Temperature-dependent electron spin resonance (ESR) measurements of two low-dimensional quantum spin systems, the 5 = 1/2 spin-ladder system Cu2(1,4-diazacycloheptane)2Cl4 (Cu2(C5H12N2)2Cl 4) and the gapless S = 1 bond-alternating one-dimensional antiferromagnet trans-Ni(333-tet)(N3)(ClO4), have been performed. X-band electron spin resonance (ESR) measurements of single-crystal Cu2(C5H12N2)2Cl 4 show the increase of linewidth and anisotropic g-shifts below 8 K similar to those known for one-dimensional antiferromagnet. On the other hand, Ni(333-tet)(N3)(ClO4) has broad line-width and ESR has been observed for the first time by our high-field ESR. Its linewidth increases as the temperature is decreased, while the g-shift seems to be isotropic and the g-value decreases as the temperature is decreased. This g-shift can be connected to the quantum fluctuation of the system.
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