Reentrant Spin Glass Behavior Research Articles

Mössbauer study of the re-entrant spin-glass behaviour in the mixed spinel ferrites Mg (0.9+x)Fe 2(1−x)Ni 0.1Ti xO 4 ( x=0.5 and 0.6)

Samples of the mixed spinel ferrite series Mg (0.9+ x )Fe 2(1− x )Ni 0.1Ti x O 4 with x=0.5 and 0.6, prepared by solid state reaction of the appropriate oxides, have been investigated with 57Fe Mössbauer spectroscopy. The as-prepared samples are found to be mainly superparamagnetic due to magnetic cluster formation. Samples after at least three times reheated exhibit spectra, which can be rather interpreted by a transversal relaxation of the spin above and spin-glass behaviour below the respective freezing temperatures T f . External-field spectra reveal the canting to occur only on the octahedral sites. From the derived transition temperatures and thresholds together with data from earlier investigated sample with x=0.7 a compositional magnetic phase diagram for this spinel series is obtained.

Observation of reentrant spin glass behavior inLaCo0.5Ni0.5O3

The magnetic and transport properties of LaCo0.5Ni0.5O3 have been studied. The dc magnetization and the ac susceptibility studies suggest the presence of a magnetic-phase transition from a ferromagnetic (FM) to a spin glass phase at a low temperature. This type of reentrant spin-glass (RSG) behavior attached to a long-range ordered ferromagnet is observed in this system. A magnetoresistance of ~10% is observed at 5 K which is unsaturated up to 11 Tesla suggests the presence of antiferromagnetic (AFM) interactions. It is likely that the competition between such AFM interactions with FM interactions yield an RSG phase.

Effect of annealing treatment on the magnetic properties of mechanochemical synthesized [formula omitted] manganites

In this paper, we have investigated the effect of annealing on structural and magnetic properties of La 0.8Pb 0.2MnO 3 (LPMO) polycrystalline samples. Mechanochemical procedure has been used to produce LPMO nanocrystalline samples from oxide precursors. From the AC susceptibility measurements we found that the magnitude of susceptibility increases and the paramagnetic–ferromagnetic (PM–FM) transition width decreases by annealing the ball milled powders. Also, reentrant spin glass (RSG) behavior has been found in high temperature annealed samples. It seems that, due to the evaporation of PbO in high temperature annealed samples, vacancies created in perovskite structure and portion of the Mn 3+–O–Mn 4+ network is broken. So the FM double-exchange interaction is weakened due to the magnetic dilution and the antiferromagnetc (AFM) phase fraction increases in high temperature annealed samples. The competition between FM double-exchange interaction and AFM super-exchange interaction produces spin frustration and is responsible for the occurrence of RSG.

Reentrant spin glass behavior in La 0.8Sr 0.2Mn 1− xTi xO 3 manganites

In this study, the effect of Ti substitution on structural, electrical and magnetic properties of La 0.8Sr 0.2Mn 1− x Ti x O 3 ( 0 ≤ x ≤ 0.075 ) are investigated by XRD, electrical resistivity and ac susceptibility measurements. The XRD refinement result indicates that the lattice parameters and volumes increase by an increase of the Ti doping level. The resistivity measurement results show that by increasing the Ti doping level, the metal insulator transition temperatures decrease and system becomes an insulator. The paramagnet–ferromagnet transition temperature, T c also decreases as the Ti content increases. The reentrant spin glass (RSG) state exists in the x = 0.05 and 0.075 samples. The RSG behavior is mainly ascribed to an increase of disorder in the FM matrix induced by the random Ti impurity substitution.

Ferromagnetic insulating and reentrant spin glass behavior in Mg doped La0.75Sr0.25MnO3 manganites

Abstract In this study, the effect of Mg substitution on structural, magnetic and electrical properties of La0.75Sr0.25Mn1−xMgxO3 and La0.75Sr0.25−xMgxMnO3 (nominal compositions) samples are investigated by XRD, Ac susceptibility and electrical resistivity measurements. It is found that Mg does not replace La in the perovskite lattice. Also the results show that by increasing Mg doping levels, the paramagnetic–ferromagnetic and metal–insulator transition temperatures decrease. The reason for decreasing transition temperatures with increasing Mg concentration is, that the long-range FM order has been destroyed by the Mg, which is randomly occupying Mn site. This leads to the suppression of double-exchange interaction in the Mn3+–O–Mn4+ networks. Also the reentrant spin glass (RSG) state accompanied by FM transition, exists in high doped samples. The RSG state could be understood on the basis of double exchange ferromagnetic interaction in Mn3+–O–Mn4+ and super-exchange antiferromagnetic interaction in the Mn4+–O–Mn4+ networks.

Study of thiospinel

Abstract We report the results of μ SR measurement of the re-entrant spin-glass thiospinel CuCrZrS 4 . We have observed a relatively small enhancement of the relaxation rate at T C ∼ 60 K but no oscillations in the time spectra in the first magnetic phase between T C and T f ∼ 7 K , suggesting that the first magnetic phase is not a long-range ordering state. A fast depolarization component in ZF- μ SR appears around 40 K and develops accompanied by the rapid increase of its relaxation rate with decreasing temperature down to T f . The fast depolarization component is interpreted as the signature of the magnetic correlation attributed to the re-entrant spin-glass behavior. At all the measured temperatures, there remain relaxations even at high magnetic fields, revealing a dynamical local field due to strong magnetic correlations.

Oxygen vacancy induced re-entrant spin glass behavior in multiferroic ErMnO3 thin films

Epitaxial thin films of hexagonal ErMnO3 fabricated on Pt(111)/Al2O3(0001) and yttria-stabilized zirconia(111) substrates exhibited both ferroelectric character and magnetic ordering at low temperatures. As the temperature was reduced, the ErMnO3 films first showed antiferromagnetism. At lower temperatures, the films deposited at lower oxygen partial pressures exhibited spin glass behavior. This re-entrant spin glass behavior was attributed to competition between an antiferromagnetic interaction in the hexagonal geometry and a ferromagnetic interaction caused by a change in Mn valence induced by excess electrons from the oxygen vacancies.

Investigation of the chemical homogeneity of Cu 80(Fe,Co) 20 powders produced by mechanical milling

Cu 80Fe 14Co 6 and Cu 80Fe 6Co 14 alloys were elaborated by high-energy ball milling of pure Cu, Fe and Co powders for times up to 20 h. X-ray diffraction, 57Fe Mössbauer spectrometry and ZFC/FC magnetic measurements show that milling the powders for times up to 6 h leads to the progressive dissolution of Fe and Co atoms into Cu, forming a so-called “solid solution”. For longer milling times, the structure of the as-milled powder does not change. However, the magnetic behaviour reveals that local chemical inhomogeneities exist. In some regions, the composition is similar to the nominal composition of the starting powder: Fe and Co atoms are dissolved in Cu and give rise either to a reentrant spin-glass behaviour in Cu 80Fe 14Co 6 powders, or to a spin-glass behaviour in Cu 80Fe 6Co 14 powders. Some other regions are enriched in Fe and Co and probably contain nanometer-sized α-Fe and α-Co precipitates that lead to a superparamagnetic behaviour at room temperature. The occurrence of such inhomogeneities have been confirmed by field ion microscopy observations and tomographic atom probe investigations, that clearly show that the Cu–Fe–Co solid solution which is formed after milling pure Cu, Fe and Co powders is chemically non-homogeneous.

Magnetic behavior and magnetocaloric effect of neodymium-based amorphous alloy

The Nd49Al13Ni38 amorphous alloy has been prepared by melt-spinning in the form of ribbons. Its magnetic properties have been investigated via superconducting quantum interference device magnetometry and its magnetic phase diagram was established. Hysteresis and temperature-dependent magnetization measurements show the occurrence of a reentrant spin-glass behavior on cooling. With increasing applied field, the spin-freezing temperature decreases and disappears at very high field, and the Curie temperature increases, broadening the temperature range of the ferromagnetic state. The resulting magnetocaloric effect was evaluated and compared to other interesting magnetic refrigerant materials.

Structure and magnetic properties of the C14 Laves phase (Fe 1− xMn x) 2Nb intermetallics

X-ray diffraction and DC magnetization have been used to investigate the magnetic properties of the (Fe 1− x Mn x ) 2Nb intermetallics with the Nb content kept fixed. The hexagonal C14 Laves phase (space group P6/ mmc) is found in all the studied alloys coexisting with a tetragonal phase ( P4/ mmm) which increases in proportion with the Mn content. The unit cell volume exhibits a parabolic behavior for the hexagonal phase, while steadily growing with the increase of the Mn concentration. At low temperatures the onset of a ferromagnetic ordering has been observed in the Laves phase. The Curie temperature attains a maximum (60 K) for a cell volume of 161.21 Å 3. The tetragonal phase shows ferromagnetism above x = 0.33 with a Curie temperature that increases with the Mn content. Antiferromagnetic correlations have been detected in both structures within the studied composition range, coexisting with ferromagnetism. At low Mn concentration a competition mechanism between ferromagnetic and antiferromagnetic spin correlations leads to frustrated couplings ending in a re-entrant spin-glass like behavior at low temperature. At 4.2 K the Mn-richer alloys exhibit a superconducting behavior.

Phase transition and extended X-ray absorption fine structure of melt-spun amorphous Fe 100−xY x alloys

The phase diagram and local structure of melt-spun amorphous (a-) Fe 100− x Y x (22⩽ x⩽62) alloys were investigated using AC and DC magnetic and extended X-ray absorption fine structure (EXAFS) measurements. The a-Fe–Y system shows reentrant spin glass (RSG) behavior for 42⩽ x⩽58 and spin glass (SG) behavior for 60⩽ x. Two SG transition temperatures, T g and T f, were obtained in the RSG state. The T g, T f and Curie temperature T C decrease with increasing x, and the T C and T g vanish at x=60. A new magnetic phase diagram for the melt-spun a-Fe 100− x Y x alloys was obtained from magnetic measurements for higher Y concentration. The magnetic states of the a-Fe 100− x Y x alloys change remarkably around x=60 and an EXAFS study revealed that the average atomic distance between nearest-neighboring Fe atoms changes at approximately x=60.

Spin-glass-like ordering in ɛ-Fe 3− xNi xN (0.1 ≤ x ≤ 0.8) nanoparticles

ɛ-Fe 3− x Ni x N (0.1 ≤ x ≤ 0.8) nanoparticles are investigated for the magnetic interaction effects at low temperatures. The reduction of saturation magnetization ( σ s) values is attributed to spin pairing effects and surface spin canting. In ZFC and FC magnetization curves, the surface spin-glass layer ( T f1) and the reentrant spin-glass behavior ( T f2) are evidenced below 27 and 22 K respectively. The surface spin-glass phase is described by the random-field model of exchange anisotropy. Based on this theory, a surface spin-glass layer about 8 nm thick is determined. The reentrant spin-glass behavior occurs due to the disorder created by Ni substitution and is observed for 0.2 ≤ x ≤ 0.4. The spin-glass-like ordering in the representative ɛ-Fe 2.6Ni 0.4N system is verified using spin relaxation dynamics and ac susceptibility measurements. The dynamic scaling analysis, based on imaginary part of the ac susceptibility data, gives the parameters τ 0 = 10 −8 s, T c = 15.3 K, and zν = 4.5 and hence confirm the spin-glass-like ordering in ɛ-Fe 3− x Ni x N (0.1 ≤ x ≤ 0.8) nanoparticles.

Cr-doping-induced phase separation and MR effect in the manganite Pr0.5Ca0.5Mn1−xCrxO3 system

Systematic study on magnetic and electrical transport properties has been performed on the Cr-doped Pr0.5Ca0.5Mn1−xCrxO3 (x=0, 0.03, 0.05, 0.07, 0.10) system. The results show that Cr-doping leads to melting of the charge ordering and induces phase separation. For the sample x=0.10, reentrant spin glass behavior is observed and the slowing down model is applicable. The reentrant spin glass behavior and the phase coexistence of charge ordering (CO) and the ferromagnetic metal phase (FMM) are responsible for the changing magnetoresistance effect of the system. The phase separation or coexistence of the CO and FM phase induced by Cr-doping plays an important role in the low temperature properties for the system.

Distinguishable reentrant spin-glass behavior induced by the frustration of exchange interaction in phase-separatedSm0.5(Ca,Sr)0.5MnO3systems

In order to understand the relationship between the stability of the charge-ordered state and the low-temperature phase competition, the magnetic and electrical properties are systemically investigated for half-doped ${\mathrm{Sm}}_{0.5}{A}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$ systems with a dissimilar average $A$-site cationic radius of Ca and Sr, which induces a complete different magnetic ordering and the complex coexistence of magnetic phases at the lower temperature. Some abnormal phenomena are observed in both systems. The frequency dependence of ac magnetization and the bifurcation between zero-field-cooled and field-cooled magnetization curves indicate the reentrant spin-glass behavior in both oxides, which may be induced by the frustration of the ferromagnetic double-exchange interaction and antiferromagnetic superexchange interaction. A long-time relaxation of magnetization is possibly due to the cluster-type and traditional reentrant spin-glass transition. The difference between the behaviors of these two series proves the existence of two types of reentrant spin glass.

A study of [formula omitted] alloys: Structural and magnetic properties

The Fe 2 + x Mn 1 - x Al alloys were studied experimentally to assess the effect of variations of composition around stoichiometric on the structural and magnetic properties of this system. The results indicate that the ordered L 2 1 ( X 2 YZ ) structure of full Heusler alloys can be stabilized with small deviations of composition from the stoichiometric 2:1:1. The saturation magnetization is strongly composition dependent and decreases with the increase of the Mn concentration, in spite of the fact that the Mn atoms carry the largest moment in the ordered phase. The highest Curie temperature was observed for the Fe-richer alloy. Magnetic measurements suggest that atomic disorder and competition of the antiferromagnetic Fe–Mn and Mn–Mn interactions with the ferromagnetic Fe–Fe, Mn–Mn and Fe–Mn interactions lead to a frustrated couplings ending in a reentrant spin-glass behavior at low temperature.

Spin glass state in [formula omitted] polycrystal

The spin glass Fe 0.5 Ni 0.5 TiO 3 has been studied by DC/AC susceptibility as well as Mössbauer spectroscopy measurements. The data show a transition from a paramagnetic to an antiferromagnetic state at T N = 116 K and a reentrant spin-glass behavior is observed below T RSG = 60 K .

Re-entrant spin-glass behaviour in CeAu2Si2

Abstract We present the results of ac and dc susceptibility, magnetic relaxation, specific heat and electrical resistivity measurements on a well-annealed tetragonal ThCr 2 Si 2 -type compound CeAu 2 Si 2 . These data provide clear evidence for the formation of spin glass state in this system at about T f ∼ 2.2 K much lower than its Neel temperature T N = 10 K. The mechanism of the observed re-entrant spin-glass behaviour in CeAu 2 Si 2 is discussed by comparing the present results with those reported for the analogue compounds URh 2 Ge 2 and PrAu 2 Si 2 .

Structural, magnetic and Mössbauer spectroscopic investigations of the magnetoelectric relaxor Pb(Fe 0.6W 0.2Nb 0.2)O 3

The complex perovskite lead iron tungsten niobium oxide, Pb(Fe 0.6W 0.2Nb 0.2)O 3 (PFWN) which belongs to the class of disordered magnetoelectrics, has been studied by X-ray and neutron powder diffraction, magnetic and Mössbauer spectroscopic measurements. Structural, dielectric and magnetic properties of PFWN are presented and reviewed. Magnetic measurements indicate that the most important interactions are of antiferromagnetic nature yielding T N = 300 K, however, with indications of a reentrant spin glass behaviour below 20 K. The parameters of Mössbauer spectra also support the existence of the magnetic order and are consistent with the presence of high-spin Fe 3+ cations located in the octahedral B-site. Rietveld refinements of diffraction data at different temperatures between 10 and 700 K have been carried out. The long-range structure of PFWN is cubic (space group Pm−3 m) over the whole temperature interval. The Fe, W and Nb cations were found to be disordered over the perovskite B-sites. The Pb cations show a position disorder along the 〈111〉 direction shifting from their high-symmetry position. At the temperatures below T N, an antiferromagnetic arrangement of the magnetic moments of Fe 3+ cations in the B-site is proposed in accordance with the antiferromagnetic properties of PFWN. The factors governing the observed nuclear and magnetic structures of PFWN are discussed and compared with those of pure Pb(Fe 0.67W 0.33)O 3, Pb(Fe 0.5Nb 0.5)O 3 and other quaternary Pb-based perovskites containing iron.

Re-entrant spin-glass behaviour of geometrically frustratedSrFe3(PO4)3O

Four anomalies of magnetic origin were observed atT1 = 10.7 K,T2 = 11.7 K,Tf = 22.4 K,and Tc = 23.5 K in SrFe3(PO4)3O with a geometrically frustrated magnetic lattice using different techniques.SrFe3(PO4)3O shows features typical of re-entrant spin glass with the freezing temperatureTf in zero static magnetic field and the Curie temperatureTc.These features are the sharp upturn of the dc magnetization and ferromagnetic hysteresis loops on theM(H) curvesbelow Tc, frequency-dependent rounded maxima on both theχ′(T) and χ′′(T) curves at different positions, a very small anomaly of specific heat atTf, and strong suppression of spin-glass behaviour by magnetic fields above0.1 T. High-field magnetization measurements revealed the existence of a1/3-magnetizationplateau above 25 T at T = 1.7 K. Magnetic reflections were observed belowTc on neutron powder diffraction patterns. Additional magnetic reflections appeared belowT2.

Structural study of the re-entrant spin-glass behaviour of Fe–Al alloys

Neutron powder diffraction measurements were performed on Fe 70Al 30 alloy in order to determine the relationship between the magnetic behaviour and the structural changes observed in this alloy. Results show that the re-entrant spin-glass behaviour is linked with D03 structure. There is a strong correlation between the lattice parameter and the diffraction peak intensity and all the magnetic changes reported in literature can be explained in terms of this relationship. Finally, magnetovolume effects similar to invar effect are reported in the spin-glass phase.