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Spin dynamics in copper metaborate studied by muon spin relaxation
Copper metaborate CuBO was studied by muon spin relaxation
measurements in order to clarify its static and dynamic magnetic properties.
The time spectra of muon spin depolarization suggest that the local fields at
the muon site contain both static and fluctuating components in all ordered
phases down to 0.3 K. In the weak ferromagnetic phase (20 K~~9.3 K), the
static component is dominant. On the other hand, upon cooling the fluctuating
component becomes dominant in the incommensurate helix phase (9.3K > T > 1.4K).
The dynamical fluctuations of the local fields persist down to 0.3K, where a
new incommensurate phase (T < 1.4K) is expected to appear. This result suggests
that spins fluctuate even at T \to 0. We propose two possible origins of the
remnant dynamical spin fluctuations: frustration of the exchange interactions
and the dynamic behavior of the soliton lattice
Electronic and magnetic properties of substitutional Mn clusters in (Ga,Mn)As
The magnetization and hole distribution of Mn clusters in (Ga,Mn)As are
investigated by all-electron total energy calculations using the projector
augmented wave method within the density-functional formalism. It is found that
the energetically most favorable clusters consist of Mn atoms surrounding one
center As atom. As the Mn cluster grows the hole band at the Fermi level splits
increasingly and the hole distribution gets increasingly localized at the
center As atom. The hole distribution at large distances from the cluster does
not depend significantly on the cluster size. As a consequence, the spin-flip
energy differences of distant clusters are essentially independent of the
cluster size. The Curie temperature is estimated directly from these
spin-flip energies in the mean field approximation. When clusters are present
estimated values are around 250 K independent of Mn concentration whereas
for a uniform Mn distribution we estimate a of about 600 K.Comment: 7 pages, 5 figures, 2 tables; Revised manuscript 26. May 200
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