Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Li, B.
no journal, ,
Negative thermal expansion is usually realized at the ferromagnetic or antiferromagnetic ordering transitions as magnetoelastic responses, where the spontaneous magnetostriction counteracts the normal lattice contraction. Here, our in-situ neutron diffraction study on hexagonal Lave phase (P63/mmc) Hf0.86Ta0.14Fe2 reveals that larger lattice expansion can be induced by a first-order isostructural transition to collinear ferromagnetic state from geometrically frustrated k = 0 Kagome antiferromagnet with 120 deg configuration of magnetic moments of Fe ions. The magnetic frustration manifests itself as well-recued magnetic moment 
0.6 muB and facilitates the competition and interplay of lattice and magnetic degrees of freedom. The energy gain ( 4 meV) originating from lattice expansion turns out to drive the transition with relief of magnetic frustration, supported by the first-principle total energy calculations. Our work points out a novel routine to negative thermal expansion in the magnetic order to order transition assisted by magnetic frustration.
川北 至信; 田原 周太*
no journal, ,
There are many superionic conductors among Ag- and Cu-based compounds where Ag or Cu ions migrate into interstices of crystalline lattice. Mobile ions usually show large fluctuations in their distribution which easily exceed unit cell. Even in the molten state, we found that Ag-Ag (Cu-Cu) partial structure shows nano-order fluctuation. Quasi-elastic neutron scattering of molten CuI and the following mode distribution analysis revealed that there exist three kinds of relaxation mode which are slow diffusion of I, ten times faster diffusion of Cu and very quick local vibrational mode of Cu in a cage formed by surrounding I ions. Molecular dynamic simulation with polarizable ion model also confirms that Cu shows two types of motion. We will discuss how the nano-order fluctuations in Ag (Cu) distribution relate to the emergence of superionic phase.