Cluster Spin-glass Behavior Research Articles

Vacancy-induced spin-glass behavior of Prussian blue analogue Fe II1.1Cr IIx[Cr III (CN) 6] 0.6− x· nH 2O nanowires

Prussian blue analogue Fe II 1.1Cr II x [Cr III(CN) 6] 0.6− x · nH 2O 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 ( T comp ∼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.

Enhanced room temperature magnetoresistance and cluster spin glass behavior in Mo doping La0.67Sr0.33MnO3

The structural, magnetic, and transport properties of Mo doping La0.67Sr0.33Mn1−xMoxO3 (x=0–0.04) manganite system have been investigated by x-ray diffraction, scanning electron microscopy, magnetization, and magnetoresistance measurements. The Mo doping in Mn site is found to lower the Curie temperature Tc slightly and induce the cluster spin glass behavior in ferromagnetic state of La0.67Sr0.33MnO3. The room temperature magnetoresistance of Mo doping La0.67Sr0.33Mn1−xMoxO3 is found to be 50% higher than that of La0.67Sr0.33MnO3 without Mo doping. The significant enhancement for room temperature magnetoresistance could likely be attributed to the presence of the cluster spin glass state caused by the Mo doping.

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.

Disorder-induced short-range ferromagnetism and cluster spin-glass state in sol-gel derivedLa0.7Ca0.3Mn1−xCdxO3(0⩽x⩽0.2)

Low temperature magnetic and transport properties of the sol-gel derived Cd doped ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}{\mathrm{O}}_{3}(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.20)$ manganite system show ferromagnetism and cluster spin-glass behavior. Metal-insulator transition (MIT) is exhibited only by the samples with $x\ensuremath{\leqslant}0.1$; and for higher concentrations ($x=0.15$ and 0.20), samples are semiconductors. The MIT shifts to the lower temperature regime with increasing Cd content, indicating an increase of disorder in the system. Structural analysis shows local strain-induced small lattice distortion of the $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedra with Cd doping. With increasing Cd content, the system undergoes interesting paramagnetic to ferromagnetic (with $xl0.10$) as well as paramagnetic to cluster spin-glass (for $x\ensuremath{\geqslant}0.10$) transitions. ac susceptibility $({\ensuremath{\chi}}_{\mathrm{ac}})$ and magnetic relaxation measurements confirm this cluster spin-glass behavior. ${\ensuremath{\chi}}_{\mathrm{ac}}$ is found to follow the critical slowing down law $(\ensuremath{\tau}∕{\ensuremath{\tau}}_{0}={\ensuremath{\epsilon}}^{\ensuremath{-}z\ensuremath{\nu}})$. The magnetic hysteresis loops indicate a field-induced irreversible ferromagnetic phase due to the presence of ``weak'' antiferromagnetic domains in the samples with $x\ensuremath{\geqslant}0.10$. This typical behavior is found to be most prominent in the sample with $x=0.15$. The observed cluster spin-glass state is explained by considering the interactions between the ferromagnetic and antiferromagnetic clusters in these doped systems having disorder and reduced geometrical tolerance factor $t$, which resulted from the random substitution of Mn with Cd ions.

Large magnetoresistance in low temperature metallic region of manganite compounds (La 0.7−2 xEu x)(Ca 0.3Sr x)MnO 3 (0.05≤ x≤0.15)

Magnetoresistance (MR) and magnetization (dc and ac) measurements have been carried out on the manganites, (La 0.7−2 x Eu x )(Ca 0.3Sr x )MnO 3 (0.05≤ x≤0.15), in the temperature range of 5–320 K. At 5 K, an unusually large MR of almost 98% is observed in the x=0.15 sample, nearly up to fields of 4–5 T. This large high-field MR occurs in the metallic region, far below the insulator–metal transition temperature, and does not vary linearly with applied field. The unusual magnetoresistance is explained in the light of various possibilities such as phase segregation, cluster spin–glass behavior, etc.

Ferromagnetism in Fe-doped β-Ga2O3 Prepared by a Solid State Reaction

ABSTRACTPolycrystalline β-Ga2O3 doped with Fe3+, (Ga1−x Fex)2O3 (x=0.02, 0.05, 0.08 and 0.1), has been prepared by a solid-state reaction. Ferromagnetic ordering is observed at room temperature for samples prepared by β-Ga2O3 and Fe(NO3)3·9H2O and sintered at low temperatures below 900 °C, while the sintering at temperatures above 900 °C leads to the paramagnetic behavior. X-ray diffraction analysis for the samples sintered at 500 °C reveals that the single phase of β-Ga2O3 can be obtained up to x=0.08 without traces of secondary phase or other impurity. Magnetization as a function of temperature shows superparamagnetic or cluster spin-glass behavior, indicating that long-range ferromagnetic ordering does not exist in the present systems. It is suggested that the inhomogeneous distribution of Fe3+ is responsible for the ferromagnetic behavior.

Influence of Gd Doping at A Site upon the Magnetic Structureof La0.7-xGdxSr0.3MnO3 Systems

We investigated the magnetism of systemsLa0.7-xGdxSr0.3MnO3 (x = 0.00, 0.10,0.15, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70) by M-T curves, M-H curves,and electron-spin-resonance (ESR) spectra. The experimental resultsindicate that the system is in a ferromagnetic long-range order atlow-doping level; the samples of x = 0.30 and 0.40 show cluster-spinglass behaviour; and the antiferromagnetic characters are observed atx⩾0.50. For the samples of x = 0.30 and 0.40, the ESR spectrademonstrate that the phase separation occurs above the Curie temperature.

Unusual nanogranular systems

Melt-spun Co66Nb9Cu1Si12B12 metallic glass ribbon (TC≈150K) was used to produce a series of nanocrystalline samples differing in the volume content of the crystalline phase as well as the sizes of the crystallites. An analysis of the zero-field-cooled (ZFC) and field-cooled (ZF) dependences of magnetization showed that at low temperatures the samples displayed mictomagnetic (cluster spin-glass) behavior, whereas on increasing temperature a majority of the existing crystallites, beginning from those of the smaller sizes, gradually became superparamagnetic. These characteristics also showed that the existing dipolar interactions between the crystallites decreased the energy barrier for thermal relaxation. This effect was also well visible in the dependences of the temperature derivative of the difference of ZFC and FC magnetizations which reflected a distribution of the blocking temperatures of the crystallites.

Evolution of magnetic state in the La 1− xCa xMnO 3− γ ( x=0.30, 0.50) manganites depending on the oxygen content

The crystal structure, magnetic and electrical properties of the La 1− x Ca x MnO 3− γ ( x=0.30, 0.50; 0⩽ γ⩽0.50) oxygen-deficient manganites have been studied. It is found that the compounds La 0.70Ca 0.30MnO 3− γ possess a long-range ferromagnetic order up to γ=0.06 and a cluster spin glass behavior at 0.06< γ⩽0.20. Antiferromagnetic state of La 0.50Ca 0.50MnO 3− γ ( γ=0) composition transforms into inhomogeneous ferromagnetic one at γ=0.04. The system converts into cluster spin glass state at γ=0.10. As oxygen deficit reaches the value γ=0.25, a new type of ferromagnetic phase appears. The fraction of this ferromagnetic phase is the highest in the composition γ=0.30. It is supposed that the compounds with γ⩾0.35 represent an antiferromagnetic medium with inclusions of the ferromagnetic phase. The strongly reduced samples exhibit a large magnetoresistance below the temperature, at which the spontaneous magnetization develops. The magnetic phase diagrams of both La 0.70Ca 0.30MnO 3− γ and La 0.50Ca 0.50MnO 3− γ systems have been constructed. We argue, that the oxygen vacancies are disordered in the La 0.70Ca 0.30MnO 3− γ system in the studied region of oxygen vacancies concentration (0⩽ γ<0.20) whereas for the La 0.50Ca 0.50MnO 3− γ they tend to order at γ>0.25 in a manner of Sr 2Fe 2O 5-type crystal structure. This study shows that Mn 3+–O–Mn 3+ ferromagnetic interaction may play an important role in the formation of magnetic state of manganites.

Magnetic study on Co 0.2Zn 0.8Fe 2− xGa xO 4( x=0–1) spinel oxide

We report the magnetic study on a series of Ga substituted Co 0.2Zn 0.8Fe 2− x Ga x O 4 spinel oxide. The cations distribution, obtained from Mössbauer spectra, suggest that conventional ferrimagnetic structure, i.e., the existence of magnetic moments on both A and B sites, is destroyed for x⩾0.2 samples. We observe a non-monotonically increase of ferromagnetic correlations between the B site spins. The samples with x=0.2–0.6 shows a mixture of perturbed ferromagnetism and cluster spin glass behaviour. The perturbed ferromagnetic phase of the samples has been explained in terms of B site spin canting. The increase in magnetic frustration and competition between exchange interactions stabilizes the x⩾0.8 samples in a cluster spin glass like state. The field cooled thermoremanent magnetization measurement for x=0.4 sample suggest that the cluster nucleation process is not only thermally activated but also strongly depends on the temperature ( T a), where field has been applied during cooling process of the sample.

Magnetism of Ti4+ diluted manganites La1−xPbxMn1−yTiyO3 (y⩽x)

The effect of nonmagnetic Ti4+ substitution for Mn4+ on magnetic ordering of La1−xPbxMn1−yTiyO3 (x=0.15,0.26, and 0.4; 0⩽y⩽x ) has been studied. The ferromagnetic transition temperature and the magnetization decrease with increasing amount of titanium. Complete substitution of Mn4+ by Ti4+, for x=y, excludes the Mn3+–O–Mn4+ double exchange. However, these compounds still show ferromagnetism if the dilution of the Mn sublattice by Ti is small enough (y⩽0.2). This ferromagnetism probably originates from a ferromagnetic Mn3+–O–Mn3+ superexchange. A thorough study of magnetic properties including AC magnetic susceptibility, magnetization, temperature dependence of coercivity and relaxation of remanent magnetization has been carried out and gives evidence of cluster spin glass behaviour for La0.6Pb0.4Mn0.6Ti0.4O3.

Electrical transport, magnetism, and magnetoresistance in La 0.7 Sr 0.3 (Mn 1-x Co x )O 3

The crystal structure (rhombohedral) is not changed on the replacement of Mn by Co. The lattice parameters a and c decrease with the increasing Co concentration. In this paper we have systematically investigated the effect of Co doping on the Mn site in the La0.7Sr0.3MnO3 and find that Co substitution leads to a drastic suppression of ferromagnetic long-range order and metallic state. However, we observed substantial enhancement of MR ratio over the entire temperature studied for x=0.1 and a large increase of one at the low temperature for the compositions of x=0.2 and 0.3. The largest MR ratio as high as ≈78% is observed at 15 K in x=0.2 and 0.3. As x is further increased toward 1, conduction and ferromagnetism strongly recover but the MR ratio decreases obviously. The end member with x=1.0 has metallic and cluster spin-glass ferromagnetic behavior (T<TC) and a smaller value of MR (≈2–8%) in T<300 K with a maximum MR ratio of 8% at around TC (=238 K).

Low-lying magnetic excitations in amorphous and alloys

Results of high-resolution magnetization (M) measurements performed on amorphous (a-) (x = 0, 1, 2, 4, 6, 8, 10) and (y = 0, 1) alloys over wide ranges of temperature (T) and external magnetic field are presented and discussed in the light of existing theoretical models. The magnetization at 5 K does not saturate even for fields as high as 70 kOe particularly for the alloys with and y =0, 1. The high-field differential susceptibility at , is extremely large for the alloys with x = 0, 1 and y = 0, 1, and decreases rapidly with x for such that it possesses values typical of crystalline ferromagnets such as Fe, Co, Ni for x > 6. The dominant contribution to the thermal demagnetization of the spontaneous as well as `in-field' magnetization comes from spin-wave (SW) excitations at low temperatures and from enhanced local spin-density fluctuations over a wide range of intermediate temperatures and for temperatures close to the Curie point, , for all of the alloys studied. The spin-wave stiffness, D, is independent of for all of the compositions and the ratio possesses a value characteristic of amorphous ferromagnets with competing interactions for the alloys with and y = 0, 1. For these alloys, thermomagnetic and thermoremanent effects generally associated with the cluster spin-glass behaviour have been observed in the re-entrant state which sets in at a temperature . In accordance with the predictions of the spin-fluctuation model, D renormalizes with temperature as and the spin fluctuations get strongly suppressed by Co substitution and . While the spin-fluctuation (SF) model provides a consistent theoretical basis for the observed temperature dependence of the spontaneous and `in-field' magnetization over the entire temperature range , the infinite three-dimensional (FM) matrix plus finite FM spin-clusters model extends the scope of the SF model in that it offers a straightforward explanation for the absence of SW peaks in the inelastic neutron scattering spectra taken over a certain wave-vector-transfer range, the softening of spin-wave modes for , the existence of a significant contribution due to diffusons, in addition to magnons, to the -decrease of the magnetization, and the composition dependence of D(0), M(0,0) and .

Magnetic Phase Diagram of (Ni1−xMgx)O Solid Solutions

AbstractA magnetic phase diagram of the (Ni1−xMgx)O solid solutions is drawn by the results of elastic magnetic neutron scattering and magnetic measurements. The ranges of homogeneous antiferromagnetism (0 ≦ x ≦0.37), tricritical behaviour or frustrated antiferromagnetism (0.37 &lt; x ≦ 0.6), cluster spin glass (0.6 &lt; x ≦ 0.75) and paramagnetic behaviour of the Ni2+ spin moments in the ground state (x ≧ 0.8) are determined. It is shown that diamagnetic Mg2+ ions serve as a source of a random field inducing an extra diamagnetic moment of value 0.35μB.

Investigation of spin glass properties of AlCo alloys

Low field static magnetization and susceptibility measurements have been made in Co rich AlCo alloys. The experiments were carried out in the temperature range 4.2–80 K by using magnetic fields well below 100 mT. The results reveal cluster spin glass behavior with the associated history and time dependent effects for Co concentrations exceeding 51 at %. Below this concentration the temperature dependence of the susceptibility follows the Curie-Weiss law in the considered range of temperatures.

Magnetization and Mössbauer studies in RuSiFe x

Magnetization and 57Fe Mössbauer studies on a new series RuSiFe x (0.47⩽ x⩽2.0) are reported. T m is independent of x for x > 0.6. For x⪆1.3, the alloys are normal ferromagnets. However, HF(Fe) anomaly, akin to RuFeSi ( T hf⪡ T m), is observed for 1.2⪆x⪆0.6. For x<0.6, cluster spin glass behaviour is seen.