Ising Spin Glass Fe0 Research Articles

Field Effects in the Ising Spin Glass Fe0.55Mn0.45TiO3

The temperature of onset of slow dynamics is determined from ac and dc susceptibility measurements under a magnetic bias fields for the Ising spin glass Fe0.55Mn0.45TiO3. Critical dynamics is found only in zero bias field while evidence for activated dynamics is found in strong magnetic fields. These results suggest the absence of a spin-glass phase transition in a magnetic field, in accordance with the droplet picture.

Spin glass behavior probed by various methods with different time- and space-scale of observation: Ising spin glass Fe 0.50 Mn 0.50 TiO 3

Under the expectation that the behavior of a spin glass (SG) system shows various aspects depending on the time- and space-scale of observations, we have studied the typical Ising spin glass Fe0.50Mn0.50TiO3 by measuring dc-magnetization, ac-susceptibility, Mossbauer spectrum, neutron scattering intensity and μ+SR time spectrum. We have demonstrated that the application of various methods with different time- and space-scale of observations to the same system is useful to clarify the property of the spin glass freezing, the Ising character and the de Almeida and Thouless-line.

No phase transition in a magnetic field in the ising spin glass Fe0.5Mn0.5TiO3.

The dynamic scaling behavior of the Ising spin glass F${\mathrm{e}}_{0.5}$M${\mathrm{n}}_{0.5}$Ti${\mathrm{O}}_{3}$ in superimposed dc magnetic fields has been studied. The dynamic freezing temperatures ${T}_{f}\left(\ensuremath{\omega},H\right)$ were determined as a function of field $0\ensuremath{\le}H\ensuremath{\le}3.1$ T and frequency $0.017\ensuremath{\le}\ensuremath{\omega}/2\ensuremath{\pi}\ensuremath{\le}5100$ Hz. The in-field scaling behavior is strikingly different from the zero-field behavior and is well described by activated dynamics and a correlation length that depends on field as $\ensuremath{\xi}\ensuremath{\propto}{H}^{\ensuremath{-}{\ensuremath{\nu}}_{H}}$. The results are in agreement with the droplet model predictions and strongly suggest that there is no phase transition in a magnetic field in 3D Ising spin glasses.

μ+SR study of Ising spin-glass Fe0.5Mn0.5TiO3

A typical Ising spin-glass Fe0.5Mn0.5TiO3 has been investigated by μ+ spin relaxation measurements. It is found that the local magnetic fields at the μ+ stopping sites appear at a temperature twice as high asTSG. The directional distribution of the local magnetic fields is nearly isotropic, indicating the existence of the transverse spin components. It is clearly demonstrated that the spins fluctuate belowTSG and even at ∼4 K. Taking into account the results obtained by other methods, the main part of the fluctuations is inferred to be due to the transverse spin components and the fluctuation limes at ∼4 K are driven into a range between ∼10−5 and ∼10−7 s.

Spin canting and hyperfine interactions in the reentrant Ising spin glass Fe0.62Mn0.38TiO3

The reentrant Ising spin glass Fe0.62Mn0.38TiO3 has been studied with Mossbauer spectroscopy as well as with field-cooled and zero-field-cooled magnetization measurements. The Neel and spin glass temperatures obtained are TN=32.8 K and Tg=25.8 K respectively. The 57Fe Mossbauer spectra recorded below 32 K are described in terms of two subspectra emanating from paramagnetic iron atoms and from iron atoms with canted magnetic moments. The canting angle was determined to be theta approximately=45 degrees for all temperatures below TN. The intensity of the paramagnetic subspectrum decreases with decreasing temperature and is typically about 25% at Tg. Longitudinal as well as transverse reentrant spin glass behaviour is observed in magnetization measurements.

Static and dynamic evidence for a transition at Tc = 0 in the Ising spin glass Fe0.3Mg0.7Cl2

The critical behaviour of the Ising spin glass Fe 0.3 Mg 0.7 Cl 2 has been studied by d.c. magnetisation, a.c. susceptibility and specific heat measurements. We have extended the range of our previous a.c. susceptibility measurements down to 0.02 Hz by using a new set up which utilises the possibilities of a 16 bit analog to digital converter. The relaxation time τ and the coefficients a 3 and a 5 of the non linear susceptibilities are powers of each other and diverge like exponential functions of θ/T. This confirms our former statement that Fe 0.3 Mg 0.7 Cl 2 is of a class different from that of traditional 3d systems and appears as an example of a real 2d Ising spin glass with T c =0. We claim that the essential L'etude du comportement critique du verre de spin Ising Fe 0.3 Mg 0.7 a ete realisee a l'aide de mesures d'aimantation, de susceptibilite alternative et de chaleur specifique. Les mesures de susceptibilite alternative ont ete effectuees jusqu'a de tres basses frequences (0.02Hz<f<3000Hz) grâce a la mise au point d'un dispositif experimental utilisant un convertisseur analogique numerique 16 bits rapide. Le temps de relaxation τ comme les coefficients a 3 et a 5 de la susceptibilite non lineaire sont puissances l'un de l'autre et divergent comme des exponentielles de θ/T. L'analyse des resultats confirme donc les conclusions d'une premiere etude du comportement critique dynamique : Fe 0.30 Mg 0.70 Cl 2 appartient a une classe d'universalite differente des systemes 3d et apparait comme exemple de verre de spin 2d Ising caracterise par une transition de phase a T c =0. Nous affirmons que les singularites observees apparaissent comme la limite naturelle a T c =0 des lois habituelles de «scaling». Nous nous differencions sur ce point des analyses presentees recemment pour d'autres systemes, ou un comportement semblable est interprete par une theorie ad hoc pour T c =0

Dynamic evidence for a 2d - 3d crossover in the Ising spin glass Fe0.35Mg0.65Br2

We report on magnetic dynamic properties in the ising spin glass Fe 0.35 Mg 0.65 Br 2 . The ac susceptibility curves have been deduced from direct susceptibility and Faraday rotation measurements over a wide frequency range extending from 100 kHz down to 0.05 Hz. The temperature dependence of the characteristic relaxation time cannot be fitted by either a power or an Arrhenius law over the whole frequency range Nous presentons une etude du comportement critique dynamique du verre de spin de type ising Fe 0,35 Mg 0,65 Br 2 . Les courbes de susceptibilites alternatives ont ete deduites de mesures directes et de mesures par effet Faraday sur une large gamme de frequence allant de 100 hKz a 0,05 Hz. La dependance en temperature du temps de relaxation caracteristique du systeme ne peut etre representee ni par une loi de puissance ni par une loi d'Arrhenius sur toute la gamme de frequence

DYNAMIC SCALING IN A SHORT RANGE ISING SPIN GLASS

Ac susceptibility data on the Ising spin glass Fe0.5Mn0.5TiO3 are analysed according to power law scaling and activated dynamic scaling. Both models are found to give a good scaling behaviour. However, the spin glass temperature achieved from activated dynamic scaling is significantly lower than the temperature for the field cooled susceptibility cusp