Figure2a.dat contains the data shown in Figure 2(a). The file is made up of 2 pairs of columns titled: Xperp and Yperp; Xpara and Ypara. These represent the Magnetic Field (X) and ESR signal (Y) data taken at 240 gigahertz at perpendicular and parallel orientations, respectively.

Figure2b.dat contains the data shown in Figure 2(b). The file is made up of 2 pairs of columns titled: Xwidth and Ywidth; Xg and Yg. Xwidth and Ywidth are the orientation (X) and the ESR signal width (Y), respectively. Xg and Yg are the orientation (X) and the ESR signal g factor (Y), respectively.

Figure2c.dat contains the data shown in Figure 2(c). The file is made up of 5 pairs of columns titled: X20 and  Y20; X10 and Y10; X4 and Y4; X2p4 and Y2p4;     X1p4 and Y1p4. These represent the Magnetic Field (X) and ESR signal (Y) data taken at 73 gigahertz at 20, 10, 4, 2.4 and 1.4 kelvin, respectively.

Figure2d.dat contains the data shown in Figure 2(d). The file is made up of 6 pairs of columns titled: Xa and Ya; Xb and Yb; Xc and Yc; Xd and Yd; Xe and Ye; Xf and Yf. These represent the Magnetic Field (X) and ESR freqeuncy (Y) for resonance a, b, c, d, e and f, respectively.

Figure2e.dat contains the data shown in Figure 2(e). The file is made up of 1 pairs of columns titled: Xsusceptibility and YSusceptibility. They present the orientation (X) ad low-temperature susceptibility tail (Y), respectively.

Figure2e_inset.dat contains the data shown in the inset to Figure 2(e). The file is made up of 2 pairs of columns titled: X00 and Y00; X90 and Y90. These represent the Temperature (X) and Susceptibility (Y) data taken at parallel and perpendicular orientations, respectively.

FigureS3a.dat contains the data shown in Figure S3(a). The file is made up of 16 pairs of columns titled: X45p807 and Y45p807; X46p548 and Y46p548; X52p686 and Y52p686; X56p359 and Y56p359; X59p397 and Y59p397; X63p054 and Y63p054; X69p048 and     Y69p048; X71p839 and Y71p839; X72p992 and Y72p992; X87p457 and Y87p457; X95p728 and     Y95p728; X108p133 and Y108p133; X120p074 and Y120p074; X137p195 and Y137p195; X153p64 and Y153p64; X160p48 and Y160p48. These represent the Magnetic Field (X) and ESR signal (Y) data taken at 1.4 kelvin at 45.807,   46.548, 52.686, 56.359, 59.397, 63.054, 69.048, 71.839, 72.992, 87p457, 95p728, 108.133, 120.074, 137p195, 153.64 and 160.48 gigahertz respectively.