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1.
Experimental results on EuxSr1?xS provide clear evidence for a cooperative phenomenon at the spin-glass transition, as distinguished from ordinary thermal blocking of superparamagnetic clusters. Only below the percolation threshold xp = 0.13 can single-clusters aspects be separated clearly (superparamagnetic regime). In the spin-glass regime for x >xp, susceptibility and remanent magnetization are studied near the freezing temperature in dependence on temperature, magnetic field and observation time. The anomalous slow relaxations of the remanent magnetization, which follow a power-law, exhibit a strong variation just near Tf0, the transition temperature deduced from static magnetization measurements. In addition, Tf values derived from ac-χ measurements are distinctly frequency dependent; the frequency variation decreases towards low frequencies and seems to saturate near the Tf0 value. The strong sensitivity of χ(Tf) to even small applied fields can be represented by a universal function independent of concentration. All these results emphasize the importance of the interactions among the spin clusters of spin glasses which are partially frustrated.  相似文献   

2.
Transverse-field (TF) muon-spin-relaxation (μSR) and Mössbauer experiments on the uniaxial insulating spin glass Fe2?xTi1+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.  相似文献   

3.
In a weak magnetic field LaMnO3+δ exhibits at δ=0.065 below the paramagnetic-to-ferromagnetic (FM) Curie temperature, TC, a mixed (spin-glass and FM) phase followed by a frustrated FM phase at δ between 0.100 and 0.154. The same behavior is observed in La1−xCaxMnO3 with x between 0 and 0.3. This can be understood by the similar variation of the Mn4+ concentration, c between ≈0.13 and 0.34, in both materials when x or δ is increased. On the other hand, considerable differences are found between these compounds in the values of the magnetic irreversibility, in the dependencies of TC(c) and the magnetic susceptibility, χ(c), as well as in the critical behavior of χ(T) near TC. These differences can be explained by distortions of the cubic perovskite structure, by the reduced lattice disorder and by the more homogeneous hole distribution in LaMnO3+δ than in La1−xCaxMnO3.  相似文献   

4.
Mössbauer absorption spectra habe been obtained as a function of temperature for Cr1?xFex alloys with x=0.15, 0.18, 0.20, 0.22, 0.25 and 0.30. For the specimens near the critical composition of ferro-antiferromagnetic transition (about 18 at % Fe), abrupt increase of the average hyperfine field was found at the temperature Tf which is far below the ferromagnetic Curie temperature. The observed hyperfine field distribution P(H) consists of two peaks centered around zero and finite hyperfine field (low field peak and high field peak), indicating the coexistence of paramagnetic-like and ferromagnetic moments. Below Tf, the intensity fraction and the maximum position of the high field peak curve increase more rapidly than in the ferromagnetic temperature range, while its halfwidth decreases suddenly. These facts are interpreted as due to the freezing of spins by reentering into the spin-glass phase.  相似文献   

5.
We report the results of our investigation in CeNi2−xCuxSn2 (x=0, 0.4, 1.0, 1.6 and 2.0), a new pseudoternary series with CaBe2Ge2-type tetragonal structure. Substitution of Cu for Ni leads to a linear increase in the constants a, c and the unit cell volume v. As probed by the low temperature dependence of ac susceptibility χac(T), the Tf temperature, which corresponds to the freezing temperature of the spin-glass clusters, is annihilated above 2.0 K significantly for the samples with x≥1.6. This observation proves conclusively that the Ni-rich samples in the series CeNi2−xCuxSn2 have the advantage of forming the spin-glass-like state.  相似文献   

6.
《Physics letters. A》1998,244(5):437-441
The transition to the spin-glass phase at T = 0 has been found for a two-dimensional ensemble of amphoteric impurities with charge transfer. The characteristics of the charge clustering found in specimens at low temperatures have been investigated. The finite size scaling with the critical exponents v = 0.95 ± 0.05, η = 0.75 ± 0.05 has been found for the spin-glass susceptibility χSG(L,T) and Binder parameter g(L,T).  相似文献   

7.
The low field Faraday rotation effect has been used to the investigation of the dynamic magnetic properties of the spin-glass Cd1-xMnxTe. The temperature and time dependence of the Faraday angle was investigated at T<Tc. It was shown that the thermal and magnetic history of the sample above Tc has the essential influence on the behavior below the critical temperature.  相似文献   

8.
The system La3-x( )xS4 [where ( ) denotes a vacancy] containing up to 25 at.% Gd is shown to be a model system in which magnetic interactions in metals can be studied. By measuring the temperature dependence of the low field a.c. susceptibility, the superconducting, spin-glass and ferromagnetic transitions can be determined as a function of the Gd concentration. The depression of the superconducting transition temperature mainly follows the theory of Abrikosov and Gor'kov, with a possibility for coexistence of superconductivity and spin-glass magnetic order near a critical concentration of 3 at.% Gd. The transition from spin-glass to ferromagnet is well-defined with the percolation limit for the long range ferromagnetic order at 14 at.% Gd.  相似文献   

9.
Prussian blue analogue FeII1.1CrIIx[CrIII(CN)6]0.6−x·nH2O nanowires were synthesized by electrodeposition. The magnetic properties investigation indicates that the nanowires exhibit cluster spin-glass behavior, which undergoes a magnetic transition to a frozen state below about 62 K. Spin disorder arising from reduced coordination and broken exchange bonds between spin centers due to the structural defects may be the reason that causes the spin-glass freezing behavior. The negative magnetization observed at temperature lower than the compensation temperature (Tcomp∼43 K) at a field of 10 Oe may be due to the different temperature dependences of the ferromagnetic site Fe-Cr and antiferromagnetic site Cr-Cr.  相似文献   

10.
The thermal evolution of the competition between the ferro-and antiferromagnetic exchange interactions in (Fe0.65Ni0.35)1?x Mnx alloys, which display different magnetic properties, depending on composition and temperature, is investigated. The distribution functions of the magnetic hyperfine fields P(B hf) for 57Fe are determined by Mössbauer spectroscopy in the temperature range 5–300 K for the alloys with x=0, 0.024, 0.082, 0.136, 0.195, and 0.252. The temperature dependence of the integrated intensity I s (T) is analyzed for the low-and high-field portions of P(B hf). The features found in the behavior of I s (T) are interpreted as results of variation of the ratio between the competing exchange interactions of different signs as a result of the thermal destruction of antiferromagnetic Fe-Fe exchange bonds. It is shown that the changes in the spin structure in the low-temperature range are due to the thermal destruction of Fe-Fe exchange bonds. One of the consequences of this destruction is “reentrance” (an increase in the hyperfine field with increasing temperature for some of the Fe atoms). The relationship between the thermal destruction of Fe-Fe exchange bonds and the magnetic transitions of the Fe-Ni-Mn system to the spin-glass state is considered.  相似文献   

11.
An electron spin resonance experiment has been performed on the Cr-rich concentrations of the random mixture Rb2Mn(1-x)CrxCl4 of an insulating ferromagnet (Rb2CrCl4) and an insulating antiferromagnet (Rb2MnCl4). The resonance fields in x = 0.6, 0.7 and 0.8 samples begin to shift towards low field side at temperatures well above the Curie temperatures, when the external field is applied in the c-plane of the crystal. The shift of the resonance field with temperature of the x = 0.7 sample agreed well with that of the x = 0.8 sample, after scaling the temperature axis, while the shift in the x = 0.6 crystal did not. From this observation, we argue that the x = 0.7 and x = 0.8 samples have a long-range ordered ferromagnetic phase below Tc, and that the low temperature phase of the x = 0.6 sample is not a truely long-range ordered one. A weak resonance line was observed in the x = 0.8 sample below about 20 K. This resonance is discussed in connection with the re-entrant spin-glass behavior of this mixed system found in the ac susceptibility measurement.  相似文献   

12.
A Mössbauer time window has been positively used for studying the behavior of spins in Fe x Mn1?x TiO3 withx=0.50, 0.60 and 0.65 which are of typical Ising spin-glass systems. Spin dynamics aboveT SG andT N (RSG) (definition is given in the text) are discussed. In the RSG samples, the existence of contributions of the transverse spin component to the hyperfine fields is pointed out.  相似文献   

13.
杨育清 《物理学报》1984,33(10):1454-1458
用超导量子干涉器(SQUID)磁强计对稀释磁性半导体Zn1-xMnxSe(0.1≤x≤0.50)的低温低场直流磁化率作了测量,测量温度从4.2K到30K,测量磁场为15Oe。当x≥0.30时,从磁化率-温度曲线的浑圆峰值,观察到了自旋玻璃的转变。自旋玻璃的转变温度Tf,对x=0.30,0.40,0.50,分别为10.5K,16K,19.5K。给出了顺磁相和自旋玻璃相的相图。比较了Zn1-xMnxSe和Cd1-xMnxSe的自旋玻璃转变温度,发现对同样的Mn离子浓度,Zn1-xMnxSe的Tf高于Cd1-xMnxSe的Tf,用交换作用的理论作了讨论。 关键词:  相似文献   

14.
In connection with the problem of identifying magnetic states in the vicinity of x 0 (the multicritical point of the x-T diagrams of spin-glass systems) a study has been made of properties that can be exploited to determine the presence of a thermodynamic phase transition at the Curie point T C and the distinctive features of the transition, specifically, the temperature dependence of the magnetic part of the specific heat C m(T), the temperature dependence of the low-field magnetization σ H(T), and (with a view toward examining critical behavior in a magnetic field) the magnetization isotherms σ H(T). The investigated object is the system of dilute ferrimagnetic spinels Li0.5Fe2.5−x GaxO4, in which every type of magnetic state has spatially inhomogeneous cluster structures. The results obtained for a sample with x=1.45 indicate that the classical criteria of a ferrimagnetic second-order phase transition at T C=(97±2) K occur for xx 0. The results of similar investigations for a sample with x=1.6, which exists in the cluster spin-glass state for T<T f=22 K and in an uncorrelated cluster state of the superparamagnetic type for T>T f, are also given for comparison with the preceding case. Zh. éksp. Teor. Fiz. 114, 2065–2077 (December 1998)  相似文献   

15.
It is demonstrated that 50% substitution of vanadium for molybdenum in the pyrochlore lattice of the complex oxide Y2(V x Mo1 ? x )2O7 results in a transition from the spin-glass ground state (at x = 0) to the ferromagnetic state in Y2VMoO7 (a = 10.1645(2) Å, T C = 55 K). The Gd2V0.67Mo1.33O7 compound (a = 10.2862(3) Å) is a ferromagnet with T C (84 K) exceeding that of undoped Gd2MnO2O7.  相似文献   

16.
Measurements of the critical temperature, Tc(x), the critical field, Hc2(x,T) and the susceptibility, χ (T), as a function de la concentration, x, in the system La3−x CexIn, are compared with the theories of Muller-Hartmann and Zittsrtz, and Abrikosov and Gor'kov. The Hc2(x, T = 0) and χ(T) measurements indicate the appearance of short range antiferromagnetic order around x = 0.04 which is probably responsible for the anomalous behavior of Tc(x).  相似文献   

17.
The magnetic properties of four compounds in the series CaBaCo4−xyZnxAlyO7 (x=0,1,2, y=0,1) were investigated. Using AC-susceptibility and DC-magnetometry, magnetic transitions (Tfs) were found for all four compositions in the range 50-3 K. The data from the AC measurements proved to be frequency dependent: Tf increases with higher frequencies. An energy-loss in the magnetic coupling, indicated as contributions in the imaginary part of the magnetic susceptibility (χ″), was seen for every compound and its maximum appeared just below the maximum χ′. Modelling the data with Arrhenius-, Vogel-Fulcher-, and the power-law made it possible to relate the four compounds to spin-glass materials. The Casimir-du Pré relation was used to extract average relaxation times at Tf. The DC magnetisations clearly show differences between field-cooled and zero-field-cooled measurements. None of the compounds exhibit any metamagnetic properties up to 8 T. A new method is presented to calculate the saturation fields using DC data. Relaxation measurements on three compounds indicate that the systems relax very fast, in contrast to spin-glasses. Aging does not affect the fast relaxations. The compounds are interpreted as disordered anti-ferromagnets with spin-glass features.  相似文献   

18.
Magnetic susceptibility χ measurements in the range from 2 to 300 K were carried out on samples of the Cu2FeSnSe4 and Cu2MnSnSe4 compounds. It was found that Cu2FeSnSe4 was antiferromagnetic showing ideal Curie-Weiss behavior with a Néel temperature TN of about 19 K and Curie-Weiss temperature θ=−200 K, while for Cu2MnSnSe4 the behavior was spin-glass with a freezing temperature Tf of about 22 K and Curie-Weiss temperature θ=−25 K. The spin-glass order parameter q(T), determined from the susceptibility data, was found to be in agreement with the prediction of conventional spin-glass theory.  相似文献   

19.
Results of the accurate magnetization measurements performed on the amorphous Fe10Ni70P14B6 alloy in the temperature range 20–77 K in fields upto 1 kOe are reported. The complex magnetic behaviour exhibited by this alloy has been analyzed to show that a ferromagnetic ordering, occuring on a localized microscopic scale at a temperature T0 very close to that given by the earlier Hall effect measurements, is accompanied by a superparamagnetic behaviour which below T0 causes at first a spin-glass freezing of the magnetic spins when they interact with one another on a long range scale and then a mictomagnetic freezing of the giant superparamagnetic clusters at a lower temperature as a result of exchange interaction between their moments and the frozen spin-glass matrix. In addition, the present results, besides providing a clear physical insight into the widely different ordering temperatures obtained for this alloy from previous Mössbauer and resistivity measurements, on one hand and from our magnetization measurements on the other, strongly suggest a magnetic origin for the observed resistivity-minimum phenomenon. In conclusion, the present alloy represents a composition in the amorphous (FexNi1?x)80P14B6 system well below the percolation limit.  相似文献   

20.
New magnetic system ZnxCa1−xFe2O4 (x = 0.4 to 0.6) is reported having extremely unusual properties like small ordered moments ≈ 0.13 ∼ 0.23 μB, large ordering temperatures Tc ≈ 700–750 K and surprising lack of hyperfine field (HF) at Fe for temperatures greater than T1(≈ 0.25 Tc) in spite of bulk magnetization in the system. The HF appears below T1 implying evolution of local moments far below Tc. Sharp susceptibility maxima resembling those of spin-glasses are observed for x = 0.4 and 0.5, which may be attributed to the single domain-superparamagnetic (SD-SP) transition and the overall behaviour shows a cluster spin-glass type of ordering.  相似文献   

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