Unconventional magnetoresistance induced by sperimagnetism in GdFeCo

We investigate the magnetoresistance of ferrimagnetic GdFeCo across the magnetization compensation temperature $T_{\mathrm{M}}$. The magnetic field dependence of longitudinal resistivity (${\rho }_{\mathrm{xx}}$) shows opposite trends below and above $T_{\mathrm{M}}$, and the variation of ${\rho }_{\mathrm{xx}}$ with $B$ becomes more significant as the temperature decreases. The observed unconventional magnetoresistance is attributed to the sperimagnetism of GdFeCo. Further investigations on the transverse resistivity (${\rho }_{\mathrm{xy}}$) of GdFeCo unveils that, contrary to the recent reports that the transition metal dominates transport of rare-earth transition-metal ferrimagnets, the Gd contribution to magnetoresistance is comparable to the FeCo contribution, showing that the transport of GdFeCo is antiferromagnetic. Our results therefore show that ferrimagnets are a convenient platform for studying antiferromagnetic spin transport and also are potential materials that can enable antiferromagnetic spin devices.

Figure 1

(a) The distribution of the magnetic moments in an amorphous GdFeCo alloy. The brown arrows represent the Gd magnetic moments. The black and gray arrows denote the Fe and the Co respectively. (b) Schematic illustration of the sperimagnetic GdFeCo. The Gd and Fe moments are distributed with cone angles of ${\theta }_{\mathrm{Gd}}$ and ${\theta }_{\mathrm{Fe}}$. (c) Schematic of the GdFeCo device with measurement geometry.

Figure 2

(a) The Hall resistance $R_{\mathrm{xy}}$ as a function of magnetic field measured from 10 to 300 K. Different colors correspond to the different temperatures as denoted in the figure. (b) The anomalous Hall resistivity ${\rho }_{\mathrm{H}}=\left({\rho }_{xy}^{\mathrm{up}}+{\rho }_{xy}^{\mathrm{down}}\right)/2$ extracted from (a). The black symbols represent the ${\rho }_{\mathrm{H}}$ for $T$ > $T_{\mathrm{M}}$ and the orange symbols represent the ${\rho }_{\mathrm{H}}$ for $T$ < $T_{\mathrm{M}}$. The open symbols denote the opposite sign of ${\rho }_{\mathrm{H}}$.

Figure 3

(a) The resistivity ${\rho }_{\mathrm{xx}}$ measured at various temperatures without external field. The black symbols represent the ${\rho }_{\mathrm{xx}}$ for $T$ > $T_{\mathrm{M}}$ and the orange symbols represent the ${\rho }_{\mathrm{xx}}$ for $T$ < $T_{\mathrm{M}}$. (b) The variation of ${\rho }_{\mathrm{xx}}$ as a function of magnetic field for various temperature. Different colors correspond to the different temperatures as denoted in the figure. (c) The extracted result for $T=100\mathrm{K}$ with schematic illustrations of two submoments.

Figure 4

(a) The extracted field-dependent resistivity variation for $B_Z=+2\mathrm{T}$ to 0 T from Fig. 3. (b) The slope of ${\rho }_{\mathrm{xx}}-B$ extracted from (a). The black symbols represent the slope $\mathrm{\Delta }{\rho }_{\mathrm{xx}}/B$ for $T$ > $T_{\mathrm{M}}$ and the orange symbols represent the $\mathrm{\Delta }{\rho }_{\mathrm{xx}}/B$ for $T$ < $T_{\mathrm{M}}$. Open symbols denote the opposite sign of $\mathrm{\Delta }{\rho }_{\mathrm{xx}}/B$. (c) The slope of ${\rho }_{\mathrm{xy}}-B$ extracted from Fig. 2. The black symbols represent the slope $\mathrm{\Delta }{\rho }_{\mathrm{xy}}/B$ for $T$ > $T_{\mathrm{M}}$ and the orange symbols represent the $\mathrm{\Delta }{\rho }_{\mathrm{xy}}/B$ for $T$ < $T_{\mathrm{M}}$.