Shows Spin Glass Behavior Research Articles

Electronic comprehension of exchange bias effect in Sr2CoRuO6−δ thin-film

Sr2CoRuO6 in its bulk form shows spin glass behavior with a transition temperature of 95 K, and in its epitaxial thin film, it shows similar behavior with a transition temperature of 135 K. We have studied the structural, electronic, and magnetic properties of a polycrystalline thin film of oxygen-deficient Sr2CoRuO6−δ (SCRO), which shows ferrimagnetic or glassy behavior up to room temperature. The presence of oxygen deficiency causes multivalent cations Co3+ and Co2+ and Ru4+ and Ru5+, which introduces various kinds of magnetic interactions between Co3+–O–Co2+, Co3+–O–Ru4+, Co2+–O–Ru4+, Co3+–O–Ru5+, and Co2+–O–Ru5+ exchange paths, producing unusual exchange bias effects in the single layer thin film of SCRO. The interionic charge transfer between Co and Ru ions as a result of the negative charge transfer energy of the system helps in visualizing the unconventional exchange bias effect in the system.

Structural characterization and magnetic properties of iron-phosphate glass prepared by sol-gel method

The relationship between the local structure and magnetic properties of iron phosphate glass xFe2O3 • (100-x) P2O5 abbreviated as xFeP prepared by a sol-gel method has been investigated. From the Mössbauer spectroscopy results, it was found that iron ions are present in FeIII(distorted octahedral) and FeII(octahedral) coordination. HAADF-STEM images and elemental mapping results revealed that iron and phosphorus are uniformly dispersed in the system. It is clear from the magnetic susceptibility results that only 50FeP glass heat-treated at 200°C shows spin glass behavior and all other glasses are superparamagnetic at low temperatures. The Weiss temperatures (θw) obtained for all the glasses were negative, suggesting that the interaction between the magnetic moments is antiferromagnetic. In these samples, the higher the proportion of FeIII ions, the higher the frustration of the entire system is. The [FeIII] / [Fetotal] molar ratio decreases as the heat-treatment temperature increased.

Room temperature magnetism in zinc nano ferrite synthesized by a novel oxalate-ceramic method

Zinc nano-ferrite has been synthesized using a novel oxalate-ceramic method and its magnetic properties are reported in this paper. The hysteresis loop recorded at 300 K exhibits ferrimagnetic behavior. The Neel temperature was found to be 557 K. The AC susceptibility curve also indicates ferrimagnetic behavior. The temperature dependent magnetization curves, obtained in the temperature range of 4–300 K, show spin glass behavior. Using this method of synthesis large quantity of ferrite can be synthesized therefore this method can become useful technique for industrial scale production.

Observation of Spin-Glass Behavior in La0.85Sr0.15CoO3 Single Crystals

The magnetic behavior of La0.85Sr0.15CoO3 single crystals and polycrystals has been subjected to a controversial debate for the last several years; while some groups show evidence for phase separation, others show spin-glass (SG) behavior. Here, we present a comprehensive investigation of the structural, ac susceptibility, and dc magnetization properties of La0.85Sr0.15CoO3 single crystals grown by float zone method. The structural analysis of XRD data by Rietveld refinement reveals the single crystallographic phase. The ac susceptibility results exhibit a frequency dependent peak shift (∼2 K) and time-dependent memory effect below the freezing temperature. The characteristic time scale τo calculated from this peak shift is found to be of ∼10−13 s which matches very well with typical values observed for a SG system. Further, the peak shift of the zero-field-cooling curves to lower temperature at higher dc fields is well described by the well-known de Almeida Thouless line, a characteristic of SG behavior. Thus, all our experimental findings confirm the existence of SG behavior in La0.85Sr0.15CoO3 single crystals.

Loss of spin glass behavior in ultrathin AuFe films

We determined the temperature dependence of the magnetization of thin ${\text{Au}}_{97}{\text{Fe}}_{3}$ films in the thickness range between 1 and 50 nm by performing polarized neutron reflectivity measurements in a magnetic field of 6 T in a temperature range from 200 down to 2 K. For the films in the thickness range from 50 to 2 nm, we observed a Brillouin-type behavior of noninteracting Fe atoms down to 50 K followed by a strong reduction compared to the Brillouin curve below 50 K. This reduction in the magnetization is a measure of the spin glass frustration and depends on the film thickness below 20 nm as shown in our previous study [M. Saoudi, H. Fritzsche, G. J. Nieuwenhuys, and M. B. S. Hesselberth, Phys. Rev. Lett. 100, 057204 (2008)] on ${\text{Au}}_{97}{\text{Fe}}_{3}$ films. The present study is a continuation of this work extending the thickness range down to 1 nm. It shows that below 10 nm, the reduction in the spin glass magnetization compared to a Brillouin-type behavior decreases with decreasing film thickness. Finally, the magnetization of the 1-nm-thick film could be described with a Brillouin function also below 50 K proving that ultrathin ${\text{Au}}_{97}{\text{Fe}}_{3}$ layers below 1 nm do not show spin glass behavior anymore but are paramagnetic.

A hybrid cobalt hydroxyacetate magnet: ionothermal synthesis, 3-D Co–O–Co connectivity and spin glass behavior

An ionothermal reaction has generated a cobalt hydroxyacetate magnet that contains a three-dimensional Co-O-Co framework consisting of vertex-sharing octahedral chains bridged by another octahedra via edge-sharing and shows spin glass behavior.

The incongruous observation of magnetic phase separation in La0.85Sr0.15CoO3 spin glass system

Phase separation (PS) in hole-doped cobaltites (La1−xSrxCoxO3) is drawing renewed interest recently. In particular, the magnetic behavior of La0.85Sr0.15CoO3 has been subjected to a controversial debate for the past several years; while some groups show evidence for magnetic PS, others show spin glass (SG) behavior. Here, an attempt is made to resolve the controversy related to “PS versus SG” behavior in this compound. We present the results of a comprehensive investigation of the dc magnetization, ac susceptibility, and the magnetotransport properties of La0.85Sr0.15CoO3 samples. We contemplate that the magnetic PS in La0.85Sr0.15CoO3 is neither intrinsic nor inherent, but it is a consequence of the preparation conditions. It is realized that a low temperature annealed (LTA) sample shows PS whereas the high temperature annealed (HTA) sample shows SG behavior. The Brillouin-like behavior of field cooled dc magnetization and apparently no frequency dependent peak shift in ac susceptibility for the LTA sample characterize it to be of ferromagneticlike whereas a kink in field cooled dc magnetization and a considerable amount (∼3 K) of frequency dependent peak shift in the ac susceptibility for the HTA sample characterize it to be of SG state. The magnetotransport properties show that the HTA sample is more semiconducting as compared to the LTA sample. This is interpreted in terms of the presence of isolated as well as coalescing metallic ferromagnetic clusters in the case of LTA sample. The magnetoresistance (MR) at 10 K for the HTA sample exhibits a huge value (∼65%) as compared to the LTA sample, and it monotonically decreases with the rise in temperature. Such a high value of MR in the case of HTA sample is strongly believed to be due to the spin dependent part of random potential distribution. Further, the slow decay of remnant magnetization with progress of time and the existence of hysteresis at higher temperatures (up to 200 K) in the case of LTA sample as compared to the HTA sample clearly unveil different magnetic states associated with them.

Cyanide-Bridged FeIII−MnIII Bimetallic Complexes with Dimeric and Chain Structures Constructed from a Newly Made mer-Fe Tricyanide: Structures and Magnetic Properties

Four cyanide-linked Fe(III)-Mn(III) complexes were prepared by reacting Mn Schiff bases with a new molecular precursor (PPh(4))[Fe(qcq)(CN)(3)] [1; qcq = 8-(2-quinolinecarboxamido)quinoline anion]. They include a dimeric molecule, [Fe(qcq)(CN)(3)][Mn(3-MeOsalen)(H(2)O)] x 2 H(2)O [2 x 2 H(2)O; 3-MeOsalen = N,N'-ethylenebis(3-methoxysalicylideneiminato) dianion], and three 1D zigzag chains, [Fe(qcq)(CN)(3)][Mn(5-Clsalen)] x 3 H(2)O [3 x 2 MeOH; 5-Clsalen = N,N'-ethylenebis(5-chlorosalicylideneiminato) dianion], [Fe(qcq)(CN)(3)][Mn(5-Brsalen)] x 2 MeOH [4 x 2 MeOH; 5-Brsalen = N,N'-ethylenebis(5-bromosalicylideneiminato) dianion], and Fe(qcq)(CN)(3)][Mn(salen)].MeCN x H(2)O [5 x MeCN; salen = N,N'-ethylenebis(salicylideneiminato) dianion]. The complexes consist of extensive hydrogen bonding and pi-pi stacking interactions, generating multidimensional structures. Magnetic studies demonstrate that antiferromagnetic couplings are operative between Fe(III) and Mn(III) centers bridged by cyanide ligands. On the basis of an infinite chain model, magnetic coupling parameters of 2-5 range from -9.3 to -14.1 cm(-1). A long-range order is observed at 2.3 K for 3 and 2.2 K for 4, while compound 5 shows spin glass behavior possibly coupled with magnetic ordering.

Crystal structure and magnetic state of U 2XSi 3 (X = Fe, Pt)

Atomic arrangement in U 2XSi 3 with X = Pt and Fe was investigated by electron diffraction and X-ray powder diffraction and discussed in conjunction with the results of magnetic susceptibility, magnetization, specific heat electrical resistivity measurements. U 2PtSi 3 crystallizes in the simple AlB 2-type structure, where Pt and Si atoms are located at B sites disorderly and shows spin glass behavior at low temperature. Contrarily, the electron diffraction pattern for U 2FeSi 3 reveals a superstructure doubling the lattice parameter as that observed for U 2RuSi 3, suggesting absence of the random structure. In this structurally ordered compound U 2FeSi 3, no spin glass behavior is detected.

One-dimensional ferromagnetism of gaudefroyiteCa4(MnO)3(BO3)3CO3

The structure of gaudefroyite, ${\mathrm{Ca}}_{4}{(\mathrm{Mn}\mathrm{O})}_{3}{(\mathrm{B}{\mathrm{O}}_{3})}_{3}\mathrm{C}{\mathrm{O}}_{3}$, is built up of linear chains of edge-shared $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedra which are interconnected via $\mathrm{B}{\mathrm{O}}_{3}$ groups to form a Kagom\'e lattice in the $ab$ plane. Magnetic measurements show that the Mn moments along the chain are ferromagnetically coupled, but frustration exists between the chains because of the triangular arrangement of the Mn ions within the $ab$ plane. Over a large temperature range, $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}\ensuremath{\leqslant}T\ensuremath{\leqslant}320\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the magnetic properties of this compound can be described by the classical Heisenberg spin chain model with a single ion anisotropy modification, $H=\ensuremath{-}2J\ensuremath{\sum}{S}_{i}{S}_{i+1}+D\ensuremath{\sum}{S}_{iz}^{2}$, with $J=4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $D=0.67\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Below $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the moments are effectively constrained to the $ab$ plane and the magnetization with ${\mathrm{H}}_{0}\ensuremath{\Vert}ab$ shows spin glass behavior. No indication of magnetic ordering has been observed down to $1.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Superparamagnetic and spin glass behavior in mesoporous niobium oxide bis(cyclopentadienyl)nickel composites

Herein we report the synthesis and characterization of a new family of mesoporous niobium oxide bis(cyclopentadienyl)nickel composites which exhibit superparamagnetic or spin glass behavior depending on the different loading levels of the organometallic in the pores. XRD and nitrogen adsorption studies confirm the retention of the mesostructure in these new materials upon introduction of the guest species. The Nb 3d region of the XPS provides evidence for the slight reduction of the Nb(V) oxide walls while the Ni 2p region shows the presence of both neutral and cationic bis-cyclopentadienyl nickel species with peaks at 856.3 eV and 861.9 eV respectively, as well as two more highly oxidized species at 865.5 eV and 867.3 eV. The presence of neutral and cationic bis(cyclopentadienyl)nickel is further confirmed by EPR. SQUID magnetic measurements show superparamagnetic behavior for the material with a Ni∶Nb ratio of 0.07∶1, while at a ratio of 0.1∶1 the material shows spin glass behavior, a phenomenon normally associated with amorphous metal alloys. The difference in magnetic behavior is rationalized by an increased density of unpaired spins in the pore structure.

Spin glass behavior in some Fe–Mn–Al disordered alloys

In this work, we report an ac susceptibility study of Fe0.5Mn0.2Al0.3, Fe0.5Mn0.1Al0.4, and Fe0.225Mn0.375Al0.40 disordered alloys. All the samples exhibit only one well defined peak near 58, 18, and 31 K, respectively. When the frequency of the ac field increases, the measured intensities of the peaks decrease and the maxima shift to higher temperatures, and when the dc field increases the intensity of the peaks decreases. This dependence of the position and intensity of the peaks on the field and frequency is evidence of the spin glass character of the transitions in these alloys. Mössbauer spectra at different temperatures were performed for the sample with 30 at. % Al and the plot of the adjusted mean hyperfine field versus temperature shows a kink at 53 K which is further evidence that this sample shows spin glass behavior.

LaSrCrxNi1-xO4+δ: Crystal Chemistry, Magnetism, and the Stabilization of NiI in an Oxide Environment

Magnetic, structural and reduction data on the K2NiF4 structure CrIII/NiIII oxides, LaSrCrxNi1-xO4+δ (0.1 ≤ x ≤ 0.9, where δ may be negative) are reported; samples with x > 0.2 adopt the tetragonal I4/mmm space group, while for x ≤ 0.2, the samples are multiphasic due to competition between a novel vacancy-ordered Immm structure and the undistorted K2NiF4 phase. Magnetic studies in the temperature range 5 ≤ T/K ≤ 300 show spin glass behavior for x < 0.9, with freezing temperatures of between 12 and 16 K: at higher temperature the susceptibilities display Curie−Weiss behavior. The magnetism of the x = 0.9 sample resembles that reported for LaSrCrO4, displaying an antiferromagnetic transition at 150 K and weak ferromagnetism below 130 K. Reduction of the title compounds in 1 atm of flowing H2 at ∼500 °C produces stable, oxygen-deficient compounds, notably La2Sr2CrNiO7, which contains NiI with a thermal stability unprecedented in an oxide.

Low-field magnetization in compounds of the modified pyrochlore structure CsM 12+M 3+2F 6

The magnetization in single crystalline samples of CsNiFeF 6, CsCoFeF 6, and CsCoCrF 6, all with the modified pyrochlore structure, is investigated with a superconducting quantum interference device magnetometer at low temperatures. The range of the magnetic field is between 1 G and 200 G. All compounds show spin glass behavior with a cusp temperature around 4 K. The temperature of the spin glass cusp rises with rising magnetic field and this dependency can be approximated by a power law. A variation of cooling and heating rates between 100 s/K and 10000 s/K in the spin glass phase of CsNiFeF 6 shows not only the well known time dependencies of the zero field cooled curve, but also a downward shift in the field cooled curve up to 5 percent at slow rates, indicating a single ground state in the spin glass phase.

Spin glass behavior of Cd1−xMnxTe below the nearest-neighbor percolation limit

Magnetization measurements down to 10 mK of Cd1−xMnxTe for Mn concentrations 0.01≤x≤0.15 show spin glass behavior. Such behavior is attibuted to short-range exchange and dipolar interactions. Both interactions are used to explain the concentration dependence of the spin freezing temperatures for 0.01≤x≤0.6, the short-range exchange dominating at high concentrations, and the dipolar interaction at low concentrations.

Magnetic phase diagram of Cd1−xMnxSe below the nearest neighbor percolation limit

Abstract Magnetization measurements down to 10 mK of Cd1−xMnxSe at Mn concentrations below the nearest-neighbor percolation limit show spin glass behavior. The previously accepted phase diagram is revised, showing a x2 dependence at low x. Such behavior is attributed to neighbors further than nearest-neighbors and Bloembergen-Rowland type of indirect exchange.

Magnetism of V-doped Ti2O3

Abstract Adding V-atoms introduces localized spins in Ti2O3. The NMR frequency shift of 51V does not follow the susceptibility, which might suggest that V atom is nonmagnetic. The NMR absorption intensity decreased with increasing V concentration. At low temperatures, V-doped Ti2O3 shows spin glass behavior.