Muon spin relaxation studies of the frustrated quasi-two-dimensional square-lattice spin system Cu(Cl,Br)La(Nb,Ta)2O7 : Evolution from spin-gap to antiferromagnetic state
Abstract
We report muon spin relaxation (μSR) and magnetic-susceptibility measurements on Cu(Cl,Br)La(Nb,Ta)2O7 , which demonstrate: (a) the absence of static magnetism in (CuCl)LaNb2O7 down to 15 mK confirming a spin-gapped ground state; (b) phase separation between partial volumes with a spin-gap and static magnetism in (CuCl)La(Nb,Ta)2O7 ; (c) history-dependent magnetization in the (Nb,Ta) and (Cl,Br) substitution systems; (d) a uniform long-range collinear antiferromagnetic state in (CuBr)LaNb2O7 ; and (e) a decrease in Néel temperature with decreasing Br concentration x in Cu(Cl1-xBrx)LaNb2O7 with no change in the ordered Cu moment size for 0.33≤x≤1 . Together with several other μSR studies of quantum phase transitions in geometrically frustrated spin systems, the present results reveal that the evolution from a spin-gap to a magnetically ordered state is often associated with phase separation and/or a first-order phase transition.
- Publication:
-
Physical Review B
- Pub Date:
- November 2009
- DOI:
- 10.1103/PhysRevB.80.174408
- arXiv:
- arXiv:0806.2021
- Bibcode:
- 2009PhRvB..80q4408U
- Keywords:
-
- 75.30.Kz;
- 73.43.Nq;
- 76.75.+i;
- Magnetic phase boundaries;
- Quantum phase transitions;
- Muon spin rotation and relaxation;
- Condensed Matter - Strongly Correlated Electrons;
- Condensed Matter - Superconductivity
- E-Print:
- 10 pages 10 color figures