790 research outputs found
Antisite Disorder-induced Exchange Bias Effect in Multiferroic Y2CoMnO6
Exchange bias effect in the ferromagnetic double perovskite compound
YCoMnO, which is also a multiferroic, is reported. The exchange bias,
observed below 8~K, is explained as arising due to the interface effect between
the ferromagnetic and antiferromagnetic clusters created by {\it antisite}
disorder in this material. Below 8~K, prominent ferromagnetic hysteresis with
metamagnetic "steps" and significant coercive field, 10~kOe are
observed in this compound which has a 75~K. A model based on
growth of ferromagnetic domains overcoming the elastic energy of structurally
pinned magnetic interfaces, which closely resembles martensitic-like
transitions, is adapted to explain the observed effects. The role of {\it
antisite} disorder in creating the domain structure leading to exchange bias
effect is highlighted in the present work.Comment: 4 pages two-column, 4 figures, accepted to Appl. Phys. Let
Spin Freezing in the Spin Liquid Compound FeAl2O4
Spin freezing in the -site spinel FeAlO which is a spin liquid
candidate is studied using remnant magnetization and nonlinear magnetic
susceptibility and isofield cooling and heating protocols. The remnant
magnetization behavior of FeAlO differs significantly from that of a
canonical spin glass which is also supported by analysis of the nonlinear
magnetic susceptibility term . Through the power-law analysis of
, a spin-freezing temperature, = 11.40.9~K and critical
exponent, = 1.480.59 are obtained. Cole-Cole analysis of magnetic
susceptibility shows the presence of broad spin relaxation times in
FeAlO, however, the irreversible dc susceptibility plot discourages an
interpretation based on conventional spin glass features. The magnetization
measured using the cooling-and-heating-in-unequal-fields protocol brings more
insight to the magnetic nature of this frustrated magnet and reveals
unconventional glassy behaviour. Combining our results, we arrive at the
conclusion that the present sample of FeAlO consists of a majority spin
liquid phase with "glassy" regions embedded.Comment: 5 pages, 6 figs, 2-column, Accepted to Phys. Rev.
Double-phase transition and giant positive magnetoresistance in the quasi-skutterudite GdIrSn
The magnetic, thermodynamic and electrical/thermal transport properties of
the caged-structure quasi-skutterudite GdIrSn are
re-investigated. The magnetization , specific heat and the
resistivity reveal a double-phase transition -- at 10~K
and at 8.8~K -- which was not observed in the previous report on
this compound. The antiferromagnetic transition is also visible in the thermal
transport data, thereby suggesting a close connection between the electronic
and lattice degrees of freedom in this Sn-based quasi-skutterudite. The
temperature dependence of is analyzed in terms of a power-law for
resistivity pertinent to Fermi liquid picture. Giant, positive
magnetoresistance (MR) 80 is observed in GdIrSn at
2~K with the application of 9~T. The giant MR and the double magnetic
transition can be attributed to the quasi-cages and layered antiferromagnetic
structure of GdIrSn vulnerable to structural distortions and/or
dipolar or spin-reorientation effects. The giant value of MR observed in this
class of 3:4:13 type alloys, especially in a Gd-compound, is the highlight of
this work.Comment: 20 pages single column, 7 figures, 1 table; Accepted to J. Appl.
Phys., 201
The student voice as contributor to quality education through institutional design
The inclusion of students’ voices in different aspects of quality has evolved over the years. Consequently, students take on different roles – ranging from providing feedback on their educational experiences, to actively participating or even leading change initiatives. In making claims for different ways of conceptualising or including students’ voices, the literature often criticises some forms of engagement with student voices in favour of another. This article is based on the premise that the complexity of quality outcomes in higher education needs to be complemented by a variety of inputs from students. By drawing from examples of two high-impact practices from the University of the Free State, the article further argues for using different forms of student voices to inform how we design institutional support structures to ultimately enhance the quality of students’ educational experiences. At its core, this cyclical interaction between students’ voices and institutional design revolves around evidence – thereby contributing to the quality of educational outcomes, and ultimately students’ success
Quantum Quenches in a Holographic Kondo Model
We study non-equilibrium dynamics and quantum quenches in a recent
gauge/gravity duality model for a strongly coupled system interacting with a
magnetic impurity with spin. At large , it is convenient to write
the impurity spin as a bilinear in Abrikosov fermions. The model describes an
RG flow triggered by the marginally relevant Kondo operator. There is a phase
transition at a critical temperature, below which an operator condenses which
involves both an electron and an Abrikosov fermion field. This corresponds to a
holographic superconductor in AdS and models the impurity screening. We
study the time dependence of the condensate induced by quenches of the Kondo
coupling. The timescale for equilibration is generically given by the
lowest-lying quasinormal mode of the dual gravity model. This mode also governs
the formation of the screening cloud, which is obtained as the decrease of
impurity degrees of freedom with time. In the condensed phase, the leading
quasinormal mode is imaginary and the relaxation of the condensate is
over-damped. For quenches whose final state is close to the critical point of
the large phase transition, we study the critical slowing down and obtain
the combination of critical exponents . When the final state is exactly
at the phase transition, we find that the exponential ringing of the
quasinormal modes is replaced by a power-law behaviour of the form . This indicates the emergence of a discrete scale
invariance.Comment: 23 pages + appendices, 11 figure
Field tuned critical fluctuations in YFe2Al10: Evidence from magnetization, 27Al (NMR, NQR) investigations
We report magnetization, specific heat, and NMR investigations on YFe2Al10
over a wide range in temperature and magnetic field and zero field (NQR)
measurements. Magnetic susceptibility, specific heat and spin-lattice
relaxation rate divided by T (1/T1T) follow a weak power law (T^-0.4)
temperature dependence, which is a signature of critical fluctuations of Fe
moments. The value of the Sommerfeld-Wilson ratio and linear relation between
1/T1T and chi(T) suggest the existence of ferromagnetic correlations in this
system. No magnetic ordering down to 50 mK in Cp(T) and the unusual temperature
and field scaling of the bulk and NMR data are associated with a magnetic
instability which drives the system to quantum criticality. The magnetic
properties of the system are tuned by field wherein ferromagnetic fluctuations
are suppressed and a crossover from quantum critical to FL behavior is observed
with increasing magnetic field
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