Magnetism and a field-cycling induced effect in staircase Kagomé antiferromagnet PbCu$_3$TeO$_7$ revealed by NMR

Abstract

We report $^{125}$Te and $^{63,65}$Cu nuclear magnetic resonance (NMR) studies on single crystals of staircase Kagomé antiferromagnet PbCu3TeO7 ($T_{N1}\approx$ 36 K). A Curie constant as large as $Θ$~140 K is obtained by a Curie-Weiss fitting of the high-temperature Knight shift. The frustration factor f (= $Θ/T_N $)$\approx$ 4 implies intermediate frustration in this system. From the high-temperature Knight shift data of $^{125}$Te, its hyperfine coupling constant is estimated to be $^{125}A_{hf}$ = -67 kOe/$μ_B$, which suggests a strong interlayer coupling bridging the neighboring Kagomé layers. At $T$= 2 K, we find two types of zero-field NMR signals. One has no dependence on the history of the field treatment, which is consistent with Cu NMR signals from inequivalent Cu sites with different internal hyperfine fields. The other one is only seen after a field-cycling process, which is consistent with domain wall contributions in this frustrated antiferromagnet.

Revised argument