostructures and devices.

No MeSH data available.


Magnetometry.Major hysteresis loops of L10-FePt (4 nm)/A1-FePt (tA1) bilayer films in the (a) perpendicular and (b) in-plane orientation, normalized to the saturation magnetic moment of the L10-FePt. Samples are identified by color and symbol for tA1 = 0 nm (black squares), 2 nm (red circles), 5 nm (blue triangles) and 9 nm (green inverted triangles).
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f1: Magnetometry.Major hysteresis loops of L10-FePt (4 nm)/A1-FePt (tA1) bilayer films in the (a) perpendicular and (b) in-plane orientation, normalized to the saturation magnetic moment of the L10-FePt. Samples are identified by color and symbol for tA1 = 0 nm (black squares), 2 nm (red circles), 5 nm (blue triangles) and 9 nm (green inverted triangles).

Mentions: Thin film bilayers of L10-Fe52Pt48 (4 nm)/A1-Fe52Pt48 (tA1) with tA1 = 0 nm–9 nm were fabricated by sputtering, as described in Methods. Magnetometry measurements were performed at room temperature in the out-of-plane geometry, unless otherwise noted. Hysteresis loops for the films are shown in Fig. 1. For the 4 nm L10-FePt film alone (tA1 = 0 nm), a square hysteresis loop is observed with a coercivity of 320 mT in the perpendicular geometry (panel a), while the in-plane loop is closed (panel b), indicating a clear perpendicular anisotropy expected of (001) oriented L10-FePt. For films with increasing tA1, in the perpendicular geometry the coercivity decreases and the loop develops a strong canting; magnetic moments associated with the slope are due to the in-plane soft layer, which is being reversibly forced out-of-plane by the field. Note that for the sample with tA1 = 2 nm, the hysteresis loops are very similar to those for the L10-FePt alone, suggesting that the A1 layer orientation is dominated by the L10 layer through exchange coupling; this is consistent with the A1-layer’s exchange length of lex = 3.9 nm21. Once tA1 exceeds lex, significant in-plane magnetization is observed for tA1 = 5 nm and even more so for tA1 = 9 nm (Fig. 1), indicating more and more of the moments in the A1 layer are now in the film plane. The development of this in-plane reversal indicates that the A1 layer is able to switch with only limited dependence on the perpendicular L10 layer.


Magnetic Yoking and Tunable Interactions in FePt-Based Hard/Soft Bilayers
Magnetometry.Major hysteresis loops of L10-FePt (4 nm)/A1-FePt (tA1) bilayer films in the (a) perpendicular and (b) in-plane orientation, normalized to the saturation magnetic moment of the L10-FePt. Samples are identified by color and symbol for tA1 = 0 nm (black squares), 2 nm (red circles), 5 nm (blue triangles) and 9 nm (green inverted triangles).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5015099&req=5

f1: Magnetometry.Major hysteresis loops of L10-FePt (4 nm)/A1-FePt (tA1) bilayer films in the (a) perpendicular and (b) in-plane orientation, normalized to the saturation magnetic moment of the L10-FePt. Samples are identified by color and symbol for tA1 = 0 nm (black squares), 2 nm (red circles), 5 nm (blue triangles) and 9 nm (green inverted triangles).
Mentions: Thin film bilayers of L10-Fe52Pt48 (4 nm)/A1-Fe52Pt48 (tA1) with tA1 = 0 nm–9 nm were fabricated by sputtering, as described in Methods. Magnetometry measurements were performed at room temperature in the out-of-plane geometry, unless otherwise noted. Hysteresis loops for the films are shown in Fig. 1. For the 4 nm L10-FePt film alone (tA1 = 0 nm), a square hysteresis loop is observed with a coercivity of 320 mT in the perpendicular geometry (panel a), while the in-plane loop is closed (panel b), indicating a clear perpendicular anisotropy expected of (001) oriented L10-FePt. For films with increasing tA1, in the perpendicular geometry the coercivity decreases and the loop develops a strong canting; magnetic moments associated with the slope are due to the in-plane soft layer, which is being reversibly forced out-of-plane by the field. Note that for the sample with tA1 = 2 nm, the hysteresis loops are very similar to those for the L10-FePt alone, suggesting that the A1 layer orientation is dominated by the L10 layer through exchange coupling; this is consistent with the A1-layer’s exchange length of lex = 3.9 nm21. Once tA1 exceeds lex, significant in-plane magnetization is observed for tA1 = 5 nm and even more so for tA1 = 9 nm (Fig. 1), indicating more and more of the moments in the A1 layer are now in the film plane. The development of this in-plane reversal indicates that the A1 layer is able to switch with only limited dependence on the perpendicular L10 layer.

View Article: PubMed Central - PubMed

ABSTRACT

Magnetic interactions in magnetic nanostructures are critical to nanomagnetic and spintronic explorations. Here we demonstrate an extremely sensitive magnetic yoking effect and tunable interactions in FePt based hard/soft bilayers mediated by the soft layer. Below the exchange length, a thin soft layer strongly exchange couples to the perpendicular moments of the hard layer; above the exchange length, just a few nanometers thicker, the soft layer moments turn in-plane and act to yoke the dipolar fields from the adjacent hard layer perpendicular domains. The evolution from exchange to dipolar-dominated interactions is experimentally captured by first-order reversal curves, the ΔM method, and polarized neutron reflectometry, and confirmed by micromagnetic simulations. These findings demonstrate an effective yoking approach to design and control magnetic interactions in wide varieties of magnetic nanostructures and devices.

No MeSH data available.