Spin glass behavior in the new amorphous alloys M2SnTe4 (M=Cr,Mn, Fe)

The amorphous alloys M₂SnTe₄ (M=Cr, Mn, Fe) are prepared by a new method involving the oxidation of main group polyanions (Zintl anions) by transition metal cations in solution at or below room temperature. The M₂SnTe₄ materials undergo a transition to a spin glass state at 12 K ? T_f ? 20 K and were characterized by dc magnetization, ⁵⁷Fe and ¹¹⁹Sn Mossbauer and x-ray diffraction measurements as well as the behavior of the remanent magnetization.     

Cluster phase transition in insulating spin glass Ga0.4Fe0.6NiAlO4

Mössbauer effect, a.c. susceptibility and magnetisation studies (4.2≦T≦350 K, ?20≦H≦20 kOe) show that in the mixed spined ferrite Ga_0.4Fe_0.6NiAlO₄, spin freezing occurs via cluster formation. As in some other insulating spin glasses, the spin glass phase diagram transitions occur not for individual spins but for clusters whose effective spins’ transverse and longitudinal components successively freeze. The presence of entropic spins and the centre shift of the field cooled hysteresis loop confirm the system’s frustrated nature.     

Magnetic relaxation phenomena in a CuMn spin glass

Experiments on the temperature and time dependence of the response function and the field cooled magnetisation of a Cu(Mn) spin glass at temperatures below the zero field spin glass temperature are used to explore the non-equilibrium nature of the underlying spin configuration. The results imply that a certain spin configuration is imprinted on the system as the temperature is decreased at a constant cooling rate. The cooling rate governs the magnitude of the FC magnetisation ((H,T)). Any intermittent halt at a constant temperature, , imprints an extended spin configuration, a process that is reflected e.g. in a downward relaxation of . On continued cooling at the same rate, the magnitude of (T) remains at a lower level than that of a continuous cooling curve. These results are put into the context of the corresponding behaviour of the response function as observed in measurements of the relaxation of the zero field cooled magnetisation. Received 27 October 1998 and Received in final form 30 November 1998     

Magnetic diffuse scattering in AgMn spin glass alloys

Magnetic diffuse peaks observed around the $\text{(1}\text{1}\text{2}\text{± δ 0)}$ type positions in reciprocal space have been studied in AgMn spin glass alloys by using neutron diffraction techniques. The position parameter δ of AgMn alloys coincides with that for CuMn alloys with the same Mn content even though the former has a larger lattice spacing than the latter by about 10%. The results suggest that the origin of the satellite diffuse peaks comes from a Fermi surface effect such as the RKKY interaction.     

The magnetic cluster blocking in Fe0.35V2O5 spin glass

The Wohlfarth method applied to the semiconducting spin glass Fe_0.35V₂O₅ indicates that the most intensive blocking of magnetic clusters occurs in low magnetic field at 7.5 K just below the temperature of the susceptibility maximum. However, the blocking process is diffused and several classes of clusters are blocked at higher temperatures.     

Cluster spin glass behaviour of mixed spinel ferrite Ga0.8Fe0.2NiCrO4

Mössbauer effect, d. c. magnetisation and a. c. susceptibility measurements in disordered spinel ferrite Ga_0.8Fe_0.2NiCrO₄ (0.3≦T≦300 K, ?12≦H (external field) ≦12 kOe) show it to be a cluster spin glass where Gabay-Toulouse phase diagram transitions occur not for individual spins but for groups of correlated spins (clusters) whose effective spin's transverse and longitudinal components successively freeze.     

Hyperfine splitting in the electron spin resonance of europium in SnTe

We observed hyperfine splitting of Eu in the highly degenerate semiconductor SnTe. The hyperfine coupling constant A(¹⁵¹Eu) = 29.0 Oe is compared with corresponding values for ¹⁵¹Eu in other host lattices.     

Spin-cluster effects and frustration in the uniaxial spin glass Fe2−xTi1+xO5

Transverse-field (TF) muon-spin-relaxation (μSR) and Mössbauer experiments on the uniaxial insulating spin glass Fe_2?xTi_1+xO₅ (x=0.25) have been performed near and below the spin-glass temperature (T _g). The effect of a transverse field on the spin-freezing process and spin-glass state has been investigated by measuring the field-and temperature-dependencies of the μSR parameters. Spin-cluster effects signaled by anomalous μ-spin relaxation have been observed in a temperature region just aboveT _g. An interpretation supported by recently developed theoretical models addressing non-linear relaxation in an intermediate Griffiths phase is offered.     

Photo-induced phase transitions probed by X-ray absorption spectroscopy: Fe(II) spin crossover complex

Photo-induced phase transitions in spin-crossover complex [Fe(II)(2-pic)₃]Cl₂EtOH were investigated by X-ray absorption spectroscopy (XAS) technique. In situ XAS results showed that the metal-ligand (Fe–N) bond distance expands by ca. 0.20 Å upon photo-induced (S=0→S=2) spin conversion. We find that nearly octahedral (O_h) symmetry of FeN₆ coordination remains in the photo-induced high spin state. The next-nearest neighbor Fe–C radial distribution shows a subtle change due to local distortions of ligand molecules. Inhomogeneous distribution of strains may disturb cooperative photo-induced phase transitions removing centers of inversion symmetry.     

Observation of spin glass transition in spinel LiCoMnO_4

Spinel Li CoMnO4 is prepared by solid-state reaction and its magnetic properties are comprehensively studied by direct current(DC) and alternating current(AC) susceptibilities, isothermal remanent magnetizations, and magnetic hysteresis.Fitting to the Curie–Weiss law by using high-temperature zero-field-cooled susceptibility confirms a low-spin state of Co3+with S = 0. Both the fitting parameters first increase and then tend to be saturated at high magnetic fields through using isothermal remanent magnetizations, which suggests a spin glass transition at low temperature. AC susceptibility study also supports this conclusion since the frequency dependence of peak position and intensity follows the tendency of a spin glass transition. The origin of the spin-glass transition in Li CoMnO4 might be attributed to a spatial segregation between non-magnetic Co3+regions and spin glass ordered regions of Mn4+ions.     

Mössbauer studies of FeAl2O4 and FeIn2S4 spin glass spinels

Mössbauer experiments were performed on iron spinels in which spin-glass-like properties are observed. The spin glass character of FeIn₂S₄ cannot be considered as canonical due to the existence of a relaxation-time distribution nearT _g. A surprising first-order transition atT _g has been evidenced for FeAl₂O₄.     

正交LiMnO2中的重入自旋玻璃行为

用水热技术合成了单相正交LiMnO2(o-LiMnO2)粉末,X射线衍射表明其空间群为Pmnm.X射线衍射精修结果指出该材料存在少量的阳离子无序,但这种无序对材料的磁性没有表现出明显的影响.静态和动态的磁性研究结果表明o-LiMnO2中存在重入自旋玻璃行为,即在T≤TC≈118 K,反铁磁态转向铁磁态,在T≤Tf≈50 K,铁磁态又转向自旋倾斜玻璃态.     

Impurity induced Fe spin reorientation in CeFe2

CeFe₂ in a unique ferromagnetic system in which small nonmagnetic substitutions on the Fe sublattice induces a second transition into a state of near zero net magnetization (presumably in a antiferromagnetic state). The second transition can be suppressed and ferromagnetism restored by substitution of (10%) Y at the Ce site.     

Local magnetization of Co andMn impurities in the reentrant spin glass Au0.82Fe0.18

The low-temperature nuclear orientation technique has been used to study the magnetic behaviour of⁶⁰Co and⁵⁴Mn impurity atoms in the reentrant spin glass Au_0.82Fe_0.18. The results obtained for⁶⁰Co indicate that Co moments follow the distribution of Fe directions. In contrast, Mn moments show a spread directional distribution. These results are the consequence of the different character of Mn-Fe andFe-Fe interactions at short distances.     

Magnetic and Mössbauer data of Fe in K2ZnF4, analyzed in the spin Hamiltonian formalism

Magnetic measurements on single crystals and Mössbauer spectra of powders under magnetic field, recorded on Fe²⁺ doped K₂ZnF₄, have been analyzed in the spin Hamiltonian formalism. The data slightly depart from the expectations of a spin 2 in D_4h symmetry. The occurrence of vibronic effects is discussed.