Figure 2

Left panel: ESR spectra of the crystal with a 44 K SC phase, divided into three temperature ranges: (a) 300 to 50 K, (b) 45 to 35 K and (c) 30 to 1.8 K.

The central panel: (d), (e) and (f), show ESR spectra for the crystal without 44 K SC phase in the same temperature ranges. The sharp signal at zero field in (c) and (f) is an indication of Meissner state and the upward or downward curvature is caused simply by microwave measurement phase. Note that the signal level in (c) and (f) is one order of magnitude higher than that in (b). The right panel shows the fitting for 44K-phase using different absorption mechanisms: (g) Lorentzian fitting for antiferromagnetic resonance absorption (AFMR). The insert shows the temperature dependence of the fitting resonance fields and widths, which completely contradicts to a typical AMFR (See the text); (h) Non-resonant absorption in a normal conducting state (NS); (i) Non-resonant absorption in a superconducting state (SC). The insert shows that H_c1 taken at the spectral dip follows an approximate square-root behavior (red line).