Electrical detection of the spin reorientation transition in antiferromagnetic $\mathrm{Tm}\mathrm{Fe}{\mathrm{O}}_3$ thin films by spin Hall magnetoresistance

$\mathrm{Tm}\mathrm{Fe}{\mathrm{O}}_3$ (TFO) is a canted antiferromagnet that undergoes a spin reorientation transition (SRT) with temperature between 82 and 94 K in single crystals. In this temperature region, the Néel vector continuously rotates from the crystallographic $c$ axis (below 82 K) to the $a$ axis (above 94 K). The SRT allows for a temperature control of distinct antiferromagnetic states without the need for a magnetic field, making it apt for applications working at terahertz frequencies. For device applications, thin films of TFO are required as well as an electrical technique for read-out of the magnetic state. Here, we demonstrate that orthorhombic TFO thin films can be grown by pulsed laser deposition and the detection of the SRT in TFO thin films can be accessed by making use of the all-electrical spin Hall magnetoresistance, in good agreement for the temperature range where the SRT occurs in bulk crystals. Our results demonstrate that one can electrically detect the SRT in insulators.

Figure 1

(a) $2\mathrm{\Theta }/\omega$ scan of a 200-nm TFO thin film grown on a STO ${\left(001\right)}_p$ substrate measured out of plane. (b) $2\mathrm{\Theta }/\omega$ measured along the ${\left(112\right)}_p$ direction revealing both ${\left(024\right)}_o$ and ${\left(204\right)}_o$ TFO reflexes. (c) $\mathrm{\Phi }$ scans with $2\mathrm{\Theta }$ fixed at STO ${\left(011\right)}_p$ and TFO ${\left(112\right)}_o$ reflexes. (d) Relative orientation of the TFO unit cells (orange) with respect to the STO surface (blue). Both configurations are present across the sample surface. The cell dimensions are to scale showing a good fit of the TFO $b$ axis with the STO diagonal.

Figure 2

(a) Magnetization vs temperature for out-of-plane (oop, along the $c$ axis) and in-plane (ip, along the orthorhombic $a$ axis, ${45}^{\circ }$ towards the STO axis) configurations. The bulk spin reorientation transition is depicted in green. (b) Field sweep with field applied in the oop direction along the $c$ axis with a maximum applied field of 5 T. The data have been corrected for para- and diamagnetic background. (c) Top: XAS for linear horizontal (LH) and linear vertical (LV) polarization measured at 300 K. Bottom: XMLD spectrum calculated as the difference between LV and LH. (d) The magnetic configuration of the TFO unit cell above (left) and below (right) the spin reorientation transition drawn in vesta [24]. Due to the presence of two crystallographic domains the $a$ axis can be aligned in two directions leading to the magnetic configuration of the overall sample as sketched below corresponding to the cubic STO surface. The Néel N vector is shown in purple, and the canted moment M is shown in orange.

Figure 3

(a) Transverse spin Hall magnetoresistance (SMR) as a function of magnetic field at a temperature of 200 and 40 K. The field is applied in the $z$ direction (out of the plane). Note that the transverse SMR is extracted by subtracting the ordinary Hall effect from the measured transverse resistivity. A floating average has been applied with a range over 1 T to smooth the data. (b) Relative longitudinal resistivity measured simultaneously. (c) Sketch of the measurement configuration, with the coordinate system of the Hall bar indicated. (d) Amplitude of transverse and longitudinal relative resistivity at 10 T. The spin reorientation transition determined by SQUID measurements is depicted in green.

Figure 4

Atomic force microscopy image of the sample surface. The scale bar corresponds to $1\mu \mathrm{m}$.

Figure 5

Minor loop measured in SQUID in the out-of-plane configuration at different temperatures with a maximum applied field of 0.1 T. Note that the scale cannot be normalized because of the unknown volume of the soft-magnetic phase. The data have been corrected for para- and diamagnetic background.

Figure 6

Top: x-ray absorption spectra for circular polarized photons $\mathrm{C}+$ and $\mathrm{C}-$. Bottom: XMCD spectrum calculated as the difference between $\mathrm{C}+$ and $\mathrm{C}-$.

Figure 7

Temperature-dependent resistivity of the Pt Hall bar in the absence of a magnetic field.