Reentrant Spin Glass Behavior Research Articles

Reentrant spin-glass behavior in phase-separated manganites

A typical reentrant spin-glass (RSG) behavior was observed and discussed for the phase-separated (Sm,Nd)0.5Ca0.5MnO3 manganites. The characteristic time constants of the spin-glass state were calculated based on the critical slowing down model. It was found that the characteristic time constant of the phase-separated (Sm,Nd)0.5Ca0.5MnO3 manganites are larger than those of the conventional SG state. Such results indicate that most probably there exist complicated magnetic interplays in the ground state of the compounds.

Ferromagnetism and antiferromagnetism in Ni 2+ x+ yMn 1− xAl 1− y alloys

The magnetic behavior of Ni 2+ x Mn 1− x Al alloys around the stoichiometric 2:1:1 composition was investigated with several experimental techniques. The results of low-temperature magnetization measurements indicate that a competition mechanism between ferromagnetism and antiferromagnetism is expected in off-stoichiometric alloys. Although the Curie temperature is strongly dependent on the composition, the saturation magnetization has an unsystematic variation for deviations from the stoichiometric Ni 2MnAl alloy. A reentrant-spin–glass behavior is observed below 50 K.

Magnetic ordering in Co 78− xMn xB 10Si 12 amorphous alloys studied using X-ray magnetic circular dichroism

Using X-ray magnetic circular dichroism (XMCD), effective magnetic moments for Co and Mn in Co 78− x Mn x B 10Si 12 amorphous alloys were estimated in order to explain the different magnetic states found in the amorphous alloy depending on the Mn content. As the Mn content was increased, the Co–Mn amorphous alloy changed from a ferromagnet to a paramagnet and then to a mictomagnetic state ( x = 30 at%) at room temperature. When x > 25 at%, a reentrant spin glass behavior was also observed below 50 K. XMCD analysis showed that the magnetic moments for both Co and Mn were severely reduced by the structural disorder. It was also found that the Mn–Mn pair exchange interaction was ferromagnetic, regardless of the composition (up to 30 at%); hence, antiferromagnetic J CoMn exchange interaction is believed to be responsible for the reentrant spin glass behavior as well as the mictomagnetic state observed for the alloys with high Mn content.

Small-angle neutron-scattering studies of reentrant spin-glass behavior in Fe–Al alloys

Fe–Al alloys around the concentration of 30 at. % Al show very interesting magnetic properties. Alloys with this concentration present magnetic inhomogeneities and their evolution with temperature is also interesting because they show a reentrant spin-glass behavior at low temperatures. Small-angle neutron-scattering measurements were performed in Fe69.5Al30.5,Fe70Al30, and Fe70.5Al29.5 alloys in the temperature range of 4–300 K. Even though the change in Fe content is very small, the response variation is quite large. The results show that the samples have magnetic inhomogeneities that evolve with temperature. Only in the Fe-richest sample the random-field model can be applied.

Mössbauer studies of the re-entrant spin-glass behaviour of Fe–Al alloys

Fe–Al alloys around the concentration of 30 at. % Al present re-entrant spin-glass behaviour at low temperatures. This behaviour is not completely understood and Mossbauer spectroscopy, combined with other experimental techniques, is useful to describe and explain this behaviour. Results show that the Mossbauer spectra coincide with the magnetic behaviour showed in literature and they can be explained as a magnetic cluster system whose magnetic clusters are getting smaller when the temperature is decreasing. When the temperature is reaching to the spin-glass transition at 92 K the spins in the paramagnetic matrix are moving slower and below this transition the spins are completely frozen.

Reentering spin glass behavior and charge ordering in phase separation Nd0.5Ca0.5MnO3 system

Half-doped manganese oxides are very important on clarifying physical mechanism of strong correlation electron system and colossal magnetoresistance (CMR) effec t due to their rich physical content. The structure, electrical and magnetic tra nsport properties of Nd0.5Ca0.5MnO3 manganite w as systemically studied. The results show that Nd0.5Ca0.5 MnO3 compound displays the O′-orthorhombic structure and indicate th e existence of the typical Jahn-Teller distortion under 300 K. The transport pro perties show that the system undergoes paramagnetic insulator-ferromagnetic meta l transition under a magnetic field of 8 T and is accompanied by CMR effect. Mea nwhile, it is found that the temperature of antiferromagnetic transition and cha rge ordering is around 150 and 240K, respectively. There appears a typical reent rant spin glass behavior around 41K and the negative magnetization is also obser ved in the compound. All these phenomena indicate that there exist several comp lex magnetic interactions in the ground state of this half-doped Nd0.5Ca0.5MnO3 compound at low temperature. The present result s provide experimental data for strongly electronic correlated system of manga nites.

Charge order phase and reentrant spin-glass behavior in half doped Sm0.5Ca0.5MnO3 manganite

The structure, transport and magnetic properties of half doped Sm0.5Ca0.5MnO3 manganite has been systamatically studied. The results show that Sm0.5Ca0.5MnO3 compound has the O′orthorhombic structure and shows typical Jahn-Teller distortion. Throughout the temperature range used, the electric transport shows semiconducting behavior and there are no I-M transition and CMR effect. Meanwhile, it is found that the charge-order and antiferromagnetic transition temperatures of the system are around 270K and 200K, respectively, whereas at lower temperature there appears a typical spin-glass state around 41K with reentrant behavior. The negative magnetization is also observed in this compound. All these phenomena indicate that for the ground state of Sm0.5Ca0.5MnO3, there exists the competition mechanism of several complex magnetic interactions. Present study may provide abundant experimental information for understandig the mechanism of the strongly electron correlated system.

Re-entrant spin glass behavior in Mn-rich YMnO3

We use magnetism and specific heat measurements to investigate the hexagonal Mn-rich YMnO3. It is found that upon cooling from a high temperature, the compound first orders antiferromagnetically at TN∼72K and then undergoes a re-entrant spin glass (RSG) transition at TSG∼42K. This RSG behavior results from the competition between the ferromagnetic interaction and the antiferromagnetic interaction, which is related to the intrinsic geometric magnetic frustration in this system.

Magnetic transitions in Dy-microalloyed Fe-based bulk metallic glasses

The magnetic properties of Fe70−xDyxZr8Mo5W2B15 (0 ⩽ x ⩽ 5) bulk metallic glasses (BMGs) are studied using dc and ac susceptibility measurements. A re-entrant spin glass behaviour is observed in the BMGs and the phenomenon is ascribed to Dy-microalloying-induced site frustration. The magnetic properties of the BMGs are found to be tunable by appropriate selection of the Dy content, and the schematic magnetic phase diagram as a function of Dy content is derived.

Reentrant Spin Glass Behaviour and CE-Type AntiferromagneticPhase in Half Doping (La,Pr)1/2Ca1/2 MnO3 Manganites

The reentrant spin glass behaviour was observed in half doping(La,Pr)1/2Ca1/2MnO3 manganites with a CE-typeantiferromagnetic structure. It shows sequential multiple magnetictransitions from the paramagnetic to the ferromagnetic,antiferromagnetic, spin glass (SG) transitions, which reflects thecomplex magnetic interaction in the ground state of manganites. Thiscan be explained by the competition interaction between theferromagnetic and the CE-type antiferromagnetic matrix, and thedisorder due to the tolerance factor t and A-cation size varianceσ2. The results reveals the coexistence of ferromagneticclusters and SG clusters in the background of the antiferromagneticmatrix in the ground state of half doping(Pr,La)1/2Ca1/2MnO3 systems.

Spin-glass behavior inLa(Fe1−xMnx)11.4Si1.6compounds

The magnetic properties of $\mathrm{La}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{)}_{11.4}{\mathrm{Si}}_{1.6}$ $(0<~x<~0.08)$ compounds were investigated. A reentrant spin glass behavior for the sample with $x=0.06$ and a paramagnetic-to-spin glass transition for the sample with $x=0.08$ were observed. The spin-glass behavior for the sample with $x=0.08$ was systematically studied by the dc and ac measurements. $\ensuremath{\Delta}{T}_{f}(\ensuremath{\omega})/[{T}_{f}(\ensuremath{\omega})\ensuremath{\Delta}{\mathrm{log}}_{10}\ensuremath{\omega}],$ a possible distinguishing criterion to assert the presence of a spin-glass phase was 0.02 for the sample with $x=0.08.$ The frequency-dependent data turned out to be well described by the conventional critical slowing down law $\ensuremath{\tau}/{\ensuremath{\tau}}_{0}={\ensuremath{\varepsilon}}^{\ensuremath{-}\mathrm{zv}}.$ The fit to this critical slowing down law yielded the values ${\ensuremath{\tau}}_{0}{=10}^{\ensuremath{-}12}\mathrm{s},$ $zv=8.28,$ and the transition temperature ${T}_{\mathrm{SG}}=45.24\mathrm{K}.$ This spin-glass behavior in $\mathrm{La}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{)}_{11.4}{\mathrm{Si}}_{1.6}$ compounds is mainly ascribed to the competing interaction between the Fe-Fe ferromagnetic ordering and the Fe-Mn, Mn-Mn antiferromagnetic ordering.

Reentrant spin-glass behavior in Fe–Zr–B amorphous alloys

Fe 91Zr 9 and Fe–Zr–B (Fe-rich >80%) amorphous alloys show a reentrant spin-glass behavior at low-temperatures that has been characterized by AC susceptibility measurements. Frequencies between 10 Hz and 10 kHz have been used to define the dynamic behavior. The reentrant spin-glass temperature T RSG is below 40 K for all cases, while Curie temperatures, T c range between 200 and 350 K. For the Fe 91Zr 9 the T RSG shift as a function of frequency is large compared to canonical spin-glass. The dynamic scaling shows a reentrant transition in Fe 91Zr 9 with a critical exponent zν=8.2. The effect of boron additions is to increase the T RSG frequency shift. This value becomes close to the values expected for superparamagnetic fine-particle systems. The relaxation kinetics are explained by means of a Vogel–Fulcher equation. The observed behavior should arise from a very inhomogeneous spin structure, in the form of magnetic clusters either of different composition or just of different density, which result in different exchange coupling values. The inclusion of boron atoms, even in reduced quantities, clearly affects the magnetic spin structure.

A new ferromagnetic thiospinel CuCrZrS4 with re-entrant spin-glass behaviour

A new thiospinel CuCrZrS4 has been successfully synthesized by a solid-state chemical reaction. This CuCrZrS4 exhibits ferromagnetic properties below the Curie temperature at T c = 60 -2 K. The appearance of irreversible effect between field-cooled and zero-field-cooled magnetization is prominent below around 5 K in a magnetic field of less than 150 Oe. The ac susceptibility χAC shows a rapid decrease below about 10 K. This low magnetic-field behaviour indicates the existence of a re-entrant spin-glass phase below about 10 K. The dc magnetic susceptibility above 100 K shows Curie-Weiss behaviour with an effective magnetic moment of 3.61 μ B, which is a little less than the spin-only value of 3.87 μ B for the Cr3+ ion. The asymptotic Curie temperature θ P is approximately 65 K, which is a little higher than T c. The valence state is confirmed to be Cu+Cr3+Zr4+S4 2− on the basis of magnetic properties. The electrical resistivity ρ shows a semiconducting temperature dependence over the temperature range from 4.2 to 280 K with an activation energy of 6.84 210−3 eV in the higher temperature range from 50 to 283 K.

Magnetic and Structural Properties of Fe–Mn–Al Alloys Produced by Mechanical Alloying

The effects of concentration and preparation conditions on the magnetic and structural properties of samples of the Fe-Mn-Al system prepared by mechanical alloying were studied by Mossbauer spectroscopy, X-ray diffraction and susceptibility techniques. X-ray diffraction showed that samples with high Al content (40 at.%) and prepared with low milling times (lest than 12 hours) present the peaks of Mn, Fe-Al alloy and broad peaks which correspond to the ternary bcc alloy. For 12 hours the Mn peak disappears and for 24 h or more the bcc ternary phase is totally formed. For t≥24 h Mossbauer spectroscopy studies proved that: samples rich in Fe are ferromagnetic (F) at room temperature (RT) and present a reentrant spin-glass (RSG) behavior for low T; samples with intermediate Fe values are paramagnetic (P) at RT and SG for low T; and those with low Fe content are P at RT, antiferromagnetic (AF) at low T and RSG at very low T. By ac magnetic susceptibility it was possible to detect an additional magnetic phase in the F and P regions which was attributed to a superparamagnetic (SP)-like behavior. XRD and Mossbauer spectroscopy of samples with low Al content (7.5 at.%) showed that they present a fcc AF phase and a Fe-Al F phase for low milling times (≤10 h). For bigger times the only detected phase is the fcc, which is AF for low Fe contents and P for high Fe contents. The effect of using small balls is to enhance the alloyed process.

Bulk Magnetic Properties of the Fe0.5Mn0.1Al0.4Disordered Alloy: A Monte Carlo Study

In this work we present a simulational study of the bulk magnetic properties of the Fe0.5Mn0.1Al0.4 disordered system. The magnetization per site, specific heat and magnetic susceptibility were obtained using Monte Carlo simulation. Simulation results were performed in the framework of a random site-diluted 3D Ising model with nearest neighbor interactions, and using a single-spin-flip Metropolis dynamics for equilibration and energy minimization, from which canonical ensemble and configurational averages were computed. In the simulation, atoms were randomly distributed on a body-centered cubic lattice in order to simulate the disorder and crystalline structure as obtained in the arc-melted Fe0.5Mn0.1Al0.4 alloy treated at high temperatures for long periods of time and followed by fast quenching. Competitive Fe–Fe ferromagnetic and Fe–Mn and Mn–Mn antiferromagnetic interactions were taken into account, as well as the Al dilutor effect. We conclude that, accordingly with Mossbauer results, the Fe0.5Mn0.1Al0.4 system exhibits a reentrant spin-glass behavior below 30 K characterized by a sharp increase of the mean hyperfine field attributed to the magnetic ordering of the Mn sublattice at these temperatures. Additionally, a ferromagnetic to paramagnetic transition at around 300 K was also evidenced.

Reentrant spin glass behavior in Cr-doped perovskite manganite.

The magnetic and transport properties of the Cr-doped manganites La(0.46)Sr(0.54)Mn(1-y)Cr(y)O3 ( 0 < or = y < or = 0.08) with the A-type antiferromagnetic structure were investigated. Upon cooling, we find multiple magnetic phase transitions, i.e., paramagnetic, ferromagnetic (FM), antiferromagnetic (AFM), and spin glass in the y = 0.02 sample. The low temperature spin glass state is not a conventional spin glass with randomly oriented magnetic moments but has a reentrant character. The reentrant spin glass behavior accompanied by the anomalous multiple magnetic transitions might be due to the competing interactions between the FM phase and the A-type AFM matrix induced by the random Cr impurity.

Reentrant spin glass behavior in layered manganite La1.2Sr1.8Mn2O7 single crystals

We report a detailed study of ac/dc magnetization and longitudinal/transverse transport properties of La1.2Sr1.8Mn2O7 single crystals below Tc=118 K. We find that the resistivity minimum at 40 K is related to the reentrant spin glass phase at the same temperature, accompanied by additional anomalous Hall effects. The carrier concentration from the ordinary Hall effects remains constant during the transition and is close to the nominal doping level (0.4 holes/Mn). The spin glass behavior comes from the competition between ferromagnetic double exchange and antiferromagnetic superexchange interactions, which leads to phase separation, i.e., a mixture of ferromagnetic and antiferromagnetic clusters, representing the canted antiferromagnetic state.

Spin-glass behavior of Zr(Fe xCr 1− x) 2 compounds

The magnetic properties of C14 Laves-phase Zr(Fe x Cr 1− x ) 2 (0.7⩽ x⩽0.85) alloys have been investigated. Arrott plots showed evidence of ferromagnetic ordering for alloys with x>0.7 but not for x=0.7. Zero field cooling/field cooling magnetization and Mössbauer spectroscopy data indicated spin-glass-like freezing for the sample with x=0.7 and a reentrant spin-glass behavior for samples with x>0.7. Dynamical behavior of the spin-glass sample ( x=0.7) was studied by means of AC susceptibility. Two critical lines described by T f (H)−T(0) ∼H 2/δ were obtained with δ=4.4 and 2.5, respectively.

Magnetic phase diagrams of Nb xFe 100− x and Ta xFe 100− x amorphous alloy systems

The magnetic phase diagrams of Nb x Fe 100− x and Ta x Fe 100− x amorphous alloy systems have been investigated. The phase transition from the paramagnetic state to the spin-glass state was observed above about x=34% for Nb x Fe 100− x and x=36% for Ta x Fe 100− x amorphous alloys. The re-entrant spin-glass behavior was confirmed below these concentrations. The saturation magnetic moment M s of both amorphous alloy systems decreases with increasing x. The value of M s at the concentration where the spin-glass state takes place is small of about 0.4 μ B per Fe atom due to the short average Fe–Fe interatomic distance, compared with that of other Fe-based amorphous alloy systems such as La–Fe, Ce–Fe and Lu–Fe. The magnetic phase diagrams of the Nb–Fe and Ta–Fe amorphous alloy systems are similar to those of other Fe-based amorphous alloy systems, although the Curie temperature and the magnetic moment of the former two systems are much lower than those of the latter alloys systems.

Low-temperature magnetic phases of amorphous (Fe 1− xRE x) 0.7Zr 0.3 (RE=Ho, Dy)

Linear and nonlinear AC susceptibilities and DC magnetization measurements have been made on mechanically alloyed amorphous (Fe 1− x RE x ) 0.7Zr 0.3 ( x⩽0.4, RE=Ho, Dy). Various magnetic phases at lower temperatures appear as a function of x, exhibiting especially spin freezing behaviors due to the random magnetic anisotropy (RMA) of RE atoms, i.e., spin glass-like behavior for x∼0.1, ferrimagnetic-like behavior for x∼0.2, reentrant spin glass behavior for x∼0.3 and speromagnetic behavior for x∼0.4. Magnetic phase diagrams under the magnetic field and ordering characteristics are discussed by considering both the RMA and the random competing ferromagnetic Fe–Fe and antiferromagnetic Fe–RE interactions.