Reentrant Spin Glass Transition Research Articles

Reentrant spin glass transition and partial substitution induced superconductivity in magnetocaloric Mn5Sn3 alloys

Reentrant spin glass transition and partial substitution induced superconductivity in magnetocaloric Mn5Sn3 alloys

Effects of 4d transition metal Pd doping on the magnetic and superconducting properties of 112-type iron pnictide EuFeAs2

The recently discovered 112-type EuFeAs2 compound that shows complex Eu-spin magnetism provides a new platform to study the interplay between superconductivity (SC) and magnetism in iron pnictide superconductors. In this paper, by substituting Fe with the 4d transition metal (TM) Pd, we have synthesized a series of EuFe1−x Pd x As2 (0 ⩽ x ⩽ 0.08) samples and studied the doping effect on SC and magnetism by means of electrical transport and magnetization measurements. The systematic evolution of the lattice parameters indicates that the Pd atoms have been successfully substituted into the Fe sites. With Pd doping, the Fe-related spin density wave transition at in the parent phase is rapidly suppressed, and SC simultaneously emerges, exhibiting a domelike shape with a maximum onset transition temperature of around 18.5 K at x = 0.04. On the other hand, the Eu-related antiferromagnetic order at is suppressed very slowly and persists up to x = 0.08, covering the whole SC dome region. Also, the reentrant spin-glass and spin-reorientation transitions below remain unchanged with Pd doping. All these results indicate that the Eu spins have little effect on SC in EuFe1−x Pd x As2. Finally, based on the resistivity and magnetization data, the T − x phase diagram of EuFe1−x Pd x As2 is constructed and compared with those of 3d TMs Co/Ni and La doped ones.

Experimental study of multiple magnetic transitions in micrometer and nano-grain sized Ni3TeO6-type oxide

We report the experimental results of dc and ac magnetic susceptibility (χdc and χac) and specific heat (CP) measurements of the powdered Ni3TeO6-type oxide. Upon decreasing the grain size from micrometer (bulk) to nanometer range, the magnetic measurements have indicated multiple transitions, viz., a cusp at paramagnetic to ferrimagnetic (FIM) transition temperature (TC) ∼ 78 K, an antiferromagnetic (AFM) transition temperature (TN) ∼ 52 K, and a re-entrant spin glass (RSG) transition at Tm2 ∼ 7.49 K. The ferrimagnetic transition temperature TC is found to be highly sensitive to dc magnetic fields, where superposition of a small dc field (10 Oe) in the ac susceptibility measurement or the application of a dc magnetic field of up to 100 Oe in the dc magnetic measurement is enough to suppress the observed TC at 78 K. The CP(T) measurement also revealed a RSG state at lower temperatures for the sample with nano-sized grains. The absence of any sharp peak at TC in the CP(T) curves implies the absence of a true long-range FIM spin order in the samples. The coexistence of a RSG state with multiple magnetic transitions is understood as an effect of competitive AFM and FIM phases in the Ni3TeO6-type structure.

Production and structural and magnetic characterization of copper oxide nanocrystals with large Fe contents

In this work it was studied the influence of large quantities of iron in the structural and magnetic properties of copper oxide nanoparticles, which were produced by the co-precipitation method. The samples studied were those of the (Cu1 − xFex)O system, with x = 0.20, 0.25, and 0.30. The concentrations of the precipitating agent were 7 and 8 M, and with variable calcination temperature. Based on the Rietveld refinement of the X-ray diffraction patterns, all the samples were found to have only the CuO monoclinic structure with a C2/c space group. In addition, it was found that the mean crystallite size varies between 39 and 59 nm, and that the substitution of Cu by Fe atoms occurs along the a-axis. By SEM measurements, it was detected that the particles are present as agglomerates. Previous work reported for the sample with x = 0.15, and prepared by co-precipitation [1], proved that the obtained particles are of nanometer size. The zero field cooling (ZFC) and field cooling (FC) curves, obtained by vibrating sample magnetometer (VSM), showed a peak at 97 K, which was also detected for a sample with x = 0.15, which corresponds to a reentrant spin-glass transition [1].

Large anisotropic magnetocaloric effect in ferromagnetic semimetal PrAlSi

We report on the large anisotropic magnetocaloric effect of PrAlSi, a ferromagnetic semimetal of current interest with a probable topologically nontrivial electronic structure. The maximum magnetic entropy change amounts to −ΔSM=22.6J/kgK near the Curie temperature TC=17.8K under a magnetic field change of μ0ΔH=5T along the magnetic easy c axis. A highly relevant feature is the small crystalline electric field splitting of the Pr3+ (J=4) multiplet, which appears to be comparable with the effective exchange interaction in the magnetic ordering. This leads to the full saturation moment of the Pr3+ ion in small fields and an accumulation of magnetic entropy in the vicinity of the magnetic ordering. The weakly first-order nature of the ferromagnetic transition and the subsequent reentrant spin-glass transitions below TC are features further enhancing the magnetocaloric effect. Given the strong magnetic anisotropy, a large rotating magnetocaloric effect becomes achievable in this material.

Coexistence of long-range cycloidal order and spin-cluster glass state in the multiferroic BaYFeO4

We report the presence of spin glass state below the cycloidal spin ordering in the multiferroic BaYFeO4. This compound is known to crystallize in an orthorhombic structure with a centrosymmetric space group Pnma and exhibits two successive antiferromagnetic phase transitions. Upon cooling, it undergoes a spin density wave (SDW)-like antiferromagnetic ordering at TN1 ~ 48 K and a cycloidal ordering at TN2 ~ 35 K. Using dc magnetic memory effect and magnetization relaxation studies, we have shown that this oxide undergoes a reentrant spin glass transition below T* ~ 17 K. Our analysis suggests the presence of spin clusters in the glassy state. The coexistence of spin-cluster glass and long-range cycloidal ordered states results in an exchange bias effect at 2 K. The origin of the glassy state has been attributed to freezing of some Fe3+ moments, which do not participate in the long-range ordering.

Re-entrant spin glass transitions: new insights from acoustic absorption by domain walls

Re-entrant spin glass (RSG) transitions in Ni-Mn and Au-Fe have been reassessed by acoustic measurements of the magneto-mechanical damping by domain walls. Stress-induced non-thermally activated domain wall dynamics is progressively replaced by an intense thermally activated relaxational response when the temperature approaches the RSG freezing point. A “frozen” state with negligible motion of domain walls on atomic and mesoscopic scales occurs in the RSG. We propose that RSG freezing has its origin in intrinsic properties of domain walls.

Effects of Cu doping on the electronic structure and magnetic properties of MnCo2O4 nanostructures

Reported here are the results and their analysis from our detailed investigations of the effects of Cu doping () on the electronic structure and magnetic properties of the spinel O4. A detailed comparison is given for the and cases for both the bulk-like samples and nanoparticles. The electronic structure determined from x-ray photoelectron spectroscopy and Rietveld analysis of x-ray diffraction patterns shows the structure to be: ()A]B i.e. substitutes for on the octahedral B-sites. For the bulk samples, the ferrimagnetic K for is lowered to K for the sample, this decrease being due to the effect of Cu doping. For the nanosize () sample, the lower K ( K) is observed using analysis, this lowering being due to finite size effects. For , fits of dc paramagnetic susceptibility data of versus T in nanosize samples to the Néel expression are used to determine the exchange interactions between the A and B sites with exchange constants: K (4.1 K), K (16.3 K) and K (13.8 K) for . The temperature dependence of ac susceptibilities and at different frequencies shows that in bulk samples of and , the transition at TC is the normal second order transition. But for the nanosize and 0.2 samples, analysis of the ac susceptibilities shows that the ferrimagnetic transition at TC is followed by a re-entrant spin-glass transition at lower temperatures K (138 K) for (). Analysis of the ac susceptibilities, and , versus T data is done in terms of two scaling laws: (i) Vogel–Fulcher law ; and (ii) power law of critical slowing-down . These fits confirm the existence of glassy behavior below TSG with the parameters (8.91), (9.6 × 10) and K (∼138 K) for the samples (0.2), with similar results obtained for other samples. The linear behavior of the peak maximum in versus (AT-line) further supports the existence of glassy states in nanosize samples. For , the temperature and composition dependence of the hysteresis loop parameters are investigated; all the samples with x ⩾ 0.1 have the coercivity HC and remanence . Since the results reported here in these nanostructures are significantly different from those in bulk , further investigations of their magnetic structures using neutron diffraction are warranted.

Effects of pressure and magnetic field on the reentrant superconductor Eu( Fe0.93Rh0.07)2As2

Electron-doped Eu(Fe$_{0.93}$Rh$_{0.07}$)$_2$As$_2$ has been systematically studied by high pressure investigations of the magnetic and electrical transport properties, in order to unravel the complex interplay of superconductivity and magnetism. The compound reveals an exceedingly broad re-entrant transition to the superconducting state between $T_{\rm{c,on}} = 19.8$ K and $T_{\rm{c,0}} = 5.2$ K due to a canted A-type antiferromagnetic ordering of the Eu$^{2+}$ moments at $T_{\rm{N}} = 16.6$ K and a re-entrant spin glass transition at $T_{\rm{SG}} = 14.1$ K. At ambient pressure evidences for the coexistence of superconductivity and ferromagnetism could be observed, as well as a magnetic-field-induced enhancement of the zero-resistance temperature $T_{\rm{c,0}}$ up to $7.2$ K with small magnetic fields applied parallel to the \textit{ab}-plane of the crystal. We attribute the field-induced-enhancement of superconductivity to the suppression of the ferromagnetic component of the Eu$^{2+}$ moments along the \textit{c}-axis, which leads to a reduction of the orbital pair breaking effect. Application of hydrostatic pressure suppresses the superconducting state around $14$ kbar along with a linear temperature dependence of the resistivity, implying that a non-Fermi liquid region is located at the boundary of the superconducting phase. At intermediate pressure, an additional feature in the resistivity curves is identified, which can be suppressed by external magnetic fields and competes with the superconducting phase. We suggest that the effect of negative pressure by the chemical Rh substitution in Eu(Fe$_{0.93}$Rh$_{0.07}$)$_2$As$_2$ is partially reversed, leading to a re-activation of the spin density wave.

Reentrant spin glass behavior and magnetodielectric coupling of an Ir-based double perovskite compound, La2CoIrO6.

The structural, magnetic, electrical and dielectric properties of an Ir-based double perovskite compound, La2CoIrO6, have been investigated. The sample undergoes a paramagnetic-ferromagnetic transition at TC, followed by a reentrant spin-glass transition at lower temperatures. The reentrant spin glass state in La2CoIrO6 is associated with the competitions of the antiferromagnetic coupling between Ir4+ and Co2+ ions and the ferromagnetic clusters. La2CoIrO6 shows a semiconducting transport behavior in the temperature range 65 to 360 K and the transport behavior can be well described by the three-dimensional Mott variable range hopping conduction mechanism. Moreover, a strong frequency dependence of dielectric constant behavior for La2CoIrO6 is observed and the dielectric relaxation can be ascribed to the electron hopping between different transition metal ions. In addition, the isothermal magnetic field dependent dielectric constant measurements show that a clear magnetodielectric coupling effect exists in La2CoIrO6 at low temperatures.

Effect of temperature and magnetic field on magnetomechanical damping of Fe-based bulk metallic glasses

Temperature and magnetic field dependence of magnetomechanical damping (MMD) of two ferromagnetic Fe-based bulk metallic glasses with different Curie temperatures, TC, have been studied over a broad temperature interval from the para-ferromagnetic transition down to 15 K. The damping has been scanned under periodic magnetic field at certain preselected temperatures in the ferromagnetic and paramagnetic phases. The selection of bulk metallic glasses for investigations allowed us to eliminate all dislocation-related anelastic effects and facilitated separation of the MMD components. Under zero field, the non-linear MMD emerges at TC and first increases linearly with (TC − T), then levels off until a maximum is formed at around 36 K. At lower temperatures, the magnetic domain wall related non-linear MMD component is partially or completely supressed, depending on the alloy composition. Qualitatively similar anomaly is found in the temperature dependence of the linear macroeddy current damping. These anomalies in the temperature spectra are concomitant with the emergence of a notable hysteresis in MMD versus periodic field dependences and of a maximum of non-linear MMD close to the position of the macroeddy damping peak. The uncovered phenomena are attributed to abrupt change of magnetic properties of ferromagnetic bulk metallic glasses at low temperatures, presumably due to the re-entrant spin glass transition.

Solid Solutions between BiMnO3 and BiCrO3.

Solid solutions BiMn1-xCrxO3 (0 ≤ x ≤ 1) have been prepared at 6 GPa and 1370-1620 K. Their structural properties have been studied with synchrotron X-ray powder diffraction, and their physical properties have been investigated by dc/ac magnetic, specific heat, dielectric, and differential scanning calorimetry measurements. A magnetic phase diagram of BiMn1-xCrxO3 is established. A phase with orbital ordering observed in BiMnO3 is suppressed at x > 0.1, accompanied by a drop in the ferromagnetic Curie temperature TC from 101 K for x = 0 to 76 K for x = 0.15 and sharp changes in the lattice parameters. The TC value monotonically decreases up to x = 0.3 (with TC = 53 K). For intermediate compositions with x = 0.4, 0.5, spin-glass magnetic properties are found at 28 and 24 K, respectively. The Néel temperature TN linearly increases from 36 K for x = 0.6 to 111 K for x = 1.0. A spin-reorientation transition is observed at 61 K for x = 0.9 and 72 K for x = 1.0. Re-entrant spin-glass transitions are also observed for samples with x = 0.3, 0.6, 0.7 by ac susceptibility at low temperatures. At high temperatures, a structural phase transition from C2/c to Pnma symmetry is observed for all compositions with a monotonic change of the phase transition temperature. The magnetic phase diagram from the BiMnO3-rich side (x ≤ 0.5) resembles a phase diagram of BiMn1-xScxO3 solid solutions, indicating that the nature of substituting cations (magnetic or nonmagnetic) is not crucial for doped BiMnO3.

Capacitive and magnetoresistive origin of magnetodielectric effects in Sm-substituted spiral antiferromagnet BiMnFe2O6

BiMnFe2O6 exhibits a spiral antiferromagnetic ordering below 212 K and a reentrant spin glass transition at 34 K. Further, magnetic and dielectric anomalies occur at the same temperature (T = 170 K) with a significant magnetodielectric effect. Upon substitution of Sm3+ for Bi3+ ions in Bi1−xSmxMnFe2O6 (x = 0.1 and 0.2), the dielectric anomaly shifts to low temperatures (T = 135 and 72 K, respectively), whereas the magnetic anomaly develops into a weak ferromagnetism. For x = 0.2, the weak ferromagnetism occurs in a wide temperature range (90–201 K). Below 90 K, it undergoes a transition to an antiferromagnetic state. In contrast to the parent compound (x = 0), the magnetodielectric effect is observed both in the antiferromagnetic region (T < 90 K) with a maximum at the dielectric anomaly (72 K) and also in the weak ferromagnetic region. It has been shown that the magnetodielectric effect in the antiferromagnetic region has an intrinsic capacitive origin while that observed at the weak ferromagnetic region originates from magnetoresistance.

Structural-modulation-driven spin canting and reentrant glassy magnetic phase in ferromagneticLu2MnNiO6

Unusual behavior of reentrant spin-glass (RSG) compound Lu2MnNiO6 has been investigated by magnetometry and neutron diffraction. The system possesses a ferromagnetic (FM) ordering below 40 K and undergoes a RSG transition at 20 K. Additionally, Lu2MnNiO6 retains memory effect above the glassy transition till spins sustain ordering. A novel critical behavior with unusual critical exponents (beta =similar to 0.241 and gamma similar to 1.142) is observed that indicates a canting in the spin structure below the ferromagnetic transition (T-C). A comprehensive analysis of temperature-dependent neutron diffraction data and first-principles calculations divulge that a structural distortion induced by an octahedral tilting results in a canted spin structure below T-C.

Investigation of structural and temperature dependent electromagnetic properties of Co0.5Zn0.5CrxFe2−xO4

Mixed ferrites with nominal chemical compositions Co0.5Zn0.5CrxFe2−xO4 ranging from x=0 to 0.5 in the steps of 0.1 have been prepared by the standard solid state reaction method. XRD patterns confirm single phase and formation of cubic spinel structure. The lattice constant (a0), average grain size (D) and bulk density (ρB) are decreased with increasing Cr content. The ρB decreases with Cr content due to lighter atomic weight. On the other hand, both D and ρB of each composition increase with increasing sintering temperature (Ts). All samples show reentrant spin glass transition at low temperature in zero field cooled magnetization. The saturation magnetization (Ms) and Néel temperature (TN) decrease with Cr substitution due to weakening the super-exchange interaction. The coercivity (Hc) increases with increasing Cr content for various Co0.5Zn0.5CrxFe2−xO4. It may be attributed to the effect of decreasing D. Frequency dependent initial permeability (μ′i) decreases with increasing Cr content. The Ms and ρB play an important role in changing μ′i. On the other hand, the μ′i for each composition increases with increasing Ts. The highest relative quality factor (Q) is observed for various Co0.5Zn0.5CrxFe2−xO4 sintered at 1573K. The DC electrical resistivity (ρDC) of these samples increases with increasing Cr content due to decreasing Fe3+ ions at B-site.

Low temperature study of mechanically alloyed Fe67.5Ni32.5 Invar sample

The study at low temperatures of powder of the Invar alloy, Fe67.5Ni32.5, produced by mechanical alloying, shows that the sample presents two structural phases, the Fe–Ni BCC and the Fe–Ni FCC. The 57Fe Mössbauer spectra obtained in this sample at different temperatures were fitted considering two hyperfine magnetic field distributions. The first one having the larger mean field and only one peak (at ca. 35T, varying with T), is associated with the BCC phase, and the second one, presenting several broad peaks (distributed between 10 and 35T), is associated to the FCC phase. A singlet, which is associated to low spin Fe sites of the FCC phase, was also considered. The mean hyperfine magnetic field of the BCC phase increases monotonically as temperature decreases, while that of the FCC phase presents an anomaly near 75K. The real part of the ac magnetic susceptibility temperature scans presents a peak whose position increases from 31 to 39K, when the ac field frequency increases from 100 to 5000Hz. These results permit to associate the detected anomaly to the occurrence of a reentrant spin glass transition.

Observation of the second-order magnetic and reentrant spin-glass transitions in LiNi0.5Mn0.5O2

The structure and magnetic properties of LiNi0.5Mn0.5O2 were studied by synchrotron X-ray diffraction, dc and ac susceptibilities. The material showed a continuous magnetic transition from paramagnetism into ferrimagnetism, followed by a spin glass with the decrease of temperature. Using a criterion given by Banerjee to distinguish first-order magnetic transition from second-order ones, it is shown that the ferrimagnetic transition at 108 K belongs to the second-order type. The frequency dependence of peak intensity and the shift in ac susceptibility at 14 K suggest a reentrant spin glass transition in LiNi0.5Mn0.5O2.

Reentrant spin-glass state and magnetodielectric effect in the spiral magnetBiMnFe2O6

The complex oxide $\mathrm{Bi}\mathrm{Mn}{\mathrm{Fe}}_{2}{\mathrm{O}}_{6}$ crystallizing in a centrosymmetric orthorhombic structure ($Pbcm$) is known to exhibit a spiral antiferromagnetic ordering at ${T}_{N}\ensuremath{\sim}212$ K and an anomaly in magnetization at low temperature (${T}_{P}\ensuremath{\sim}34$ K). To understand the origin of the low temperature anomaly and to verify experimentally whether or not the spiral magnetism induces ferroelectricity, we have carried out detailed magnetization and electrical measurements on a polycrystalline sample. Frequency-dependent ac susceptibility, dc magnetic memory effect, and dc magnetization relaxation studies show that the low temperature anomaly at ${T}_{P}$ is associated with a reentrant spin-glass transition. From dc magnetization, we found that there exists another distinct temperature (${T}_{\text{irr}}$), which corresponds to a strong thermomagnetic irreversibility. The field dependence of these two temperatures, ${T}_{P}(H)$ and ${T}_{\text{irr}}(H)$, follow Gabay-Toulouse and de Almeida--Thouless lines, respectively, which are indicative of the Heisenberg spin-glass state. We also observe another magnetic anomaly at ${T}^{*}\ensuremath{\sim}170$ K, where a dielectric anomaly with a significant magnetocapacitance effect is observed. However, pyroelectric current and positive-up-negative-down measurements reveal the absence of ferroelectricity in this compound.

High-pressure synthesis, structural and complex magnetic properties of the ordered double perovskite Pb2NiReO6

The ordered double perovskite Pb2NiReO6 has been prepared at 6 GPa and temperatures ranging from 1273 to 1373 K. Its crystal structure determined by X-ray powder diffraction and selected area electron diffraction shows monoclinic symmetry with centrosymmetric space group I2/m (a = 5.6021(1) Å, b = 5.6235(1) Å, c = 7.9286(1) Å and β = 90.284°(1)). High angle annular dark field microscopy studies reveal the existence of compositional microdomains. The compound displays a re-entrant spin-glass transition from a ferrimagnetic ordering below T(N) ~ 37 K between the Re(+5) and Ni(+3) (high spin configuration) magnetic sublattices to a spin-glass configuration. Magnetic field dependent magnetization measurements revealed wasp-waisted hysteresis loops at 5 K. These shaped features originate from the antiferromagnetic/ferromagnetic (AFM/FM) competing interactions.

Ferromagnetism and re-entrant spin-glass transition in quasicrystal approximants Au–SM–Gd (SM = Si, Ge)

Magnetic susceptibility and specific heat measurements on quasicrystalline approximants Au–Si–Gd and Au–Ge–Gd reveal that a ferromagnetic (FM) transition occurs at Tc = 22.5(5) K for Au–Si–Gd and at Tc = 13(1) K for Au–Ge–Gd, which are the first examples of ferromagnetism in crystalline approximants. In addition, a re-entrant spin-glass (RSG) transition is observed at TRSG = 3.3 K for Au–Ge–Gd in contrast to Au–Si–Gd. The different behaviors are understood based on the recent structural models reported by Gebresenbut et al (2013 J. Phys.: Condens. Matter 25 135402). The RSG transition in Au–Ge–Gd is attributed to a random occupation of the center of the Gd12 icosahedron by Gd atoms; a central Gd spin hinders the long-range FM order.