Exchange bias, and coercivity investigations in hematite nanoparticles

<abstract> <p>Hematite nanoparticles of average size of 20 nm were synthesized using sol-gel method and the structural characterisations were conducted using XRD and TEM. The XRD profile revealed the coexistence of small fraction of maghemite phase along with the main hematite phase. Magnetization versus applied field (M-H) measurements were performed between −5 and 5 T and respectively in the temperatures 2, 10, 30, 50, 70,100,150,200, and 300 K under zero field and 1, 2, 3, 4 T field cooling. At all field-cooling values, the coercivity was found to display a weak temperatures dependence below 150 K and a strong increase above 150 K reaching the largest value of 3352 Oe at 300 K for the field-cooling value of 3 T. Horizontal and vertical hysteresis loop shifts were observed at all temperatures in both the zero-field and field-cooled states. In the field-cooled state, both loop shifts where found to have significant and nonmonotonic field-cooling dependences. However, because saturation magnetization was not attained in all measurements our calculations were based on the minor hysteresis loops. M-H measurements were performed between −9 and 9 T at room temperature under zero field cooling and 1, 2, 3, 4, 5, 6 T field cooling. Saturation magnetization was not attained, and the loops displayed loop shifts similar to those for the ±5 T sweeping field. The highest coercivity value of 4400 Oe is observed for the 6 T field cooled MH loop. The ferromagnetic (FM) contribution towards the total magnetization was separated from the total magnetization and hysteresis loops displayed both horizontal and vertical shifts. The novel results of the temperature and field dependence of exchange bias were attributed mainly to the magnetic exchange coupling between the different magnetic phases (mainly the FM) and the spin-glass-like regions.</p> </abstract>

Download Full-text

Exchange Bias Properties in Bulk Ni45Co5Mn38Sn12 Heusler Alloy

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.875-877.272 ◽

2014 ◽

Vol 875-877 ◽

pp. 272-276 ◽

Cited By ~ 3

Author(s):

Chao Jing ◽

Ye Jun Yang ◽

Dong Hua Yu ◽

Zhe Li ◽

Xiao Long Wang ◽

...

Keyword(s):

Hysteresis Loop ◽

Exchange Bias ◽

Heusler Alloy ◽

Magnetic Hysteresis ◽

Hysteresis Loops ◽

Bias Field ◽

Magnetic Hysteresis Loop ◽

Zero Field ◽

Co Substitution ◽

Exchange Bias Field

We report the exchange bias properties in the bulk Ni45Co5Mn38Sn12quaternary Heusler alloy. The ferromagnetic (FM) –antiferromagnetic (AFM) interactions get reinforced after the Co substitution for Ni in the Ni-Mn-Sn alloy, which increase the exchange bias field (HE). A maximum shift in hysteresis loops of 306 Oe was observed in the 10 kOe field cooled sample. The origin of this large exchange bias field has been discussed. Magnetic hysteresis loop obtained in the zero field cooled (ZFC) mode shows double-shifted loop, and the reason of this phenomenon has been explained in detail.

Download Full-text

Magnetic and Structural Properties of Barium Hexaferrite Nanoparticles Doped with Titanium

Symmetry ◽

10.3390/sym11060732 ◽

2019 ◽

Vol 11 (6) ◽

pp. 732 ◽

Cited By ~ 1

Author(s):

Abdul Raouf Al Dairy ◽

Lina A. Al-Hmoud ◽

Heba A. Khatatbeh

Keyword(s):

Saturation Magnetization ◽

Permanent Magnets ◽

Sol Gel ◽

Hysteresis Loops ◽

Barium Hexaferrite ◽

Titanium Concentration ◽

Recording Equipment ◽

Auto Combustion ◽

Xrd Patterns ◽

Combustion Technique

Samples of Barium Hexaferrite doped with Titanium BaFe12−xTixO19 with (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized by the sol–gel auto-combustion technique. The powdered samples were divided into two parts, one sintered at 850 °C and another sintered 1000 °C for 1 h and samples were characterized by different experimental techniques. The XRD patterns confirmed the presence of M-type hexaferrite phase. The sizes of the crystallites were calculated by the Scherer equation, and the sizes were in the range of 27–42 nm. Using the hysteresis loops, the saturation magnetization Ms, remanence (Mr), the relative ratio (Mr/Ms), and the coercivity (Hc) were calculated. The study showed that the saturation magnetization (Ms) and remanence (Mr) decreased with increasing titanium concentration and were in the range from 44.65–17.17 emu/g and 23.1–7.7 emu/g, respectively. The coercivity (Hc) ranged between 0.583 and 4.51 (kOe). The magnetic properties of these Barium Hexaferrite doped with Titanium indicated that they could be used in the recording equipment and permanent magnets.

Download Full-text

Iron-Doped Lithium Tantalate Thin Films Deposited by Magnetron Sputtering: A Study of the Iron Role in the Structure and the Derived Magnetic Properties

Crystals ◽

10.3390/cryst10010050 ◽

2020 ◽

Vol 10 (1) ◽

pp. 50 ◽

Cited By ~ 2

Author(s):

Sergio David Villalobos Mendoza ◽

José Trinidad Holguín Momaca ◽

José Trinidad Elizalde Galindo ◽

Diana María Carrillo Flores ◽

Sion Federico Olive Méndez ◽

...

Keyword(s):

Thin Films ◽

Magnetron Sputtering ◽

Magnetic Hysteresis ◽

Hysteresis Loops ◽

Blocking Temperature ◽

Ferromagnetic Behavior ◽

Zero Field ◽

Cooling Curves ◽

X Ray Diffraction ◽

Field Cooling

Fe-doped LiTaO3 thin films with a low and high Fe concentration (labeled as LTO:Fe-LC and LTO:Fe-HC, respectively) were deposited by magnetron sputtering from two home-made targets. The dopant directly influenced the crystalline structure of the LiTaO3 thin films, causing the contraction of the unit cell, which was related to the incorporation of Fe3+ ions into the LiTaO3 structure, which occupied Li positions. This substitution was corroborated by Raman spectroscopy, where the bands associated with Li-O bonds broadened in the spectra of the samples. Magnetic hysteresis loops, zero-field cooling curves, and field cooling curves were obtained in a vibrating sample magnetometer. The LTO:Fe-HC sample demonstrates superparamagnetic behavior with a blocking temperature of 100 K, mainly associated with the appearance of Fe clusters in the thin film. On the other hand, a room temperature ferromagnetic behavior was found in the LTO:Fe-LC layer where saturation magnetization (3.80 kAm−1) and magnetic coercivities were not temperature-dependent. Moreover, the crystallinity and morphology of the samples were evaluated by X-ray diffraction and scanning electron microscopy, respectively.

Download Full-text

Sol-Gel Synthesis and Magnetic, Optical and Impedance Behaviour of Strontium Ferrite Powder

ASME 2011 International Manufacturing Science and Engineering Conference, Volume 2 ◽

10.1115/msec2011-50067 ◽

2011 ◽

Author(s):

Shivendra Kumar Jaiswal ◽

Jitendra Kumar

Keyword(s):

Charge Transfer ◽

Sol Gel ◽

Hysteresis Loops ◽

Lattice Parameter ◽

Space Charge Polarization ◽

Wide Frequency Range ◽

Shell Morphology ◽

Ferrite Powder ◽

Zero Field ◽

Sol Gel Synthesis

An attempt has been made to synthesize SrFeO3-δ powder by sol-gel process involving oxalate formation, its digestion for 4h, drying at 150°C for 24h, and decomposition at 800°C for 10h. The resulting powder is shown to a) exhibit a single phase with a perovskite-type cubic structure and lattice parameter a = 3.862±0.002A˚, b) contain irregular shape particles, and c) display optical absorption peaks corresponding to charge transfer from oxygen to iron (3.73 and 3.41eV), t2g to eg transition of Fe3+ (1.57eV), and crystal field (3d-3d) charge transfer of Fe3+ (1.25eV). Impedance over a wide frequency range of 20Hz-2MHz at 118–318K has contributions from two parallel ‘RC’ circuits belonging to bulk and grain boundaries with the later displaying significant space charge polarization. The relaxation time of polarization follows an Arrhenius behaviour (τ = τo exp[Ea/kBT]) with τo as ∼10−8s and activation energy Ea as ∼50meV. Further, the sample having magnetic character with transition temperature as 853K, coercivity (Hc) = 3748Oe and magnetization 0.09 μB per iron atom (at 17kOe). The zero field cooled and field cooled magnetization versus temperature data in conjunction with constricted hysteresis loops near the origin suggest core-shell morphology for the particles, core being antiferromagnetic with net uncompensated moment and shell conforming to disordered disposition of spins.

Download Full-text

Effects of Na-Doping on Structure and Magnetic Properties of LaCoO3

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.727.403 ◽

2017 ◽

Vol 727 ◽

pp. 403-409

Author(s):

Yi Hao Shen ◽

Qing Rong Yao ◽

Peng Cheng Yang ◽

Jian Qiu Deng ◽

Zong Min Wang

Keyword(s):

Magnetic Properties ◽

Structure Refinement ◽

Hexagonal Phase ◽

Sol Gel ◽

Rhombohedral Structure ◽

Zero Field ◽

Ferromagnetic Transition ◽

Na Doping ◽

Crystallite Sizes ◽

Field Cooling

Effect of Na doping on the structural and magnetic properties of La1-xNaxCoO3 (0≤x≤0.4) nanopowder samples synthesized by sol-gel method have been investigated. Rietveld crystal structure refinement of the X-ray diffraction data shows that La1−xNaxCoO3 (x≤0.3) crystallizes in the rhombohedral structure with space group . The lattice parameters decrease and the crystallite sizes increase with the increase of x. For the sample with x=0.4, a secondary hexagonal phase NaCo2O4 was observed. The zero field cooling (ZFC) and field cooling (FC) curve of the samples (x≤0.3) exhibit a paramagnetic-ferromagnetic transition with decreasing temperature.

Download Full-text

Oscillatory Angular Dependence of Exchange Bias for Epitaxial NiO-Co (001) Bilayers

MRS Proceedings ◽

10.1557/proc-674-t1.6 ◽

2001 ◽

Vol 674 ◽

Cited By ~ 1

Author(s):

S. Dubourg ◽

J.F. Bobo ◽

B. Warot ◽

E. Snoeck ◽

J.C. Ousset

Keyword(s):

Magnetic Field ◽

Exchange Bias ◽

Magnetic Hysteresis ◽

Hysteresis Loops ◽

Field Application ◽

Zero Field ◽

Sign Change ◽

Realistic Description ◽

Sputter Deposited ◽

The Magnetic Field

ABSTRACTWe have sputter-deposited NiO-Co bilayers on MgO (001) substrates. NiO grows epitaxially on MgO at 900°C and subsequently the room deposited 80 Åthick Co films have a fcc crystal structure in epitaxy with the oxide underlayer. These samples were warmed up to 300° C and then zero-field or field cooled through the NiO Néel temperature (a 300 Oe magnetic field was applied along the [100] or the [110] MgO axis). Magnetic hysteresis loops were obtained by magneto-optical Kerr effect, the magnetic field being oriented in the plane of the substrate for various angles α with respect to the [100] direction. The usually expected behavior for such experiments is a smooth angular α dependence of the exchange bias HE close to a cosine with only one sign change over 180°. The high crystallographic coherence of our NiO/Co bilayers induces a very unusual oscillatory HE (α) dependence with several sign changes according to the NiO axis field application. Despite of the Co magnetization switching mechanism which is not a pure coherent rotation, we propose a Stoner-Wohlfhart model including four fold anisotropy and unidirectional exchange anisotropy giving a realistic description of these typical magnetic properties.

Download Full-text

Exchange bias induced after zero-field cooling in antiperovskite compounds Ga1-x NMn3+x

physica status solidi (b) ◽

10.1002/pssb.201451389 ◽

2014 ◽

Vol 252 (3) ◽

pp. 582-588 ◽

Cited By ~ 5

Author(s):

J. C. Lin ◽

P. Tong ◽

D. P. Cui ◽

C. Yang ◽

S. Lin ◽

...

Keyword(s):

Exchange Bias ◽

Zero Field ◽

Zero Field Cooling ◽

Field Cooling

Download Full-text

Co-Ferrite (CoFe2O4): A Material with High Magnetostriction Produced by Sol-Gel Method

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.326.157 ◽

2011 ◽

Vol 326 ◽

pp. 157-164

Author(s):

Nasir Mehmood ◽

Roland Grössinger ◽

Rieko Sato Turtelli ◽

Muhammad Aamir Raza ◽

Sohail Afzal Khan ◽

...

Keyword(s):

Saturation Magnetization ◽

Single Phase ◽

Annealing Temperature ◽

Sol Gel ◽

Hysteresis Loops ◽

Xrd Pattern ◽

Gel Method ◽

Heat Treated ◽

Different Temperatures ◽

Phase Spinel

Polycrystalline Co-ferrite was produced by modified citrate gel method. Samples were afterward heat treated at different temperatures upto 1300°C. The XRD pattern shows that all samples exhibit a single phase spinel structure and improvement and sharpness in intensity of peaks with increasing annealing temperature. Measurement of hysteresis loops demonstrate that after the heat treatment a saturation magnetization of 60- 84 emu/gis obtained. Measurements of the longitudinal magnetostriction gave values between 20 ppm and 130 ppm. Magnetostriction increases gradually with increase in annealing temperature and becomes highest when the saturation magnetization values are larger.

Download Full-text