Muons and magnets

Abstract:

Muon spin relaxation measurements are reported on samples of dimethylammonium metal formates containing magnetic divalent nickel, cobalt, manganese, and copper ions. These hybrid organic-inorganic perovskites exhibit weak ferromagnetism and are, apart from the copper system, multiferroics with well-separated magnetic and antiferroelectric transitions. We use muons to follow the sublattice magnetization, observing the effect of the spin reorientation transitions below TN and the criticality approaching TN. The multiferroic samples have three-dimensional antiferromagnetic interactions but the copper sample shows quasi-one-dimensional behavior due to its Jahn-Teller distorted structure with a ratio of its interchain and intrachain exchange constants | J′ /J | ≃0.037. © 2010 The American Physical Society.

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.