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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.


FORC distribution and ΔM measurements.(a–d) FORC distributions and (e) ΔM results of L10-FePt (4 nm)/A1-FePt(tA1) films where tA1 is (a) 0 nm, (b) 2 nm, (c) 5 nm and (d) 9 nm. Positive peaks of ΔM are characteristic of magnetizing (e.g. exchange) interactions, while negative ones indicate demagnetizing (e.g. dipolar) interactions. In panel (e) 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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f3: FORC distribution and ΔM measurements.(a–d) FORC distributions and (e) ΔM results of L10-FePt (4 nm)/A1-FePt(tA1) films where tA1 is (a) 0 nm, (b) 2 nm, (c) 5 nm and (d) 9 nm. Positive peaks of ΔM are characteristic of magnetizing (e.g. exchange) interactions, while negative ones indicate demagnetizing (e.g. dipolar) interactions. In panel (e) 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: Details of the magnetization reversal in L10-FePt (4 nm) /A1-FePt(tA1) were identified using the first-order reversal curve (FORC) technique22232425262728, as shown in Fig. 3. The FORC diagrams all show two key features: (1) a horizontal ridge, parallel to the H axis, and (2) a vertical ridge, essentially parallel to the HR axis. These type of features are commonly seen in PMA films which reverse by a domain nucleation/growth mechanism232930. For the L10-FePt film alone, the horizontal FORC ridge is aligned to the left of the vertical ridge (as in a flipped L-shape), Fig. 3a, noted as “left bending” hereafter. As tA1 increases to 2 nm, Fig. 3b, the FORC features remain qualitatively the same, but shift to more positive values of HR and more negative values of H. With further increase in tA1 (now > lex), the horizontal feature moves to the right of the vertical one, noted as “right-bending” hereafter (Fig. 3c,d). While both left- and right-bending features have been observed in the literature23293031323334, there has been no distinction between them nor discussion of the origin of their left/right facing orientation.


Magnetic Yoking and Tunable Interactions in FePt-Based Hard/Soft Bilayers
FORC distribution and ΔM measurements.(a–d) FORC distributions and (e) ΔM results of L10-FePt (4 nm)/A1-FePt(tA1) films where tA1 is (a) 0 nm, (b) 2 nm, (c) 5 nm and (d) 9 nm. Positive peaks of ΔM are characteristic of magnetizing (e.g. exchange) interactions, while negative ones indicate demagnetizing (e.g. dipolar) interactions. In panel (e) 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

f3: FORC distribution and ΔM measurements.(a–d) FORC distributions and (e) ΔM results of L10-FePt (4 nm)/A1-FePt(tA1) films where tA1 is (a) 0 nm, (b) 2 nm, (c) 5 nm and (d) 9 nm. Positive peaks of ΔM are characteristic of magnetizing (e.g. exchange) interactions, while negative ones indicate demagnetizing (e.g. dipolar) interactions. In panel (e) 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: Details of the magnetization reversal in L10-FePt (4 nm) /A1-FePt(tA1) were identified using the first-order reversal curve (FORC) technique22232425262728, as shown in Fig. 3. The FORC diagrams all show two key features: (1) a horizontal ridge, parallel to the H axis, and (2) a vertical ridge, essentially parallel to the HR axis. These type of features are commonly seen in PMA films which reverse by a domain nucleation/growth mechanism232930. For the L10-FePt film alone, the horizontal FORC ridge is aligned to the left of the vertical ridge (as in a flipped L-shape), Fig. 3a, noted as “left bending” hereafter. As tA1 increases to 2 nm, Fig. 3b, the FORC features remain qualitatively the same, but shift to more positive values of HR and more negative values of H. With further increase in tA1 (now > lex), the horizontal feature moves to the right of the vertical one, noted as “right-bending” hereafter (Fig. 3c,d). While both left- and right-bending features have been observed in the literature23293031323334, there has been no distinction between them nor discussion of the origin of their left/right facing orientation.

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.