We present transverse field muon spin rotation/relaxation measurements on single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find that the spins are more easily polarized when the field is perpendicular to the kagome plane. We
demonstrate that the difference in magnetization between the different directions cannot be accounted for by Dzyaloshinksii-Moriya type interactions alone, and that anisotropic axial interaction is present.
Using muon spin resonance we examine the organometallic hybrid compound Cu(1,3-benzenedicarboxylate) [Cu(1,3-bdc)], which has structurally perfect spin 1/2 copper kagome planes separated by pure organic linkers. This compound has antiferromagnetic in
teractions with Curie-Weiss temperature of -33 K. We found slowing down of spin fluctuations starting at T=1.8 K, and that the state at T->0 is quasi-static with no long-range order and extremely slow spin fluctuations at a rate of 3.6 1/usec. This indicates that Cu(1,3-bdc) behaves as expected from a kagome magnet and could serve as a model kagome compound.
A proper understanding of the mechanism for cuprate superconductivity can emerge only by comparing materials in which physical parameters vary one at a time. Here we present a variety of bulk, resonance, and scattering measurements on the (Ca_xLa_{1-
x})(Ba_{1.75-x}La_{0.25+x})Cu_3O_y high temperature superconductors, in which this can be done. We determine the superconducting, Neel, glass, and pseudopage critical temperatures. In addition, we clarify which physical parameter varies, and, equally important, which does not, with each chemical modification. This allows us to demonstrate that a single energy scale, set by the superexchange interaction J, controls all the critical temperatures of the system. J, in-turn, is determined by the in plane Cu-O-Cu buckling angle.
We present magnetization measurements on oriented powder of ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ along and perpendicular to the orienting field. We find a dramatic difference in the magnetization between the two directions. It is biggest at low measurement f
ields $H$ or high temperatures. We show that the difference at high temperatures must emerge from Ising-like exchange anisotropy. This allows us to explain muon spin rotation data at $Tto 0$ in terms of an exotic ferromagnetic ground state.
We investigate the cross-over temperature T* as a function of doping in (Ca_{x}La_{1-x})(Ba_{1.75-x}La_{0.25+x})Cu_3O_{y}, where the maximum Tc (Tc^max) varies continuously by 30% between families (x) with minimal structural changes. T* is determined
by DC-susceptibility measurements. We find that T* scales with the maximum Neel temperature TN^max of each family. This result strongly supports a magnetic origin of T*, and indicates that three dimensional interactions play a role in its magnitude.
