scholarly journals Influence of Crystallite Size on the Magnetic Order in Semiconducting ZnCr2Se4 Nanoparticles

Materials ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 3947 ◽  
Author(s):  
Ewa Malicka ◽  
Małgorzata Karolus ◽  
Tadeusz Groń ◽  
Adrian Gudwański ◽  
Andrzej Ślebarski ◽  
...  
Keyword(s):  
Single Crystal ◽  
Specific Heat ◽  
Spin Glass ◽  
Crystallite Size ◽  
Magnetic Order ◽  
Ac Susceptibility ◽  
High Energy ◽  
Zero Field ◽  
Bulk Single Crystal ◽  
Field Cooling

Structural, electrical, magnetic, and specific heat measurements were carried out on ZnCr2Se4 single crystal and on nanocrystals obtained from the milling of this single crystal after 1, 3, and 5 h, whose crystallite sizes were 25.2, 2.5, and 2 nm, respectively. For this purpose, the high-energy ball-milling method was used. The above studies showed that all samples have a spinel structure, and are p-type semiconductors with less milling time and n-type with a higher one. In turn, the decrease in crystallite size caused a change in the magnetic order, from antiferromagnetic for bulk material and nanocrystals after 1 and 3 h of milling to spin-glass with the freezing temperature Tf = 20 K for the sample after 5 h of milling. The spin-glass behavior for this sample was derived from a broad peak of dc magnetic susceptibility, a splitting of the zero-field-cooling and field-cooling susceptibilities, and from the shift of Tf towards the higher frequency of the ac susceptibility curves. A spectacular result for this sample is also the lack of a peak on the specific heat curve, suggesting a disappearance of the structural transition that is observed for the bulk single crystal.

NOVEL BINARY SPIN GLASS ALLOYS SYNTHESIZED BY MECHANICAL MILLING

1995 ◽  
Vol 09 (03n04) ◽  
pp. 145-162 ◽  
Author(s):  
G. F. ZHOU ◽  
H. BAKKER
Keyword(s):  
Spin Glass ◽  
Mechanical Milling ◽  
Spin Glasses ◽  
Ac Susceptibility ◽  
Freezing Temperature ◽  
High Energy ◽  
Zero Field ◽  
High Concentration ◽  
Freezing Temperatures ◽  
Field Cooling

A few novel binary spin glass alloys have been successfully synthesized by mechanical milling of ordered intermetallic compounds in a high energy ball mill. These alloys are amorphous Co 2 Ge , atomically disordered crystalline GdAl 2, and ball-milled crystalline and amorphous CoZr. The characteristic features of spin glasses are observed; these are (a) the sharp cusps at the freezing temperature T f in both ac and dc magnetic susceptibility versus temperature curves and their peculiar sensitivity to the external magnetic field; (b) the irreversibility, i.e. the difference in value and shape between the magnetisation versus temperature curves after zero field cooling (ZFC) and field cooling (FC) at temperatures below T f and (c) the displacement of the FC magnetisation curve relative to ZFC curve and the corresponding remanence in the FC curve at low temperatures. The freezing temperatures are 41, 65, 35, and 11 K, respectively, which are defined by the sharp cusps in the lowest field ac susceptibility versus temperature curves. The freezing temperatures are lowered with increasing external field. The common feature of these materials is that all are binary alloys with a rather high concentration of the magnetic component. The discovery of these novel spin glasses is of significance because they not only represent new classes of spin glass materials but also demonstrate the use of mechanical milling as a novel technique to synthesize various new materials such as spin glasses. The results are reviewed briefly.

Spin-Glass Behavior and the Magnetic Relaxation Effects in Nd0.90Sr0.10CoO3

2012 ◽  
Vol 557-559 ◽  
pp. 680-683
Author(s):  
Yi Yun Yang
Keyword(s):  
Low Temperature ◽  
Spin Glass ◽  
Mirror Symmetry ◽  
Magnetic Relaxation ◽  
Ac Susceptibility ◽  
Experimental Studies ◽  
Polycrystalline Sample ◽  
Zero Field ◽  
Relaxation Effects ◽  
Field Cooling

The magnetization, ac susceptibility and magnetic relaxation of Nd0.90Sr0.10CoO3polycrystalline sample were systematically investigated in this paper. The experimental studies of susceptibility and magnetic relaxation evidence the existence of a low-temperature spin-glass. A dynamic analysis of ac susceptibility implies a spin-glass transition temperature TSG =12.17 K and the dynamical exponent zv=8. Moreover, low-temperature zero-field cooling and field cooling magnetic relaxation show perfectly mirror symmetry, and field cooling processes relaxation obeys a stretched exponential form. Therefore, our study confirms that the phase separation in Nd0.90Sr0.10CoO3originates from both the ferromagnetic clusters interaction and the spin glasslike phase at low temperature.

Surface Spin-glass Freezing and Blocking in NiFe2O4 Nanoparticles

2010 ◽  
Vol 1256 ◽  
Author(s):  
Kashif Nadeem ◽  
Heinz Krenn
Keyword(s):  
Low Temperature ◽  
Spin Glass ◽  
Ac Susceptibility ◽  
Sol Gel ◽  
Ferrite Nanoparticles ◽  
Core Shell ◽  
Temperature Hysteresis ◽  
Zero Field ◽  
Temperature Peak ◽  
Surface Spin

AbstractWe prepared single-phase nickel ferrite nanoparticles separated by silicon dioxide using sol-gel method with tetraethyl orthosilicate (TEOS) as a precursor for SiO2. The magnetic properties are investigated by using SQUID-magnetometry over a broad temperature range (4.2 – 350 K), magnetic field (2–70,000 Oe) and frequency (0.1 – 1000 Hz) range. The particle size is in the range 8 – 12 nm. Exchange bias and spin disorder appear at the core-shell interface due to broken bonds on the surface. Disorder and core-shell interaction induces spin-glass freezing which is manifested by a low temperature peak in the AC susceptibility well separated from magnetic blocking peak. This low temperature peak is assigned to spin-glass freezing. The proof of spin-glass freezing is managed by zero field cooled/field cooled (ZFC/FC), frequency and DC field dependence of AC susceptibility, low temperature hysteresis loop and time dependent thermoremanent magnetization at different temperatures. All the measurements stated above signify blocking/unblocking at higher temperatures and surface spin-glass freezing at low temperatures. The aim of our work is to contribute to a better understanding of “spin-frozen” magnetic ferrite nanoparticles at diameters 8 – 12 nm which could be important in future for stabilizing the magnetic state of “core-shell”-structured nanomagnets.

scholarly journals Effect of pH on Structural, Magnetic and FMR Properties of Hydrothermally Prepared Nano Ni Ferrite

2017 ◽  
Vol 15 (1) ◽  
pp. 53-60 ◽  
Author(s):  
Sadeq H. Lafta
Keyword(s):  
Crystallite Size ◽  
Lattice Constant ◽  
Spinel Ferrite ◽  
Resonance Field ◽  
Zero Field ◽  
Metal Chlorides ◽  
Nano Nickel ◽  
G Value ◽  
Zero Field Cooling ◽  
Field Cooling

AbstractNano nickel ferrite particles were prepared at pH values 1.5, 4, 7, 10, 13 by a hydrothermal method using metal chlorides and NaOH as an oxidant and solution basicity controller. There is a phase transition from hematite to spinel ferrite that begins when the pH reaches 4. The lowest crystallite size (4 nm) was associated with a highest lattice constant (8.345 Å), at pH=4. Whereas maximum crystallite size 64.5 nm corresponds lattice constant of 8.298 Å at pH=10. The highest magnetization (48 emu/g) value was achieved for the sample prepared at pH=7, which at the same time has a lower coercivity. The samples synthesized at pH ≥4 show superparamagnetic behavior owing to its low particle size and to zero field cooling and field cooling measurements. The ferromagnetic resonance (FMR) cavity tests analysis show that the broadened linewidth (770 Oe) and high imaginary permeability or high microwave absorption which is linked to high magnetization and low coercivity of superparamagnetic particles and their aggregation. There was a shift in the resonance field due to internal fields and cation distribution.

scholarly journals Spontaneous Zero-Field Cooling Exchange Bias in Ni–Co–Mn–Sn Metamagnetic Heusler Sputtered Film

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2188
Author(s):  
Vasileios Alexandrakis ◽  
Iván Rodríguez-Aseguinolaza ◽  
Dimitrios Anastasakos-Paraskevopoulos ◽  
Jose Manuel Barandiarán ◽  
Volodymyr Chernenko ◽  
...  
Keyword(s):  
Exchange Bias ◽  
Ac Susceptibility ◽  
Heusler Alloys ◽  
Exchange Interactions ◽  
Careful Study ◽  
Zero Field ◽  
Magnetic Clusters ◽  
Magnetocaloric Materials ◽  
Zero Field Cooling ◽  
Field Cooling

Metamagnetic off-stoichiometric Heusler alloys are actively being investigated because of their great potential as magnetocaloric materials. These properties are intimately related to the nanoscale homogeneity of their magnetic properties, mainly due to a strong influence of the nature of the exchange interactions between Mn atoms on the magnetism of the alloys. In this work, a spontaneous exchange bias phenomenon on a Ni–Co–Mn–Sn metamagnetic Heusler sputtered film is presented and studied in detail. More particularly, a series of DC magnetization curves measured as a function of the temperature demonstrates that the system exhibits canonical spin glass-like features. After a careful study of the field-cooling and zero-field-cooling curves measured on this system, the existence of magnetic inhomogeneities is inferred, as a consequence of the competition between ferromagnetic and antiferromagnetic exchange interactions between Mn atoms. Further AC susceptibility measurements on this system demonstrate that the underlying exchange bias phenomenon can be attributed to a magnetic clusters model based on superferromagnetic-like interactions present in the film. These findings suggest that the spontaneous exchange bias exhibited by the studied system is a consequence of the formation of this superferromagnetic-like state.

Photoluminescence and Raman Spectra of Flux Processed Bulk Single Crystal GaN

2001 ◽  
Vol 680 ◽  
Author(s):  
Chae Ryong Cho ◽  
Sang Eon Park ◽  
Yong Chan Cho ◽  
Se-Young Jeong
Keyword(s):  
Single Crystal ◽  
Photoelectron Spectroscopy ◽  
High Energy ◽  
Bulk Single Crystal ◽  
X Ray Diffraction ◽  
Phonon Modes ◽  
X Ray ◽  
Growth Method ◽  
Bulk Single Crystals ◽  
Gan Crystal

ABSTRACTBulk wurtzite-GaN crystal was obtained with a size more than 3 mm along the length of the crystal and with a thickness 200 ∼ 300 µm at around 750°C and 100 bar for 24 hrs in the flux growth method. The structural and compositional property of the GaN bulk single crystal was also studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Photoluminescence, cathodoluminescence and micro-Raman measurements at room temperature are investigated for bulk single crystals of wurtzite GaN. The cathodoluminescence peak of near band-to-band transition at 365.5 nm and the E2(high energy, 568 cm−1) and A1(LO, 737 cm−1) Raman phonon modes were obtained according to the different position of the (0001) surface of GaN grown by flux method. Sharp line shape for the strain-sensitive E2 (high) mode is considered to be due to the high crystalline quality of the crystal.

scholarly journals Observation of Spin-Glass Behavior in Spinel Compound CoGa2O4

2021 ◽  
Author(s):  
Jiyu Hu ◽  
Yongqing Ma ◽  
Xucai Kan ◽  
Chaocheng Liu
Keyword(s):  
Spin Glass ◽  
Ac Susceptibility ◽  
Freezing Temperature ◽  
Peak Shift ◽  
Synthesis Process ◽  
Zero Field ◽  
Magnetic Frustration ◽  
Dynamical Exponent ◽  
Spin Glass Behavior ◽  
Fitting Parameters

Abstract In this work, the synthesis process, crystal-structure, and comprehensive physical properties of spinel compound CoGa2O4 have been investigated. The competition between antiferromagnetism (AFM) and ferromagnetism (FM) are considered to be the crucial elements for resulting in spin-glass (SG) behavior due to magnetic frustration. The observed SG behavior is determined by the temperature dependence of magnetization M(T) curves under the ZFC (zero-field-cooled) and FCC (field-cooled) processes, where form the intense irreversibility divergence. Moreover, the corresponding fitting parameters (the freezing temperature T0 = 9.32 K, the flipping time τ0 = 4.49 × 10-10 s, and the dynamical exponent zν = 4.46) strongly indicate the existence of the SG behavior. Meanwhile, as another specific characteristic for SG, in our present work, frequency (f) and magnetic field (H) have a strong influence on the peaks of AC susceptibility. From where, with the increase of f and H, the freezing temperature follows a corresponding peak shift. All the above phenomena and relevant analyses of magnetic frustration behavior confirm the typical SG behavior in CoGa2O4 system.

scholarly journals Magnetic Attributes of NiFe2O4 Nanoparticles: Influence of Dysprosium Ions (Dy3+) Substitution

Nanomaterials ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 820 ◽  
Author(s):  
Munirah Abdullah Almessiere ◽  
Y. Slimani ◽  
H. Güngüneş ◽  
S. Ali ◽  
A. Manikandan ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Spin Glass ◽  
Ac Susceptibility ◽  
Freezing Temperature ◽  
Magnetic Interactions ◽  
Blocking Temperature ◽  
Zero Field ◽  
X Ray Diffraction ◽  
Slowing Down ◽  
Transmission Electron

This paper reports the influence of dysprosium ion (Dy3+) substitution on the structural and magnetic properties of NiDyxFe2−xO4 (0.0 ≤ x ≤ 0.1) nanoparticles (NPs) prepared using a hydrothermal method. The structure and morphology of the as-synthesized NPs were characterized via X-ray diffraction (XRD), scanning and transmission electron microscope (SEM, and TEM) analyses. 57Fe Mössbauer spectra were recorded to determine the Dy3+ content dependent variation in the line width, isomer shift, quadrupole splitting, and hyperfine magnetic fields. Furthermore, the magnetic properties of the prepared NPs were also investigated by zero-field cooled (ZFC) and field cooled (FC) magnetizations and AC susceptibility measurements. The MZFC (T) results showed a blocking temperature (TB). Below TB, the products behave as ferromagnetic (FM) and act superparamagnetic (SPM) above TB. The MFC (T) curves indicated the existence of super-spin glass (SSG) behavior below Ts (spin-glass freezing temperature). The AC susceptibility measurements confirmed the existence of the two transition temperatures (i.e., TB and Ts). Numerous models, e.g., Neel–Arrhenius (N–A), Vogel–Fulcher (V–F), and critical slowing down (CSD), were used to investigate the dynamics of the systems. It was found that the Dy substitution enhanced the magnetic interactions.

A MONTE CARLO STUDY OF THE SPECIFIC HEAT OF DILUTED ANTIFERROMAGNETS

1999 ◽  
Vol 10 (01) ◽  
pp. 233-239
Author(s):  
M. STAATS ◽  
K. D. USADEL
Keyword(s):  
Phase Transition ◽  
Specific Heat ◽  
Three Dimensional ◽  
Monte Carlo Study ◽  
Paramagnetic State ◽  
Zero Field ◽  
Longe Range ◽  
Zero Field Cooling ◽  
Ordered State ◽  
Field Cooling

The three-dimensional diluted antiferromagnet in a magnetic field has a longe-range ordered state for sufficiently low temperatures and external fields. We study the irreversibilities at the phase transition from this state into the paramagnetic state at higher temperatures. Performing field cooling and zero field cooling simulation procedures we find a small irreversibility in the internal energy and the specific heat, although the behavior of the order parameter is irreversible and the phase transition is suppressed in the FC case. The specific heat shows a noncritical broad maximum above the transition temperature Tc. The results are compatible with recent experimental results obtained by Satooka et al., whereas our interpretation of the data is different.

Experiments on REM and SREM using a Tem/Stem Microscope with a Configurable Angle-Resolving Detector

1990 ◽  
Vol 48 (1) ◽  
pp. 338-339
Author(s):  
H. Banzhof ◽  
I. Daberkow
Keyword(s):  
Electron Microscopy ◽  
Single Crystal ◽  
Crystal Surface ◽  
High Energy ◽  
Contrast Effects ◽  
Atomic Steps ◽  
Single Crystal Surfaces ◽  
Platinum Single Crystal ◽  
Reflection Electron Microscopy ◽  
Beam Reflection

A Philips EM 420 electron microscope equipped with a field emission gun and an external STEM unit was used to compare images of single crystal surfaces taken by conventional reflection electron microscopy (REM) and scanning reflection electron microscopy (SREM). In addition an angle-resolving detector system developed by Daberkow and Herrmann was used to record SREM images with the detector shape adjusted to different details of the convergent beam reflection high energy electron diffraction (CBRHEED) pattern.Platinum single crystal spheres with smooth facets, prepared by melting a thin Pt wire in an oxyhydrogen flame, served as objects. Fig. 1 gives a conventional REM image of a (111)Pt single crystal surface, while Fig. 2 shows a SREM record of the same area. Both images were taken with the (555) reflection near the azimuth. A comparison shows that the contrast effects of atomic steps are similar for both techniques, although the depth of focus of the SREM image is reduced as a result of the large illuminating aperture. But differences are observed at the lengthened images of small depressions and protrusions formed by atomic steps, which give a symmetrical contrast profile in the REM image, while an asymmetric black-white contrast is observed in the SREM micrograph. Furthermore the irregular structures which may be seen in the middle of Fig. 2 are not visible in the REM image, although it was taken after the SREM record.

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