Value Of Exchange Bias Field Research Articles

Structural tuning interlinking various optical, dielectric and magnetic trends in annealed Mn0.5Zn0.5Fe2O4 spinel ferrites nanostructures

Mn0.5Zn0.5Fe2O4 nanoparticles have been synthesized through co-precipitation technique and annealed up to 700 °C. The values of crystallite size and lattice constant ranges from 11 to 21 nm and 8.4550 to 8.4732 Å respectively for most prominent peak (3 1 1) with a switching at 400 °C. X-ray density ranges from 5.18 to 5.25 g/cm3, lattice strain decreases with the increase of annealing temperature and ranges from (10.39–5.55) × 10-3 which in turn affects the line defects to decrease with annealing temperature (8.18–2.33) × 1015 lines/m2. The high values of specific surface area emphasize on energy storage applications like in supercapacitor. Magnetic properties including magnetic moment (nB = 0.0967–3.441 μB), saturation magnetization (Ms = 2.2906–81.4769 emu/g), coercivity (Hc = 24.80–109.35 Oe), anisotropic field (Hk = 49.00–198.38 Oe) and magneto-crystalline anisotropy (K1 = 87.22–4570.59 erg/g) manifested overall improved magnetic trends. The value of exchange bias field has been observed up to 108.18 Oe. The higher values of band-gaps (2.45–2.62 eV and 2.22–2.46 eV) lead to prospective solar cell applications. The range of metallization criterion [0.49–0.42] along with high refractive index values (3–9.6) suggest that synthesized nanomaterial could be utilized for the new generation of nonlinear optical materials and hetero-laser applications. Nyquist/Cole-Cole plots confirm the non-Debye type relaxation process and their shape leads to the existence of multiple electrical responses in the prepared samples.4.

Observation of large exchange bias above room temperature in antiferromagnetic hexagonal Mn3Ga

We report the observation of large exchange bias effect in hexagonal Mn3Ga melt-spun ribbons with triangular antiferromagnetic order. The observation shows that the maximum field cooling exchange bias field can reach 3.3 kOe, and the large value of exchange bias field can persist above room temperature until 385 K (blocking temperature). Meanwhile, the zero-field cooling exchange bias field can also reach the considerable value around 0.25 kOe–0.4 kOe. The training effect result conforms well to the typical exchange bias effect. After annealing the ribbons sample, the ordered sample does not show the exchange bias any more, which relates to the atoms ordering in Mn3Ga ribbons.

Size-dependence of the exchange bias effect observed in [formula omitted] (x = 0.05 and 0.20) compounds

The particle-size effects on the exchange bias phenomenon have been investigated in perovskite Nd1-xDyxCrO3 (x = 0.05 and 0.20) compounds, which are obtained via co-precipitation method. The analysis of the X-ray diffraction data through Rietveld refinement show that, independently of calcination temperatures and nominal compositions, samples exhibit a single phase with orthorhombic structure and Pnma space group. The calculated particle average diameters via Scherrer formula range from 50 to 90 nm. The magnetic-field and T-dependencies of magnetization using the field-cooled-cooling protocol are performed. For all samples, the MvsT curves present a first magnetic transition at T ≈ 210 K likely associated with the antiferromagnetic order of Cr3+ ions and a second one at T ≈ 40 K assigned to their spin reorientation. Magnetic hysteresis loops show the presence of a negative exchange bias phenomenon for all samples, whose values of exchange bias field, HEB, decrease with increasing particle size. We argue that this behavior is mainly associated to the uncompensated surface spins, which are dependent on the particle size.

Higher ferromagnetic resonance frequency in NiFe/FeMn film obtained by flash annealing in reversing field

The unsaturated magnetization reversal by pulsed current annealing was investigated in exchange biased NiFe(15 nm)/FeMn(10 nm) bilayer. The magnetization reversal was conducted by energizing and thus heating the film under an external applied magnetic field ( $$H_{\text{a}}$$ ) with the direction opposite to the deposition field ( $$H_{\text{d}}$$ ). The static and dynamic magnetic properties of the films before and after rapid annealing were characterized using vibrating sample magnetometer, anisotropic magnetoresistance (AMR) and vector network analyzer measurements. When the samples were annealed at 40 and 45 V condenser voltages, greater values of rotational anisotropy $$(H_{\text{rot}} )$$ , ferromagnetic resonance frequency ( $$f_{\text{r}}$$ ) and smaller values of exchange bias field $$(H_{\text{e}} )$$ , exchange bias field in AMR measurement ( $$H_{\text{e}}^{\text{MR}}$$ ), and magnetoresistance in the samples were obtained, which is attributed to the unsaturated reversed magnetization in reversing magnetic field. A suggested model for which the scattered magnetization of magnetic moment results in additional unstable antiferromagnetic spins in the film was proposed to explain this interesting phenomenon.

Coexisting exchange bias effect and ferroelectricity in geometrically frustrated ZnCr2O4

Concomitant occurrence of exchange bias effect and ferroelectric order is revealed in antiferromagnetic spinel ZnCr2O4. The exchange bias effect is observed below antiferromagnetic Neél temperature (TN) with a reasonable value of exchange bias field ( Oe at 2 K). Intriguingly, the ratio is found unusually high as ∼2.2, where HC is the coercivity. This indicates that large HC is not always primary for obtaining large exchange bias effect. Ferroelectric order is observed at TN, where non-centrosymmetric magnetic structure with space group associated with the magnetoelectric coupling correlates the ferroelectric order, proposing that, ZnCr2O4 is an improper multiferroic material. Rare occurrence of exchange bias effect and ferroelectric order in ZnCr2O4 attracts the community for fundamental interest and draws special attention in designing new materials for possible electric field control of exchange bias effect.

Structural and magnetic properties of NiCr1.9Mn0.1O4

Polycrystalline NiCr1.9Mn0.1O4 within nanoscale has been synthesized by sol–gel method. X-ray diffraction results prove pure formation of the sample without any other impurities. Characterizations of scanning electron microscopy and X-ray fluorescence reveal the good crystallinity and desired element ratio of the phase. Magnetic hysteresis loop measured at 10 K after cooling the sample in applied field of 30 kOe shows asymmetry both in the field and magnetization axes with a bias field about 3316.5 Oe and a magnetization shift about 0.381 emu/g. This exchange bias (EB) behavior has also been studied as the function of measuring temperature and applied cooling field. The values of EB field and magnetization shift are found to depend strongly on temperature as well as the cooling field. The accompanying training effect is also observed in the sample. Irreversibility in temperature dependence of magnetization at different applied fields indicates the presence of spin-glass-like (SGL) phase. High field relaxation measurement confirms the existence of SGL state. The results suggest that different formation of ferromagnetic and antiferromagnetic sublattice orders with spin frustration due to the doping of Mn cations in the sample leads to these interesting magnetic properties.

Elliptic NdCrO3 microplate by a simple one‐step hydrothermal synthesis route and its characterization and magnetic properties

Elliptic NdCrO3 microplates were synthesized by a simple and facile one‐step hydrothermal method of processing temperature 280 °C for 3 days. The products prepared in this paper have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), X‐ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR) and field‐emission scanning electron microscopy (FESEM). The magnetic properties of the final sample are also studied. The XRD pattern indicates the pure orthorhombic phase for NdCrO3 particles, the XPS, XRF and FTIR results further demonstrate the composition and purity of the final product. A possible growth mechanism for elliptic NdCrO3 microplates is proposed. Through the investigation of magnetic properties, it can be generally concluded that the orthorhombic elliptic NdCrO3 microplates exhibit typical behaviors of magnetic transition, spin reorientation transition and magnetic exchange bias. The Néel temperature is 218 K and the spin reorientation transition temperature is 46 K. The hysteresis loop under 5 K shows that the value of exchange bias field (Hex) is 12 Oe and the shift of remanent magnetization (ΔM) is 0.008 emu/g, respectively.

Magnetocaloric properties, exchange bias, and critical behavior of Ge substituted Ni50Mn36Sn14 Heusler alloys

The effect of Ge substitution on the magnetic, magnetocaloric, and exchange bias properties of Heusler alloy system Ni50Mn36Sn14-xGex (x = 1, 2) has been investigated. With the increase of Ge content, the cell volume decreases due to the smaller Ge radius and the martensitic transition temperature increases, while the Curie temperature of the austenite phase shows a small decrease. Metamagnetic behavior is observed in the low temperature magnetization isotherms for x = 1, whereas it is less pronounced in x = 2. The maximum magnetic entropy changes associated with the martensitic transition are 7.8 J/kg K and 2.3 J/kg K for x = 1 and 2, respectively, for a field change of 5 T. Relative cooling power is found to be more in the vicinity of the Curie temperature of the austenite phase, compared to that at the martensitic transition temperature in both x = 1 and 2. At low temperatures, both the samples exhibit exchange bias effect, with x = 2 showing higher value of exchange bias field. This is ascribed to the coexistence of ferromagnetic and antiferromagnetic interactions in these alloys. Further, the critical behavior of the austenite phase of both the alloys is studied and the values of the critical exponents are found to be different from the mean field values, which is attributed to the magnetic inhomogeneity originated due to Ge substitution.

Bipolar switching of magnetization and tunable exchange bias in NdCr1−xMnxO3 (x = 0.0–0.30)

Polycrystalline samples of NdCr1−xMnxO3 (x = 0.0–0.30) were prepared by sol-gel method. Samples in the composition range, x = 0.10 to 0.20, exhibit magnetization reversal, and the magnetization compensation temperature (Tcomp) is found to increase from 110 K to 157 K with increase in Mn concentration. The magnetization reversal behavior is explained by considering paramagnetic moments of Nd3+ and Mn3+ ions under the influence of negative internal magnetic field and the canted ferromagnetic component of Cr3+ ions. Bipolar switching of magnetization by varying either the applied field H = 200 Oe to 3000 Oe or temperature through Tcomp is shown. Tunable exchange bias behavior was observed for x = 0.10 to 0.20 samples, and the value of exchange bias field, HEB, could be tuned from −1.6 kOe to +0.39 kOe for x = 0.10 sample. The origin of exchange bias is explained by considering the antiferromagnetic interaction between ferromagnetic component of Cr3+ ions and the paramagnetic components of Nd3+ and Mn3+ ions. The x = 0.30 sample exhibits ferromagnetic like behavior due to super exchange interaction in Cr3+–O2−–Mn3+ networks.

Exchange bias effect in Ti doped nanocrystalline SrFeO3-δ

Materials of Ti doped nanocrystalline SrFeO3-δ were synthesized through solid state reaction. Detailed magnetization measurements were carried out in zero field cooled (ZFC) and field cooled (FC) conditions. Compounds of SrFe1-xTixO3-δ (x = 0.1 to 0.3) are found to be spin glass and parent compound is a helical antiferromagnet. Non magnetic Ti4+ reduces the strength of exchange interactions and the curvature of hysteresis is changed towards concave nature. Exchange bias is observed below the peak temperature (irreversibility in magnetization (TIrr)) in ZFC-FC of SrFe1-xTixO3-δ (x = 0 to 0.3). The coercivity and exchange bias field values are found to be decreases with increase in temperature. Observed exchange bias effect is attributed to competition between antiferromagnetic superexchange and ferromagnetic double exchange interactions.

Size-dependent exchange bias in ferromagnetic (core)/antiferromagnetic (shell) nanoparticles

We report a numerical study of the dependence of exchange bias on ferromagnetic core/antiferromagnetic shell dimension in an isolated nanoparticle, on the basis of a modified Metropolis Monte Carlo simulation. A pronounced exchange bias field is obtained at a finite size of ferromagnetic core radius, while the value of exchange bias field decreases monotonously up to a lower stable value with further increasing core sizes. Due to the complex core/shell structure and the mode conversion of magnetization reversal for various core sizes, the dependence of exchange bias field on the ferromagnetic component size is different from that in planar systems. Moreover the exchange bias field can be stabilized above a certain antiferromagnetic shell thickness, where the effective anisotropy of the whole antiferromagnetic shell becomes strong enough. It has been demonstrated unambiguously how the core and shell dimensions optimize the exchange bias.

Magnetic Properties of La0.8K0.2MnO3Nanoparticles

Magnetic properties of La 0.8 K 0.2 MnO 3 have been studied on nanoparticles prepared by glycine – nitrate method. As prepared nanoparticles and samples annealed at 300°C/2 hours adopt orthorhombic crystal structure (space group Pbnm ). Crystal structure and particles size were modified by heat treatment. The exchange bias effect was observed on samples with particles size smaller than 50 nm.Cooling in magnetic field H cf ≠ 0 through the Curie temperature T C shifts hysteresis loop in horizontal and vertical direction. The values of exchange bias field H E , coercive field H c , remnant asymmetry μ E and coercive magnetization μ c increase with increasing value of cooling field H cf . In addition the training effect was studied. Basic magnetic properties like the Curie temperature T C and the saturated magnetization μ s increase and H E or μ E decrease with heat treatment. Heat treatment at 600 °C/2 hours increases the average size of nanoparticles to about 60 nm, crystal structure changes to rhombohedral structure (space group R c ) and EB effect vanishes.

Sign reversal of magnetization and exchange bias field in LaCr0.85Mn0.15O3

The sign reversal of magnetization is observed in LaCr0.85Mn0.15O3 compound and the maximum magnetic compensation temperature (Tcomp) was at around 100 K. We have also observed negative and positive values of exchange bias field (HEB) having sign reversal at around Tcomp. The value of HEB could be tuned from −2.1 kOe to + 2.6 kOe with change in temperature. The competition between the magnetic moment due to the canted ferromagnetic component of Cr3+ ions and the paramagnetic component of doped Mn3+ ions under the negative internal field gives rise to magnetization reversal. The origin of sign reversal of HEB is discussed in detail.

Microstructure, martensitic transitions, magnetocaloric, and exchange bias properties in Fe-doped Ni-Mn-Sn melt-spun ribbons

The effects of Fe substitution for Ni on microstructure, phase transformations, magnetocaloric effect, and exchange-bias behavior of the Ni46−xFexMn43Sn11 (x = 0–3) alloy ribbons have been investigated. The free surface of as-spun Fe-doped ribbons shows the granular microstructure containing multiple shapes (the tree leaf-like, small columnar grain, etc.), while the ordered columnar grains are observed in fracture cross-section. The martensitic structural transition temperature (TM) of as-annealed ribbons decreases from 240 K for x = 0 to 185 K for x = 3 due to the decrease in valence electron concentration, while the Curie temperature of the austenitic phase remains almost unchanged (TC = 275 K). The positive values of magnetic entropy changes (+ΔSM), around TM, are 21.0, 29.1, 24.1, and 14.8 J/kg K for x = 0–3, respectively, while the negative −ΔSM values vary in 3.0–3.5 J/kg K range around TC, under a field change of 0–5 T. The values of exchange-bias field (HE) at 10 K change in the range of 469 to 534 Oe and the coercivity (HC) slightly decreases from 245 to 186 Oe, respectively, as x is increased.

The phase evolution, magnetic and exchange bias properties in Fe50Mn24+xGa26−x (x = 0–3) melt-spun ribbons

Effect of Ga content on the phase constitution, magnetic phase transition temperatures (TC), and exchange bias (EB) behaviors of Fe50Mn24+xGa26−x (x=0, 0.5, 1, 3) as-spun ribbons have been investigated. Fe50Mn24Ga26 ribbon exhibits a magnetic phase transition of B2-type structure from FM to PM state at TC1=190K. Another magnetic phase transition of face-center-cubic structure from AFM to FM takes place at TC2=240K for Fe50Mn25Ga25 sample. The values of exchange bias field (HE) at 10K after field-cooling (FC) at 30kOe from 300K are 14, 41, 1886, 1740Oe, respectively, as x is increased from 0 to 3. The phenomena are attributed to the change of exchange interactions at FM/AFM interfaces due to the change of proportion of FM and AFM phases in low temperature magnetic states. The maximum exchange bias field HE=2.4kOe at 10K after field-cooling at 40kOe is observed for Fe50Mn25Ga25.

The Effect of B Doping on the Martensitic Transitions, Magnetocaloric and Magnetic Properties in Ni$_{48}$Mn$_{39}$In$_{13-{\rm x}}$B$_{\rm x}$ Ribbons

The influence of boron substitution for indium on phase transformation, magnetocaloric and exchange bias (EB) properties in annealed Ni48Mn39In13-xBx (x = 1-4) ribbons has been investigated. It is observed that an increase in B concentration strongly affects the magnetic state of the martensitic phase, the magnetic entropy change and the EB properties of the ribbons. These ribbons crystallize in a partially ordered B2 phase structure. The martensitic structural transition temperature (TM) decreases from 270 K for x = 0 to 175 K for x = 2 with increasing B content. A further increase in B content results in an increase of TM to 268 K for x = 4. The peak value of positive magnetic entropy change (ΔSM) decreases from 20.2 J/kg K for x = 0 to 2.8 J/kg K for x = 4 for a magnetic field change H = 50 kOe. The values of exchange bias field (HE) and the coercivity (HC) change from 258 Oe and 192 Oe to 397 Oe and 600 Oe, respectively, as x is increased from 0 to 4. The phenomena are attributed to the change of exchange interactions in B-substituted Ni-Mn-In ribbons due to the change of distance between Mn atoms.

Dynamic response of exchange bias in graphene nanoribbons

The dynamics of magnetic hysteresis, including the training effect and the field sweep rate dependence of the exchange bias, is experimentally investigated in exchange-coupled potassium split graphene nanoribbons (GNRs). We find that, at low field sweep rate, the pronounced absolute training effect is present over a large number of cycles. This is reflected in a gradual decrease of the exchange bias with the sequential field cycling. However, at high field sweep rate above 0.5 T/min, the training effect is not prominent. With the increase in field sweep rate, the average value of exchange bias field grows and is found to follow power-law behavior. The response of the exchange bias field to the field sweep rate variation is linked to the difference in the time it takes to perform a hysteresis loop measurement compared with the relaxation time of the anti-ferromagnetically aligned spins. The present results may broaden our current understanding of magnetism of GNRs and would be helpful in establishing the GNRs-based spintronic devices.

Origin of the reduced exchange bias in an epitaxial FeNi(111)/CoO(111) bilayer

We have employed Soft and Hard X-ray Resonant Magnetic Scattering and Polarised Neutron Diffraction to study the magnetic interface and the bulk antiferromagnetic domain state of the archetypal epitaxial Ni$_{81}$Fe$_{19}$(111)/CoO(111) exchange biased bilayer. The combination of these scattering tools provides unprecedented detailed insights into the still incomplete understanding of some key manifestations of the exchange bias effect. We show that the several orders of magnitude difference between the expected and measured value of exchange bias field is caused by an almost anisotropic in-plane orientation of antiferromagnetic domains. Irreversible changes of their configuration lead to a training effect. This is directly seen as a change in the magnetic half order Bragg peaks after magnetization reversal. A 30 nm size of antiferromagnetic domains is extracted from the width the (1/2 1/2 1/2) antiferromagnetic magnetic peak measured both by neutron and x-ray scattering. A reduced blocking temperature as compared to the measured antiferromagnetic ordering temperature clearly corresponds to the blocking of antiferromagnetic domains. Moreover, an excellent correlation between the size of the antiferromagnetic domains, exchange bias field and frozen-in spin ratio is found, providing a comprehensive understanding of the origin of exchange bias in epitaxial systems.

Exchange bias in nanoscale antidot arrays

Exchange bias effects have been systematically investigated in nanoscale Cu (10 nm)/Ni80Fe20 (30 nm)/Ir75Mn25 (30 nm)/Cu (2 nm) multilayer antidot arrays. The antidot arrays exhibit asymmetric and shifted hysteresis loops along the induced exchange bias direction, with higher coercivity and exchange bias field values as compared to a continuous film deposited under identical conditions. The evolution in exchange bias field with increasing antidot diameter is ascribed to the constraints imposed on the domain size in the Ir75Mn25 layer and reduced ferromagnetic-ferromagnetic interactions in the Ni80Fe20 layer.

Depth sensitive exchange coupling in top and bottom pinned spin valve structures

AbstractTop and bottom pinned spin valve structures have been fabricated using rf magnetron sputtering to study the depth sensitive exchange coupling. M‐H curves of both the configurations in as‐deposited and annealed forms have been measured by vibration sample magnetometry (VSM) and transverse Kerr effect spectrometry (TKE) using DC and AC magnetic fields, respectively. The TKE signal was also examined as a function of wavelength in the range from 300‐800 nm, to obtain data from the full length of the bottom NiFe free layer covering either side of the interface. Annealing of the samples brings in higher values of exchange bias field compared to as‐deposited samples perhaps due to improved uniformity in exchange conditions. The TKE data at 500 nm wavelength point towards energetically favourable spin structure at the pinned interface. Wavelength dependence of the TKE data shows an anamolous trend close to the NiFe‐Cu (seed layer) inteface, which was attributed to a periodic Cu diffusion assisted non‐specular reflection (diffraction) component. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)