Extended Data Figure 2: Temperature and magnetic-field dependence of magnetization at low temperatures.

a, Temperature dependence of magnetization M/B under magnetic fields up to B = 14 T for the sample used in the specific heat measurements shown in Fig. 4. The Curie-like contribution that is absent in K(T) is clearly seen, originating from magnetic defects. The dashed line represents a power-law behaviour with T^−1/2 dependence. The susceptibility in the low-field limit appears to follow the T^−1/2 dependence better than the conventional Curie–Weiss dependence. At very low temperatures, the Curie-like contribution becomes independent of T for high B fields, implying the saturation of moment from magnetic defects. In the inset, M(T) at B = 7.0 T (green line) is compared with that calculated by integrating ∂M(T, B)/∂T, which we obtained from S(T, B) using the Maxwell relation (red pluses). b, M(B)–B curves at low temperatures. From the offset from the linear magnetization at high fields, we estimate the saturation moment that originates from magnetic defects to be 0.022μ_B (as indicated by the arrow). This corresponds to 2% of the magnetic defects with g = 2 and a S = 1/2 moment. The Zeeman gap in the density-of-states model in Fig. 4 is 2αμ_BB with α = 2.9, suggesting a g-factor of 5.8 for the moment that comes from the magnetic defects. Incorporating g = 5.8, the best estimate of the number of magnetic defects with S = 1/2 moments is 0.8%. This estimate is consistent with the estimate from the specific heat in Fig. 4, which indicates an entropy S(T) of 1%–2% of Rln(2) at T = 5 K, where R is the gas constant. c, B^1/2 × ∂M(T,B)/∂T shows a scaling with T/B similar to that for C and T₁, indicating that the three probes capture the same excitations.