Chiral Coupling between Magnetic Layers with Orthogonal Magnetization

We report on the occurrence of strong interlayer Dzyaloshinskii-Moriya interaction (DMI) between an in-plane magnetized Co layer and a perpendicularly magnetized TbFe layer through a Pt spacer. The DMI causes a chiral coupling that favors one-handed orthogonal magnetic configurations of Co and TbFe, which we reveal through Hall effect and magnetoresistance measurements. The DMI coupling mediated by Pt causes effective magnetic fields on either layer of up to 10–15 mT, which decrease monotonically with increasing Pt thickness. Ru, Ta, and Ti spacers mediate a significantly smaller coupling compared to Pt, highlighting the essential role of Pt in inducing the interlayer DMI. These results are relevant to understand and maximize the interlayer coupling induced by the DMI as well as to design spintronic devices with chiral spin textures.

Figure 1

Schematic representation of the interfacial DMI coupling illustrating the intralayer (left) and interlayer (right) coupling scenarios. The black and gray arrows represent local magnetization in the FM layers with OOP and IP magnetic anisotropy, respectively.

Figure 2

(a) Sketch of the multilayer structure (only relevant layers are labeled) and coordinate system. The block arrows indicate the magnetization of the top and bottom layers. (b) Device micrograph, electrical connections, and coordinate system. $j$ is the current density, ${\phi }_B$ is the in-plane field angle. (c) Hall resistance of $\mathrm{TbFe}(8)/\mathrm{Co}(0.4)/\mathrm{Pt}(1.2)/\mathrm{Co}(3)$ during a sweep of the OOP field ($B_z$). (d) Separation of $R_H$ due to the top Co layer ($M_{\text{Co}}$) and bottom $\mathrm{TbFe}/\mathrm{Co}$ layer ($M_{\text{TbFe}}$) obtained from the data shown in (c) by assuming a linear field dependence for $M_{\text{Co}}$ between $\pm 0.3\mathrm{T}$ and constant $R_H$ for $M_{\text{TbFe}}$ outside the coercivity region.

Figure 3

(a) Schematics of the field sweep measurements with tilt angle favoring and opposing the interlayer DMI (top left and right, respectively). The bottom diagram shows the geometry employed for the magnetoresistance measurements. (b) Hall resistance of $\mathrm{TbFe}(8)/\mathrm{Co}(0.4)/\mathrm{Pt}(1.5)/\mathrm{Co}(3)$ measured during a field sweep at ${\theta }_B=15°$ tilted along $\mathit{D}\times \mathit{z}$ (red line, initial ${\phi }_B=315°$) and along $-\mathit{D}\times \mathit{z}$ (black line, initial ${\phi }_B=135°$). (c) Coercivity difference $\mathrm{\Delta }{\mathrm{B}}_c$ as a function of ${\phi }_B$. The line is a fit to the data (see text). (d) Magnetoresistance as a function of the IP field for two different orientations of $M_{\text{TbFe}}$. The IP field is applied at ${\phi }_B=0°$ such that the positive field direction has a positive projection on $+\mathit{D}\times \mathit{z}$. $\mathrm{\Delta }{B}_s$ is the difference between the IP switching fields of $M_{\text{Co}}$ that is used to quantify $B_{\mathrm{DMI}}$ acting on the Co layer.

Figure 4

Effective $B_{\mathrm{DMI}}$ acting on (a) TbFe and (b) Co as a function of the Pt thickness. The error bars in (a) represent the standard deviation of the sinusoidal fit to the angular-dependent $\mathrm{\Delta }{B}_c$. The relative errors in (b) are estimated to be about 5% due to uncertainties in determining the position of the magnetoresistance minima.

Figure 5

(a)–(d) Coercivity difference $\mathrm{\Delta }{B}_c$ as a function of ${\phi }_B$ for samples with Pt, Ti, Ru, and Ta spacers. The spacer thickness was fixed to 1.7 nm while keeping all other layers nominally the same.