We have considered the two-spin interaction spherical spin-glass model with asymmet-ric bonds (coupling constants). Besides the usual interactions between spins and bonds and between the spins and a thermostat with temperature T σ there is also an additional factor: the bonds are not assumed random a priori but interact with some other thermostat at the temperature T J. We show that when the bo...

– We introduce a finite-connectivity ferromagnetic model with a three-spin interaction which has a crystalline (ferromagnetic) phase as well as a glass phase. The model is not frustrated, it has a ferromagnetic equilibrium phase at low temperature which is not reached dynamically in a quench from the high-temperature phase. Instead it shows a glass transition which can be studied in detail by a...

We generalize the strategy, we recently introduced to prove the existence of the thermodynamic limit for the Sherrington-Kirkpatrick and p-spin models, to a wider class of mean field spin glass systems, including models with multi-component and non-Ising type spins, mean field spin glasses with an additional Curie-Weiss interaction, and systems consisting of several replicas of the spin glass m...

The Ising spin glass in a transverse field. Results of two fermionic models. Abstract We analyze the long range Ising spin glass in a transverse field Γ by using Grassmann variables in a field theory where the spin operators are represented by bilinear combinations of fermionic fields. We compare the results of two fermionic models. In the four state (4S)-model the diagonal S z i operator has t...

We introduce an effective field theory for the vicinity of a zero temperature quantum transition between a metallic spin glass (“spin density glass”) and a metallic quantum paramagnet. Following a mean field analysis, we perform a perturbative renormalization-group study and find that the critical properties are dominated by static disorder-induced fluctuations, and that dynamic quantum-mechani...

Recent neutron diffraction and NMR studies suggest that the incommensurately modulated spin cycloid structure of BiFeO3 is stable down to 4.2 K, whereas DC [M(T)] and AC [χ (ω, T)] magnetization, and caloric studies have revealed several magnetic transitions including a spin glass transition around 25 K. The two sets of observations are irreconcilable and to settle this, it is important to firs...

We report a study of the low temperature bulk magnetic properties of the spin ice compound Dy2Ti2O7 with particular attention to the (T,4 K) spin freezing transition. While this transition is superficially similar to that in a spin glass, there are important qualitative differences from spin glass behavior: the freezing temperature increases slightly with applied magnetic field, and the distrib...

– We compare slow domain growth aging in a disordered ferromagnet and aging in a spin glass, by studying the different phases of a reentrant system. We measure the relaxation of the low-frequency ac susceptibility χ, in both the ferromagnetic and spin-glass phases of a CdCr1.9In0.1S4 sample. A restart of aging processes when the temperature is lowered ('chaos' effect) is observed in both phases...