Spin-glass Behavior Research Articles

Spin Glass State in Strained La2/3Ca1/3MnO3 Thin Films.

Epitaxial strain modifies the physical properties of thin films deposited on single-crystal substrates. In a previous work, we demonstrated that in the case of La2/3Ca1/3MnO3 thin films the strain induced by the substrate can produce the segregation of a non-ferromagnetic layer (NFL) at the top surface of ferromagnetic epitaxial La2/3Ca1/3MnO3 for a critical value of the tetragonality τ, defined as τ = |c − a|a, of τC ≈ 0.024. Although preliminary analysis suggested its antiferromagnetic nature, to date a complete characterization of the magnetic state of such an NFL has not been performed. Here, we present a comprehensive magnetic characterization of the strain-induced segregated NFL. The field-cooled magnetic hysteresis loops exhibit an exchange bias mechanism below T ≈ 80 K, which is well below the Curie temperature of the ferromagnetic La2/3Ca1/3MnO3 layer. The exchange bias and coercive fields decay exponentially with temperature, which is commonly accepted to describe spin-glass (SG) behavior. The signatures of slow dynamics were confirmed by slow spin relaxation over a wide temperature regime. Low-energy muon spectroscopy experiments directly evidence the slowing down of the magnetic moments below ~100 K in the NFL. The experimental results indicate the SG nature of the NFL. This SG state can be understood within the context of the competing ferromagnetic and antiferromagnetic interactions of similar energies.

Anisotropy-induced spin disorder in intergrown, ferrimagnetic Fe7S8 polytypes

The monosulfides of the pyrrhotite omission series (Fe1−xS, 0<x≤0.125) are important remanence carriers for paleomagnetic reconstruction of the Earth's crust and extraterrestrial materials. The ferrimagnetic Fe7S8 polytypes are the endmembers, and their stacking modulations of full and vacant layers generate different magnetic anisotropy properties due to the cation-vacancy configurations. In this study, intergrown long-range ordered polytypes with four- and threefold modulation, i.e., 4C and 3C pyrrhotite, were prepared in a diffusion-driven process by quenching of a natural pyrrhotite crystal with randomized vacancies. In addition, a third constituent with coherence lengths of a few nanometers, denoted 3C*, was found that exhibits spin-glass behavior at about 10 K due to local magnetic anisotropies arising from vacancy-density variations. The concomitant occurrence of this nano-scale constituent with spin disorder and the long-range ordered polytypes indicate competitive diffusion-driven processes during Fe7S8 formation. Such information provides insight into the provenance and genesis of ferrimagnetic pyrrhotite in Earth and extraterrestrial systems and in a broader sense into vacancy-induced materials.

Origin of large magnetocapacitance in K0.5Na0.5NbO3/La0.67Sr0.33MnO3 superlattices

We have investigated magnetocapacitance (MC) performance in superlattices (SLs) of pure ferroelectric and ferromagnetic sublayers for multiferroic applications. ${\mathrm{K}}_{0.5}{\mathrm{Na}}_{0.5}\mathrm{Nb}{\mathrm{O}}_{3}$ (KNN)/${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}$ (LSMO) SLs with LSMO sublayer thicknesses of 5, 7, 9, and 11 unit cell (u.c.) keeping KNN thickness fixed at 6 u.c. were deposited on (001)-oriented $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ substrates alternately for 15 times using pulsed laser deposition (PLD) technique. The crystallinity and layer by layer growth of both constituents were confirmed from X-ray diffraction as well as transmission electron microscopy (TEM). SLs with LSMO layers of 5 and 7 u.c. experience high amount of strain while the in-plane lattice parameter almost matches with the substrate for 9 and 11 u.c. The spin-glass behavior in the SLs below 50 K and the maximum Curie temperature (${T}_{C}$) of $\ensuremath{\sim}206$ K in the thicker film imply the presence of defects as evident by TEM. The defects induced large magnetoresistance (MR) of $\ensuremath{\sim}\ensuremath{-}98%$ was realized at 100 K in the SLs with 9 and 11 u.c. However, the insulating nature in the SLs with 7 and 9 u.c. and insulator to metal transition for 11 u.c. were observed in the transport study. The capacitance as well as magnetocapacitance showed high value at low frequency and reduced monotonically upon increase in the frequency which were well explained by the MR coupled Maxwell-Wagner relaxation model. Finally, the large MC of $\ensuremath{\sim}766$% at standard frequency of 1 kHz with magnetic field of 9 T at 100 K in the SL with optimum LSMO sublayer thickness of 9 u.c. opens a path to design new artificial multiferroics with significant magnetoelectric coupling.

Structure induced quasi-diamagnetism, spin-glass behaviors and exchange bias in crystalline Mn3.5Au0.5N films

Homogeneous Au doped crystalline Mn4N films are grown on MgO (100) substrates by plasma assisted molecular beam epitaxy. Au0 and Mn0 occupy the corner sites in the Mn4N crystal lattice, while Mn1+ atoms are located at face-centered sites, respectively. Mn2p peaks with a shift to the low binding energy side and pronounced spin-glass behaviors as well as exchange bias effects (EB) are presented after the introduction of Au atoms. Mn3.5Au0.5N films exhibit spin-glass behaviors in the temperature range of 15 K to 266 K. Giant exchange bias effects with a 2.16 KOe of positive shift are observed at 100 K in 30 KOe of magnetic field. Spin-glass behaviors disappear at about 266 K and exchange bias effects decrease almost simultaneously to zero at this temperature. We propose that the giant EB in Mn3.5Au0.5N originates from the global interaction between two magnetic sublattices.

Crystal structure, Mössbauer and X-ray photoelectron spectroscopies, and magnetic properties of Sr2FeMo1-xNbxO6 compounds

A systematic experimental study of the crystal structure, Mössbauer and X-ray photoelectron spectroscopies as well as magnetic measurements were carried out to study the effect of Mo substitution by Nb in the Sr2FeMo1-xNbxO6 compounds with x ​= ​0.5, 0.6, 0.7, 0.8 and 1.0. Rietveld analysis made to the crystal structure indicates that the tetragonal structure is preserved for the compounds with a transition phase from I4/m for x ​= ​0.5, 0.6 and 0.7, to an I4/mcm for x ​= ​0.8 and 1.0 by disorder in the Fe and Mo/Nb cations. Mössbauer spectroscopy showed three different environments around iron. XPS results reveal a mixed oxidation states for Mo6+/5+ ions and a trend to Mo5+ as Nb amount increases. XPS valence band measurements indicate a reduction of the charge carries suggesting a more insulating behavior as Nb content increases. This is reflected in magnetic measurements which show a Ms reduction as consequence of Nb content increases, and a non-reversible behavior between ZFC and FC at low temperatures suggest a spin-glass behavior according to previous works.

Quantitative Calculation of the Clustering Behavior of Fe‐Rich and Cr‐Rich REFepCr1−pO3 Crystals

This work has focused on the cluster state of B‐site ions in the rare‐earth perovskite REFepCr1−pO3, and GdFe0.5Cr0.5O3 is taken for instance. This analysis indicates a paramagnetic behavior of the system, which originates from the paramagnetic contribution of the Gd3+. An internal‐field model is used to simplify the superexchange interaction between the A/B‐sites. Furthermore, the cluster state of B‐site ions is computed using the average number of nearest‐neighborhoods. Using Marine Predator Algorithm to fit the experiment data, it is found that Fe–Cr interaction does not conform to the case of ferromagnetic superexchange; therefore, there is no spin glass behavior in this system. Via fitting the Mossbauer spectrum at low temperatures (120 and 12 K), the calculations described above are verified. The calculation gives the hyperfine‐field intervals of 2.47 and 0.92 T at 120 and 12 K. It is found that B‐site ions tend to form clusters. The arrangement of the ions is random and without the tendency of orderly interval occupation of ions (like double perovskite). The study sheds light on the mechanism of single‐ion clustering and introduces new methods for calculating single‐ion clustering states. It can also be applied to the case of other A‐site ions in perovskite system and is not just limited to p = 0.5 in REBpB’1−pO3.

Spin-glass behavior in Li3NiCuBiO6: a two-dimensional distorted honeycomb-lattice

We report a detailed experimental study on the structural and magnetic properties of Li3NiCuBiO6 by means of various characterization techniques. It crystallizes into a monoclinic crystal structure composed of a layered magnetic honeycomb lattice along the c-axis. The existence of glassy state below 4 K is indicated by dc and ac susceptibility measurements. Magnetic contribution to the total heat capacity also peaks around the freezing temperature, and its linear temperature dependence backs our claim of a glassy state in the compound. The calculated magnetic entropy unveils that only ∼26% of the total entropy is released for the system (), and a tremendous amount of spin entropy is still retained in the system. Further, analysis of the frequency-dependent freezing temperature with the help of power law confirms the presence of a spin glass state. Moreover, the appearance of magnetic memory and relaxation effect below freezing temperature manifest the development of the system via a large number of intermediate metastable states. All these measurements confirm the spin-glass behavior of the compound. We consider the presence of different magnetic atoms in honeycomb lattice as the main driving factor for the spin-glass ground state.

High-Pressure Synthesis and Physical Properties of a Spinel Compound FeAl2S4.

A spinel compound FeAl2S4 was successfully synthesized under high-pressure and high-temperature conditions and was systematically characterized via the structural, magnetic, and specific heat measurements. It crystallizes into a cubic structure with the space group Fd3̅m (no. 227) and the lattice constant a = 10.0207(2) Å. A Fe/Al site inversion is found; that is, the molecular formula can be rewritten as (Fe1-xAlx)(Al2-xFex)S4, and the inversion parameter x is about 0.22. Magnetic susceptibility measurements indicate that FeAl2S4 undergoes a spin glass behavior, which is confirmed by ac susceptibility and specific heat measurements. The freezing temperature Tf ∼ 10.5 K and Weiss temperature Tθ ∼ -107.4 K lead to a high frustration parameter f = |Tθ/Tf| of about 10, which suggests that FeAl2S4 is a high-frustration magnet. Our results indicate that high pressure can help stabilize the spinel structure with small R̅σ and the cation inversion plays an important role in the formation of the spin glass state.

Magnetic properties and magnetocaloric effect in RE 55Co30Al10Si5 (RE = Er and Tm) amorphous ribbons

The magnetic and magnetocaloric effects (MCE) of the amorphous RE 55Co30Al10Si5 (RE = Er and Tm) ribbons were systematically investigated in this paper. Compounds with R = Er and Tm undergo a second-order magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) around Curie temperature T C ∼ 9.3 K and 3 K, respectively. For Er55Co30Al10Si5 compound, an obvious magnetic hysteresis and thermal hysteresis were observed at low field below 6 K, possibly due to spin-glass behavior. Under the field change of 0 T–5 T, the maximum values of magnetic entropy change () reach as high as 15.6 J/kg⋅K and 15.7 J/kg⋅K for Er55Co30Al10Si5 and Tm55Co30Al10Si5 compounds, corresponding refrigerant capacity (RC) values are estimated as 303 J/kg and 189 J/kg, respectively. The large MCE makes amorphous RE 55Co30Al10Si5 (RE = Er and Tm) alloys become very attractive magnetic refrigeration materials in the low-temperature region.

Effects of silicon composition on glass formation, crystallization behavior, phase evolution and magnetic properties of the melt-spun Mn-Si-B ribbons

The glass formation, crystallization behavior, phase precipitation, and magnetic properties for a series of melt-spun Mn93−xSixB7 (x = 15, 20, 25, 30) amorphous ribbons were investigated. For x = 15 and 20 amorphous alloys, the crystallization shows one-stage behavior but different precipitated phases. For x = 25 amorphous alloy, a two-stage crystallization behavior occurs, in which the first and second crystallized peaks precipitate the Mn5Si3 and Mn2B, respectively. The broad maximum peak emerges at the temperature-dependent magnetization M(T) curves, indicating the amorphous alloys' spin glass (SG) behavior. Furthermore, the nanocrystalline and amorphous composite structure (NACS) consisting of the single nanocrystalline Mn5Si3 and amorphous phase can be achieved for the amorphous Mn93−xSixB7 alloy with x = 25 by controlling the annealing temperature and duration. The magnetic transitions of the NACS sample significantly differ from the counterpart of its amorphous state. The amorphous alloy undergoes the magnetic phase transition from SG into a paramagnetic state at about 20 K. In comparison, the annealed NACS sample first transforms the SG into a ferromagnetic state at about 15 K and then into a paramagnetic state around 300 K. The difference could attribute to the coupling effect between the nanocrystalline Mn5Si3 with the amorphous phase.

Spin glass and magnetoelectric effect in BiFeO3-Bi0.5K0.5TiO3-Bi0.5Na0.5TiO3 single crystals

We report a cluster spin glass behavior, multiferroicity and magnetoelectric (ME) effects in the single crystals of 0.46BiFeO3-0.54Bi0.5(K0.31Na0.69)0.5TiO3. The crystals are found to possess a pseudo-cubic structure with a weak tetragonal distortion and show ferroelectricity at room temperature with a ferroelectric curie temperature of TC∼630.1 K. The cluster spin glass state in the crystal is evidenced by detailed dc and ac magnetic experiments, including thermo-remnant magnetization, aging effect, memory effect, etc. Magnetodielectric effects, poling enhanced magnetism, and electric field induced acceleration of magnetization relaxation in the spin glass state are observed and ascribed mainly to spin-lattice coupling. These results might suggest an effective route to improve ferromagnetism and ME effects by constructing a spin glass state in BiFeO3-based antiferromagnetic multiferroics.

Top-down and bottom-up approaches to obtain magnetic nanoparticle of Fe3O4 compound: Pulsed laser deposition and chemical route

Our goal in this work was to prepare nanoparticles (NPs) of Fe3O4 using two approaches: top-down and bottom-up. In the former two wavelengths (1064 and 532 nm) were used in the pulsed laser deposition (PLD) technique to produce NPs from α-Fe bulk, with subsequent heat treatment to produce Fe3O4, and in the latter the NPs were produced by chemical co-precipitation route (CR).Transmission Electron Microscopy (TEM) revealed that the as-deposited NPs exhibit a spherical morphology with core/shell structure and with diameters of (8 ± 4) nm (1064 nm) and (16 ± 5) nm (λ = 532 nm) for PLD approach, while for the CR, diameters of 8.0 ± 0.3 and 18.0 ± 0.3 nm were obtained for pure and SiO2-coated samples, respectively. X-Ray diffraction technique with Rietveld method was used to quantify the phases of oxidized NPs, and the percentages obtained were: 58% of Fe3O4 and 42% of α-Fe (532 nm) and 85% of Fe3O4 and 15% of α-Fe (1064 nm). For the samples obtained by CR, no spurious phase was observed in the diffractograms, only a very broad peak of SiO2 was observed around 25°, which indicates that the NPs were coated with SiO2, and this layer is amorphous. From Rietveld refinement, we found that the SiO2-coated sample has the highest Fetet-O-Feoct bond angle, which indicates a greater magnetic coupling between Fe atoms for these samples. Measurements of AC magnetization in different frequencies were carried out for all NPs and a detailed analysis of the dependence of the χ′ peak with T(K) helped to find out the relaxation time of the sample coated with SiO2 is 8.7 × 10−6 s, while for the other samples it was on the order of 10−9 s. Based on the results, it was possible to conclude that the coated sample presents a super spin-glass behavior, while in the other samples a magnetic interaction between NPs and oriented ferromagnetic clusters may be present.

Investigation of the complex magnetic behavior of Ni46.86Co2.91Mn38.17Sn12.06 (at%) magnetic shape memory alloy at low temperatures

The magnetic properties, martensitic transformation characteristics, the magnetic field-induced transformation characteristics, and super spin-glass behaviour at low temperature of Ni46.86Co2.91Mn38.17Sn12.06 (at%) magnetic shape memory alloys (MSMAs) were investigated under various magnetic field levels over temperature intervals from 400 K to 10 K. We observe a small magnetization difference during the martensitic transition evidenced with a visible thermal hysteresis. To investigate the magnetic field induced phase fraction, the minimum magnetic field required to start and complete the magnetostructural phase transition is computed. Super-spin glass features in magnetic data are observed that interacting magnetic clusters are frozen below a critical temperature. Magnetization is computed as a function of temperature at various constant fields using molecular field theory. The critical exponent, β is deduced for the temperature-induced magnetization, which indicates that the MSMA exhibited ferromagnetic ordering during field-cooling and on heating an antiferromagnetic ordering at low temperatures and in low applied magnetic fields. These observations are consistent within the framework of an Ising or Heisenberg model.

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe 2 Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe ₂ Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Investigation of the structural, morphological, and magnetic properties of small crystalline Co–Cu ferrite nanoparticles in the single-domain regime

Single-domain Co0.5Cu0.5Fe2O4 ferrite nanoparticles with a crystallite size of 23 nm were hydrothermally prepared and characterized using x-ray diffraction, transmission electron microscopy, Fourier-transform infrared (FT-IR) spectroscopy, and vibrating sample magnetometry. According to the Rietveld refinement results, the prepared nanoparticles were single-phase with spinel type structures. The transmission electron microscope measurements demonstrated that the nanoparticles were spherical in shape. The FT-IR spectrum showed two principle absorption bands, confirming the characteristic features of cubic spinel ferrites. Magnetization data revealed that the prepared nanoparticles were ferrimagnetic from room temperature to 10 K, with well-defined saturation magnetization, coercivity, and remanence magnetization. The remanence magnetization and coercivity were found to increase with decreasing temperature. The value of room temperature squareness ratio (Mr/Ms) of 0.42 was found to be somewhat similar to that expected (0.5) for a system of noninteracting single-domain nanoparticles, suggesting that the prepared nanoparticles are in a single-domain regime. The temperature dependence of coercivity was found to have slight deviations from Kneller’s law, possibly due to interactions between nanoparticles. The zero field cooled–field cooled curves indicated that below 150 K, the nanoparticles were ferrimagnetic dressed with spin-glass behavior, resulting from interactions between the ferrimagnetic nanoparticles and/or random freezing of surface spins.

Temperature-induced valence-state transition in double perovskite Ba2−xSrxTbIrO6

In this work, a temperature-induced valence-state transition is studied in a narrow composition range of Ba$_{2-x}$Sr$_x$TbIrO$_6$. The valence-state transition involves an electron transfer between Tb and Ir leading to the valence-state change between Tb$^{3+}$/Ir$^{5+}$ and Tb$^{4+}$/Ir$^{4+}$ phases. This first-order transition has a dramatic effect on the lattice, transport properties, and the long-range magnetic order at low temperatures for both Tb and Ir ions. Ir$^{5+}$ ion has an electronic configuration of 5$d^4$ ($J\rm_{eff}$ = 0) which is expected to be nonmagnetic. In contrast, Ir$^{4+}$ ion with a configuration of 5$d^5$($J\rm_{eff}$ = 1/2) favors a long-range magnetic order. For $x$ = 0.1 with Tb$^{3+}$/Ir$^{5+}$ configuration to the lowest temperature (2 K) investigated in this work, a spin-glass behavior is observed around 5 K indicating Ir$^{5+}$ ($J\rm_{eff}$ = 0) ions act as a spacer reducing the magnetic interactions between Tb$^{3+}$ ions. For $x$ = 0.5 with Tb$^{4+}$/Ir$^{4+}$ configuration below the highest temperature 400 K of this work, a long-range antiferromagnetic order at $T\rm_N$ = 40 K is observed highlighting the importance of Ir$^{4+}$ ($J\rm_{eff}$ = 1/2) ions in promoting the long-range magnetic order of both Tb and Ir ions. For 0.2 $\leqslant x \leqslant$ 0.375, a temperature-induced valence-state transition from high-temperature Tb$^{3+}$/Ir$^{5+}$ phase to low-temperature Tb$^{4+}$/Ir$^{4+}$ phase occurs in the temperature range 180 K $\leqslant T \leqslant$ 325 K and the transition temperature increases with $x$. The compositional dependence demonstrates the ability to tune the the valence state for a critical region of $x$ that leads to a concurrent change in magnetism and structure. This tuning ability could be employed with suitable strain in thin films to act as a switch as the magnetism is manipulated.

Experimental and Theoretical Investigations of Fe-Doped Hexagonal MnNiGe.

We report a comprehensive investigation of MnNi0.7Fe0.3Ge Heusler alloy to explore its magnetic, caloric, and electrical transport properties. The alloy undergoes a ferromagnetic transition across TC ∼ 212 K and a weak-antiferromagnetic transition across Tt ∼ 180 K followed by a spin-glass transition below Tf ∼ 51.85 K. A second-order phase transition across TC with mixed short and long-range magnetic interactions is confirmed through the critical exponent study and universal scaling of magnetic entropy and magnetoresistance. A weak first-order phase transition is evident across Tt from magnetization and specific heat data. The frequency dependent cusp in χAC(T) along with the absence of a clear magnetic transition in specific heat C(T) and resistivity ρ(T) establish the spin glass behavior below Tf. Mixed ferromagnetic and antiferromagnetic interactions with dominant ferromagnetic coupling, as revealed by density functional calculations, are experimentally evident from the large positive Weiss temperature, magnetic saturation, and negative magnetic-entropy and magnetoresistance.

Unusual re-entrant spin-glass-behavior and enhanced diamagnetism in sp3-rich sulfur/oxygen doped highly oriented pyrolytic graphite

The recent observations of unusual ferromagnetic and superconductive phenomena in sulfur-doped amorphous carbon and highly oriented pyrolytic graphite (HOPG) have attracted significant attention. In this work we present a novel in-depth investigation on the relationship between magnetic-ordering and sulfur-doping-induced structural modifications in pyrolytic graphite. We demonstrate the nucleation of an unusual amorphous carbon film with sp3-rich characteristics as a result of chemical interactions between sulfur and HOPG. Investigations were performed at the controlled temperatures (T) of ~300, 350, 500 °C, with the residence time parameter varying from 1 min to 15 h. Magnetic characterization revealed a re-entrant spin-glass behavior, possibly originating from vacancy-defects created by sulfur migration. Noticeably, long-time air-exposure of the samples (3 weeks) was found to significantly enhance the diamagnetic component. Density functional theory (DFT) calculations applied to a sp3-rich amorphous‑carbon-system in presence of sulfur-bonding revealed a significant variation of the system-metallicity. We report the presence of insulating states up to sulfur concentrations of ~6.25% (atom %), which then vanish at ~7.5% (atom %) of sulfur-doping. Interestingly, inclusion of the sulfur-migration effect within the DFT calculations revealed significant contributions arising from magnetic-moments generated by electron localization at the vacancy sites. Total spin isosurface analyses (spin up - spin down) highlighted the presence of ferromagnetic contributions arising from carbon-atoms, due to dangling bonds generated by point defects (with the largest magnetic moment values being 0.42 μΒ and 0.379 μΒ respectively).

Spin glass behavior and critical analysis across the magnetic phase transition in Gd2CoMnO6: dc magnetization and ac susceptibility study

We report here on critical analysis across magnetic phase transition and spin dynamics in Gd2CoMnO6. We found that this material behaves differently below and above the applied magnetic field of 20 kOe. The magnetic phase transition switches from nearly mean-field type to unusual class and Tc shifts towards the high temperature above 20 kOe field. The nature of the magnetic phase transition is explored by carrying out critical analysis at low as well as at high magnetic field. The critical exponents obtained at low field using Kouvel-Fisher method are β = 0.65 (2) γ = 0.90 (2), δ = 2.43 and Tc = 120 K. Apparently, these values of critical exponents appear close to mean-field model. For high field the critical exponents are β = 1.24 (2) γ = 0.64 (5), δ = 1.51 (3) and Tc = 128 K. The critical exponents show significant deviation from any universal class. This switchover in the nature of the magnetic phase transition is unique and not seen in many compounds. The formation of non-Griffiths-like clusters in this compound can be a reason for such unique behavior. Further, ac susceptibility has been measured to understand the spin dynamics in detail. The dispersion of frequency-dependent χac below Tc confirms a spin glass state in this material. The observed value of τo and To indicate the slow dynamic spin which is caused by co-existence of Co/Mn spin magnetic moments. The magneto-caloric effect is also presented for Gd2CoMnO6 in this study. The magnetic study and critical analysis across the phase transition reveal a switchover in the nature of phase transition in this material. A non-Griffiths like cluster formation above Tc is found and dynamic susceptibility study reveals a spin glass state below Tc in Gd2CoMnO6.

Thermally-induced co-existence of superparamagnetism and spin-glass like behavior in undoped amorphous AlN thin film

The co-existence of superparamagnetism (SPM) and spin-glass (SG) behavior in undoped amorphous AlN thin film is reported for the first time. The as-deposited AlN film exhibits only SPM behavior while post-deposition annealing at 850 °C for 4 h in a high vacuum of 2 × 10−6 mbar induces SG signature along with SPM. GIXRD measurement confirms the amorphous nature of AlN in as-deposited and annealed films. EDX, RRBS, and XPS measurements indicate the presence of nitrogen vacancies which are drastically enhanced after annealing. The magnetic hysteresis loop for annealed film elucidates the existence of soft and hard magnetic phases attributed to the presence of SPM and SG states, respectively. Temperature-dependent magnetization, magnetization relaxation, and Arrott plot confirm the presence of SG state. Based on the observations and the analysis, the thermally induced enhancement of nitrogen vacancies present in AlN are attributed to be responsible for the co-existence of the SPM and SG state.