Distinguishing antiferromagnetic spin sublattices via the spin Seebeck effect

We measured spin Seebeck signals at the top and bottom surfaces of an antiferromagnetic ${\mathrm{Cr}}_2{\mathrm{O}}_3$ film, using a $\mathrm{Pt}/{\mathrm{Cr}}_2{\mathrm{O}}_3/\mathrm{Pt}$ trilayer. Our experimental data, combined with micromagnetic simulations, clearly demonstrate that the uncompensated sublattice at the top and bottom surfaces plays a decisive role in determining the symmetry of the spin Seebeck signals, providing fundamental insight for understanding the generation of spin Seebeck signal in antiferromagnetic materials.

Figure 1

(a) Illustration of the spin structure of a ${\mathrm{Cr}}_2{\mathrm{O}}_3$ single crystal with a stepped (0001) surface. The red and green arrows denoted the different spin directions of ${\mathrm{Cr}}^{3+}$ ions. (b) $\theta \text{−}2\theta$ x-ray diffraction pattern of a 180-nm ${\mathrm{Cr}}_2{\mathrm{O}}_3$ film (lower panel) and ${\mathrm{Cr}}_2{\mathrm{O}}_3$ (180 nm)/Pt(5 nm) bilayer (upper panel), respectively. The films are deposited on ${\mathrm{Al}}_2{\mathrm{O}}_3$ (0001) substrates. (c) Experimental setup of the SSE measurements. The left figure is the top view of the device. The insert on the right shows the cross section of the sample structure.

Figure 2

Angular dependence of the SSE voltages at the top and bottom surfaces of ${\mathrm{Cr}}_2{\mathrm{O}}_3$ at different fields. In (a) and (b), The upper figures represent the signals measured at the top Pt layer, while the lower figures represent the signals measured at the bottom Pt layer. The magenta and light blue colors represent the signals when the field rotates 0 ° → 360 ° and back 360 ° → 0 °, respectively. The temperature during these measurements was 100 K.

Figure 3

Simulation of the angular magnetic field dependence of the sublattice moments at 6 and 8 T, respectively. In (a) and (f), from top down, are plots of the normalized $m_y$ at the bottom surface ($m_y^{i=1}$), top surface ($m_y^{i=30}$), and the net moment (${\sum }_{i=1}^{30}{m}_y^i$). The solid and dash lines represent the field rotating 0 ° → 360 ° and rotate back 360 ° → 0 °, respectively. The blue dashed lines are guidelines for the selected field angles ${\theta }_H$, at which the magnetization configurations are plotted, as (b)–(e) and (g)–(j) show. The small arrows in (b)–(e) and (g)–(j) indicate the sublattices in each layer. The colors denote $m_y$, as shown in the color bar. The number on the left side of (b) and (f) denote the layer number $i$.

Figure 4

Distinguishing opposite sublattice configuration in uniaxial ${\mathrm{Cr}}_2{\mathrm{O}}_3$. Panels (a) and (b) show the angular dependence of the SSE signals at the top and bottom surfaces with opposite initial sublattice directions, indicated by the insets. The temperature during the measurements was 100 K. The field amplitude is 6 T.