Muons and magnets

Abstract:

Wepresent the synthesis, single-crystal X-ray (173 K) and powder neutron (2-30 K) structures and its thermal, optical and magnetic properties of K 2Co^II 3(OH)2(SO4) 2(H2O)2. It is a ferrimagnet (TC= 29.7 K) constructed of Co3(OH)2 diamond chains connected by sulfate and it displays hysteresis loops ranging from being soft with nearly zero coercivity between 29 and 10 K to very hard reaching coercive field exceeding 70 kOe at 1.8 K. This dramatic change is associated with the changes in domain shape due to the strong exchange anisotropy. Considerable frequency dependence of the acsusceptibilities is observed in the ordered state.Measurements on a single crystal have established the magnetic axes to be a-axis (easy), b-axis (intermediate), and c-axis (hard). © 2010 American Chemical Society.

Abstract:

We present the results of muon-spin relaxation and heat capacity measurements on LiFeSi2O6 and NaFeSi2O 6. In synthetic samples of both compounds we see a single muon oscillation frequency consistent with commensurate magnetic structures below TN. In contrast, for a specimen of naturally occurring NaFeSi2O 6, in which multiferroicity has been observed, a rapid Gaussian depolarization of the muon polarization is observed instead, showing that the magnetic structure in this case is more complex. Heat capacity measurements reproduce the phase diagrams previously derived from other techniques and demonstrate that the main contribution to the magnetic entropy is associated with the buildup of correlations in the quasi-one-dimensional Fe³⁺ chains. © 2010 The American Physical Society.