Low-temperature magnetic fluctuations in the Kondo insulator ${\mathrm{SmB}}_6$

We present the results of a systematic investigation of the magnetic properties of the three-dimensional Kondo topological insulator ${\mathrm{SmB}}_6$ using magnetization and muon-spin relaxation/rotation ($\mu$SR) measurements. The $\mu$SR measurements exhibit magnetic field fluctuations in ${\mathrm{SmB}}_6$ below $\sim 15$ K due to electronic moments present in the system. However, no evidence for magnetic ordering is found down to 19 mK. The observed magnetism in ${\mathrm{SmB}}_6$ is homogeneous in nature throughout the full volume of the sample. Bulk magnetization measurements on the same sample show consistent behavior. The agreement between $\mu$SR, magnetization, and NMR results strongly indicate the appearance of intrinsic bulk magnetic in-gap states associated with fluctuating magnetic fields in ${\mathrm{SmB}}_6$ at low temperature.

Figure 1

Temperature dependence of the magnetic susceptibility of ${\mathrm{SmB}}_6$, measured under ZFC and FC conditions in an applied field of 70 kOe. Inset shows the full $M\left(H\right)$ loop of ${\mathrm{SmB}}_6$, measured at 1.8 K.

Figure 2

(a) ZF-$\mu$SR asymmetry signals of ${\mathrm{SmB}}_6$, collected at different temperatures for Sample A. The solid lines are fits to the data using Eq. (3). (b) Temperature dependence of the muon-spin relaxation rate $\lambda$ due to the presence of electronic moments in ${\mathrm{SmB}}_6$. The inset shows the $\lambda \left(T\right)$ of sample A in logarithmic scale.

Figure 3

(a) The wTF-$\mu$SR asymmetries, collected at different temperatures for sample B in a wTF of 50 Oe. (b) The temperature dependence of $\lambda$ of ${\mathrm{SmB}}_6$, collected from the wTF-$\mu$SR data.

Figure 4

Asymmetry signals under different applied longitudinal fields, collected at (a) 1.8 K and (b) 50 K. The solid lines are the fits to the data using Eq. (5).

Figure 5

Field dependence of $\lambda$ for (a) 1.8 K and (b) 50 K, showing the LCR peaks at around 40 Oe for both temperatures. The solid lines are a guide to the eye. The inset in Fig. 5 shows the field dependence of $\lambda$ up to 1000 Oe.