Spin Glass-like Behavior Research Articles

Magnetic disorder in nanostructured Fe7Au93 films and Fe14Au86 powders

Thin films and powders of dilute Fe-Au alloys have been produced by DC-magnetron sputtering and high-energy milling, respectively. Energy disperse X-ray spectroscopy gives Fe7Au93 for the films and Fe14Au86 for the powders. The film, with a thickness below 200 nm measured by atomic force microscopy, was deposited onto a Si(100) substrate. X-ray diffraction reveals a major presence of fcc-Au peaks masking the bcc-Fe phase. The (1 0-300 K) DC-susceptibility (H = 100-1000 Oe) shows a clear cusp in the films in contrast to the powders, with a reentrant spin glass-like behavior.

Role of dipolar interactions in a system of Ni nanoparticles studied by magnetic susceptibility measurements

The role of dipolar interactions among Ni nanoparticles (NPs) embedded in an amorphous ${\text{SiO}}_{2}/\text{C}$ matrix with different concentrations has been studied performing ac magnetic susceptibility ${\ensuremath{\chi}}_{\text{ac}}$ measurements. For very diluted samples, with Ni concentrations $<4\text{ }\text{wt}\text{ }%$ Ni or very weak dipolar interactions, the data are well described by the N\'eel-Arrhenius law. Increasing Ni concentration to values up to $12.8\text{ }\text{wt}\text{ }%$ Ni results in changes in the N\'eel-Arrhenius behavior, the dipolar interactions become important, and need to be considered to describe the magnetic response of the NPs system. We have found no evidence of a spin-glasslike behavior in our Ni NP systems even when dipolar interactions are clearly present.

Multiferroic behavior in silicate glass nanocomposite having a core–shell microstructure

Nanosized iron core and barium titanate shell microstructure was generated within a silicate glass of composition 23.1 Na 2O, 23.1 BaO, 23.0 TiO 2, 7.6 B 2O 3, 5.8 Fe 2O 3, 17.4 SiO 2 by first reducing it at 893 K for ½ h and then subjecting it to heat treatment at 759 K for 4 h. Transmission electron microscopy showed the composite particles to have a mean diameter of 3.9 nm. The nanocomposite exhibited both ferroelectric and ferromagnetic behavior. The dielectric constant peak was not prominent because of a small thickness of the barium titanate phase. The magnetic hysteresis loop showed an asymmetric behavior giving rise to a small exchange bias field. This is believed to arise due to exchange interaction between the ferromagnetic iron core and the thin layer of Fe 3O 4 on the core surface with a spin glass-like behavior. The magnetization under zero-field cooled (ZFC) and field cooled (FC) conditions indicated superparamagnetic behavior at temperatures higher than 300 K. The optical absorption spectra exhibited a peak at around 325 nm. This was analyzed satisfactorily on the basis of a metal core–oxide shell nanoconfiguration. The extracted values of metal core conductivity showed a metal insulator transition for iron core diameters less than 2.4 nm. The present synthesis approach will lead to newer multiferroic nanocomposites and glasses with multifunctionalities.

Spin-glasslike behavior in rhombohedral (Ge,Mn)Te–(Sn,Mn)Te mixed crystal

We present studies of magnetic and transport properties of Ge1−x−ySnxMnyTe mixed crystals with chemical compositions 0.083≤x≤0.142 and 0.012≤y≤0.119. The transport characterization measurements were performed at temperatures 4.2<T<300 K. The results showed feature characteristic for narrow gap semiconductors, e.g., metallic conductivity with ρxx≈10−4 Ω cm and hole concentrations p>1021 cm−3. It was found that the transport properties strongly depend on the chemical composition of the alloy. The magnetic investigations included measurements of linear χ1 and harmonic χ2,3 ac susceptibilities as a function of temperature and of the applied magnetic field amplitude and frequency. Qualitative analysis of our experimental data showed that in the studied system, in the investigated composition range, the spin glass order exists at temperatures up to 50 K.

Spin-glasslike behavior of K+-containing α-MnO2 nanotubes

Magnetic properties of K+-containing α-MnO2 nanotubes have been systematically investigated by dc magnetic measurements. Zero-field-cooled and field-cooled susceptibilities display divergences at low temperature, and a spin-glass temperature of 33.1 K is determined from the de Almedia–Thouless line by extrapolating the applied field to zero. The dc magnetic measurements, such as the field dependent magnetic susceptibility, hysteresis effect, thermoremanent magnetization, and memory effect, further confirm the spin-glass feature of the tetragonal α-MnO2 sample, which can be attributed to the geometrical frustration on the triangular lattices and the mixed valence of Mn3+ and Mn4+.

Magnetic phase transition of the bond random mixed compound Fe(Br x I1 − x )2

The single crystal samples of Fe(Br x I1 − x )2 were investigated by the magnetization measurement. Among them, the x = 0.6, 0.8 and 0.9 samples were microscopically studied by the Mossbauer technique. As comparing the results of a magnetic behavior obtained for the x = 0.6, 0.8 and 0.9 samples, we discuss a spin glass-like behavior appeared in the bond random mixture. We propose an x–T magnetic phase diagram of Fe(Br x I1 − x )2.

Magnetic behavior of Fe and Tm in Zn–Fe–Sc–Tm icosahedral quasicrystals

Abstract The magnetic properties of p-type Zn77Fe7Sc16–x Tm x (x = 0, 1, 2, 4 and 6) icosahedral quasicrystals have been investigated. The magnetic susceptibility of these samples obeys Curie-Weiss paramagnetism in 72–300 K. The estimated Curie constants indicated that 3d Fe magnetic moments also exist besides 4f Tm in these quasicrystals. In the lower temperature region, spin glass-like behavior was observed for all samples with freezing temperature 7.0–9.5 K. For samples with higher concentration of Tm, namely x = 2, 4 and 6, the magnetic susceptibility increase as temperature decrease below the freezing temperature. This behavior indicates weak antiferromagnetic interaction between 4f Tm magnetic moments.

Spin glass-like behaviour in Ce-based Kondo systems arising from d-type nonmagnetic atoms disorder

The effect of Rh or Sb doping in Kondo insulator CeNiSn, and Rh doping in the Kondo lattice system CePdAl is investigated. The studies indicated the spin glass-like states in these materials caused by a statistical distribution of the nonmagnetic transition elements.

Observation of magnetoelectric coupling in glassy epitaxial PbFe0.5Nb0.5O3 thin films

The temperature evolution of the dielectric spectra in PbFe0.5Nb0.5O3 (PFN) thin films showed a kink near the Néel temperature (∼170 K), diffuse phase transition (327–380 K) with frequency dispersion at dielectric maxima temperature, and almost frequency independent maxima at 600 K, suggesting weak magnetoelectric coupling, relaxor behavior, and structural phase transition, respectively. Dielectric properties and magnetic hysteresis revealed the coexistence of relaxor ferroelectricity and weak ferromagnetism at room temperature in PFN films. The magnetization as a function of temperature revealed a cusp in the zero field cooled curve for low magnetic field (∼100 Oe) near 170 K, suggesting spin glasslike behavior.

Anisotropic magnetization and dynamic susceptibility sign change in single-crystalNa0.85CoO2

The dc and ac magnetic susceptibilities of ${\text{Na}}_{0.85}{\text{CoO}}_{2}$ single crystals were measured for the different crystal orientations of $H\ensuremath{\parallel}(ab)$ and $H\ensuremath{\parallel}(c)$ axis. The dc-magnetic susceptibility for $H\ensuremath{\parallel}(c)$ direction exhibited the antiferromagnetic transition at ${T}_{N}=22\text{ }\text{K}$. The thermal hysteresis between the zero-field-cooled and the field-cooled magnetization below ${T}_{N}$ and the large frustration parameter indicated the spin frustration along the $c$ axis. For an applied magnetic field in $H\ensuremath{\parallel}(ab)$ plane, the dc magnetic susceptibility exhibited the logarithmic divergent behavior at low temperatures $(T\ensuremath{\le}6.8\text{ }\text{K})$. This could be understood by the impurity spin effect dressed by the spin fluctuation. From the ac magnetic susceptibility measurements, the real part of the ac susceptibility for $H\ensuremath{\parallel}(ab)$ exhibited the spin glasslike behavior at low temperatures $(T\ensuremath{\le}4\text{ }\text{K})$. Remarkably, for an applied ac magnetic field with $H\ensuremath{\parallel}(c)$ axis, the sign of the ac magnetic susceptibility changed from a positive to a negative value with increasing ac magnetic field frequency $(f\ensuremath{\ge}3\text{ }\text{kHz})$ at low temperatures $(T\ensuremath{\le}7\text{ }\text{K})$. We interpret the sign change of ac magnetic susceptibility along the $c$ axis in terms of a sudden sign reversal of the phase difference $\ensuremath{\phi}$ from in-phase to out-of-phase response with an applied ac magnetic field in the ac-susceptibility phase space.

Magnetism in Gd–W films

Vapor condensation techniques are useful to prepare magnetic alloys whose components have low or even negligible equilibrium mutual solubility. In this work, one of these techniques—sputtering—was used to obtain GdxW1−x alloys whose magnetic properties were investigated as a function of the Gd atomic concentration x. Gadolinium and various Gd-based alloys are promising materials for magnetic refrigeration and this was one of the motivations for this study. The Gdx–W1−x films were sputter deposited from Gd and W targets with x ranging from 0 to 1 as determined by x-ray energy-dispersive spectroscopic analyses. X-ray diffraction patterns indicate that crystalline structures were formed at low and high Gd concentrations, while at intermediate concentrations, the films were amorphous. Magnetization measurements, performed as a function of temperature and with static and alternating applied fields, reveal a spin glasslike behavior in all the W-containing samples for temperatures below the freezing temperature Tf. For low and intermediate Gd concentrations, and for T>Tf, the films were paramagnetic, while a ferromagnetic phase was observed in the Gd–W alloy of the highest Gd content. The magnetocaloric effect was investigated from the magnetization isotherms M versus H, from which the isothermal magnetic entropy variation ΔSM as a function of T, for the removal of an applied field of 50kOe, was determined. It was observed that the maximum value of ΔSM for each ΔSM versus T curve and the temperature at which these maxima occur, are strongly dependent on x.

Characteristics of MnxSi1-xTe Compound Studied by Electron Magnetic Resonance and Other Experiments

The magnetic and other physical characteristics of <TEX>$Mn_xSi_{1-x}Te$</TEX> have been investigated by electron magnetic resonance (EMR), X-ray diffraction (XRD) and other experiments. <TEX>$Mn_xSi_{1-x}Te$</TEX> is found to have corundum structure for manganese contents up to 10% and also to be ferromagnetic for temperatures below 80 K. While ferromagnetic resonance signal coexists with the usual paramagnetic resonance signal, invariance of the g-factor inferred from the electron paramagnetic resonance signals throughout all temperature ranges clearly confirms that the manganese ions are in the electronic 3d5 state. The temperature dependence of EMR line-width is the same as other diluted magnetic semiconductors. From the EMR signals relaxation times <TEX>$T_2$</TEX> and <TEX>$T_1$</TEX> of <TEX>$Mn_xSi_{1-x}Te$</TEX> compounds are estimated to be about <TEX>$4.4{\times}10^{-10}s$</TEX> and <TEX>$9.3{\times}10^{-8}s$</TEX> respectively and are found to vary slightly with temperature or composition change. Exchange narrowing of the EMR line-width becomes dominant for the sample in which the substitution ratio, x = 30%. For one sample, in which x = 0.5%, spin glass-like behavior is indicated by EMR signals for temperatures lower than 60 K. This behavior may authentic for samples within a certain range of x.

Structural and magnetic properties of polycrystalline La0.77Sr0.23Mn1−xCuxO3 (0≤x≤0.5) manganites

The effect of the substitution for Mn with Cu in the polycrystalline La0.77Sr0.23Mn1−xCuxO3 (0 ≤ x ≤ 0.5) manganites upon the structural and magnetic properties has been investigated by means of X-ray diffraction (XRD) and magnetization measurements. The results indicate that replacing Mn by Cu in La0.77Sr0.23Mn1−xCuxO3 system led to a change in crystal structure at room temperature from rhombohedral phase (R-3c space group) to orthorhombic phase (Pmna space group) at x ≥ 0.3. Paramagnetic to ferromagnetic phase transition at Curie temperature, TC, is observed. It was found that substitution of Cu on the Mn site causes a reduction in TC. The analysis of the crystallographic data suggested a strong correlation between structural and magnetism, for instance a relationship between a distortion of the MnO6 octahedron and the reduction in the Curie temperature. At x ≥ 0.3 the spin glass-like behaviour is evidence by a cup in the temperature-dependent magnetization, M(T), curves due to the appearance of antiferromagnetic (AFM) superexchange interaction imposed with ferromagnetic (FM) double exchange (DE) interaction. The variation of the effective magnetic moment, μeff, upon Cu-doping level at B-site is analyzed in terms of structure phase transition. Magnetization at lower temperatures is less in the doped samples and decreases with increasing the Cu contents. A reduction in the saturated magnetic moments with increasing of the Cu substitution is observed in the concentration range x = 0–0.2.

Cluster spin-glasslike behavior in nanoparticles of diluted magnetic semiconductors ZnS:Mn

Zn1−xMnxS nanoparticles with x = 0.08, 0.16, and 0.32 were synthesized by a coprecipitation reaction between nitrate and sodium sulfide at room temperature in air. The magnetic properties of the Zn1−xMnxS nanoparticles were investigated by alternating-current (ac) susceptibility and direct-current (dc) magnetization measurements. The Mn3O4 phase was observed to exist in the Zn1−xMnxS nanoparticles as x ⩾ 0.16. The actual concentrations (x) of Mn-doped ZnS nanoparticles were determined by energy-dispersive x-ray analysis (EDAX) to be 0.06, 0.11, and 0.20, respectively, corresponding to the initial concentrations x = 0.08, 0.16, and 0.32. All the nanoparticles had the cubic structure and the lattice constant of Zn1−xMnxS phase increased with increasing Mn dopant concentration. For the Zn0.68Mn0.32S nanoparticles, there was evidence for appearance of cluster spin-glasslike behavior, as indicated by two maxima around 15 and 25 K in temperature dependence of ac susceptibility. The frequency independence of the peak at higher temperature is related to the intracluster ferromagnetic (FM) interactions, and the frequency dependence of the peak at lower temperature is associated with the spin glass. All the results revealed that the concentration of Mn2+ in Mn–ZnS and the amount of Mn3O4 were crucial for the cluster spin-glass behavior, which was not found when the real concentration (x) was unequal to 0.20 in Zn1−xMnxS.

Magnetic properties of the Cu xIn yCr zSe 4 single crystals

Magnetic properties of the spinel single crystals with the general chemical formula Cu x In y Cr z Se 4 (where y = 0.074, 0.1, 0.12, 0.15, 0.16, 0.48, 0.54 and 1.14) have been studied. Ferromagnetic ordering with a Curie temperature of 330 K up to y = 0.16, spin glass-like behavior with freezing temperature of 36 K for y = 0.48 and the antiferromagnetic ordering with Néel temperature of 21 K for y = 0.54 were established. The results above mentioned are related to the exchange integrals, suggesting that with increasing indium ions with tetrahedral coordination a local competition of both superexchange ferromagnetic and antiferromagnetic interactions undergoes a complex order–disorder–order transition with the reversal spin.

Magnetic Behaviour and Heating Effect of Fe3O4Ferrofluids Composed of Monodisperse Nanoparticles

Fe3O4 ferrofluids containing monodisperse Fe3O4nanoparticles with different diameters of 8, 12, 16 and 18 nm areprepared by using high-temperature solution phase reaction. Theparticles have single crystal structures with narrow size distributions.At room temperature, the 8-nm ferrofluid shows superparamagneticbehaviour, whereas the others display hysteresis properties and thecoercivity increases with the increasing particle size. The spinglass-like behaviour and cusps near 190 K are observed on allferrofluids according to the temperature variation of field-cooled (FC)and zero-field-cooled (ZFC) magnetization measurements. The cusps arefound to be associated with the freezing point of the solvent. As acomparison, the ferrofluids are dried and the FC and ZFC magnetizationcurves of powdery samples are also investigated. It is found that theblocking temperatures for the powdery samples are higher than those fortheir corresponding ferrofluids. Moreover, the size dependent heatingeffect of the ferrofluids is also investigated in ac magnetic field witha frequency of 55 kHz and amplitude of 200 Oe.

Lanthanide–3d cyanometalate chains Ln(iii)–M(iii) (Ln = Pr, Nd, Sm, Eu, Gd, Tb; M = Fe) with the tridentate ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz): evidence of ferromagnetic interactions for the Sm(iii)–M(iii) compounds (M = Fe, Cr)

A series of cyanide-bridged chain mixed Fe(III)/Ln(III) (Ln=Pr, Nd, Sm, Eu, Gd, Tb) complexes with the tridentate ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz) used as a capping group has been prepared. Reactions of tptz and LnCl3 with K3Fe(CN)6 yield a family of air-stable 1-D compounds {[Pr(tptz)(H2O)4Fe(CN)6].8H2O}infinity, {[Nd(tptz)(H2O)4Fe(CN)6].8H2O}infinity, {[Sm(tptz)(H2O)4Fe(CN)6].8H2O}, {[Eu(tptz)(H2O)4Fe(CN)6].6H2O}infinity, {[Gd(tptz)(H2O)4Fe(CN)6].6H2O}infinity, and {[Tb(tptz)(H2O)4Fe(CN)6].8H2O}infinity. Temperature dependent magnetic susceptibility studies of reveal that in , the Sm(III) and Fe(III) ions are ferromagnetically coupled with 3-D ordering occurring below 3.5 K. The appearance of the frequency dependent out-of-phase signal is explained in terms of an ordering with a spin glass-like behavior. To compare the magnetic behavior of with related compounds, {[Sm(tptz)(H2O)4Co(CN)6].8H2O}infinity and {[La(tptz)(DMF)(H2O)3Fe(CN)6].5H2O}infinity, {[Sm(tmphen)(DMF)3(H2O)Fe(CN)6].2H2O}infinity, {[Sm(tmphen)2(H2O)2Fe(CN)6].MeOH.13H2O}infinity and {[Sm(tmphen)2(H2O)2Cr(CN)6].MeOH.9H2O}infinity with 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) were also prepared.

Glass-like and Verwey transitions in magnetite in details

We have measured low field DC and low frequency AC magnetic properties of single crystals of magnetite with continuously reading high-resolution SQUID magnetometer in temperature range from 5 to 150 K . The measurements show hysteresis of Verwey transition in temperature and linear opening of energy gap of about 40 meV above the transition. Below the transition an AC response may be well explained by a thermally activated charge hopping. For frequencies of the driving AC field close to the hopping frequency a spin glass-like behavior is observed. Extracted values of the energy gap, activation energy and attempt period agree with those found from infrared complex conductivity measurements. Characteristic temperature of the glass-like transition coincides with minimum of the spin–spin relaxation time observed by NMR with this sample. Both NMR and our data may be explained consistently on the basis of the fluctuation-dissipation theorem.

Spin glass-like behavior, giant magnetocaloric and giant magnetoresistance effect in PrPb manganites

The Pr 1− x Pb x MnO 3 ( x=0.1–0.5) perovskites have been fabricated by solid-state reaction. The X-ray diffraction patterns show that the samples are of single phase with orthorhombic structure. The field-cooled (FC) and zero-field-cooled (ZFC) thermomagnetic curves measured at low field and low temperatures exhibit the spin glass-like state. The Curie temperature of samples increased with increase in Pb content. The maximum magnetic entropy change |Δ S m| max reaches the giant values of 3.91 and 3.68 J/kg K for quite low magnetic field change of 1.35 T for the samples x=0.1 and 0.4, respectively. The resistance measurements show that there is insulator–metal phase transition on the R( T) curves for samples with x⩾0.3. The giant magnetoresistance effect is also observed for all samples studied.

Magnetic behavior of the bond random mixed compound FE(BR x I1−x )2(x = 0.9) with Mössbauer spectroscopy

The bond random mixed compound Fe(Br0.9I0.1)2 has been studied by magnetization and Mossbauer measurements. Although the zero-field cooled and fieldcooled magnetization variations are not like a typical spin glass one, the Mossbauer spectrum below Neel temperature shows a hyperfine field distribution. It implies that the 10% FeI2 mixed in FeBr2 can be induced by the bond random effect which causes the sample to exhibit a spin glass-like behavior.