Nonmagnetic Ga Research Articles

Dilution of helical antiferromagnetic matrix of CaMn7O12 under nonmagnetic Ga[formula omitted] doping

The work reports dilution studies on antiferromagnetic CaMn7O12. Introduction of nonmagnetic ion in an antiferromagnetic matrix changes the magnetic properties in an interesting way. The study becomes significant due to the fact that remarkable increase in magnetization is observed as a result of substitution of a few of the magnetic Mn ions with the nonmagnetic Ga ion. For 5% doping of Ga, the magnetization value becomes nearly thrice of the un-doped CaMn7O12. A sequential decrease in antiferromagnetic ordering transition temperature is also observed with increasing Ga percentage in the parent compound. The solid solubility limit of Ga in the matrix is found to be nearly 5%, above which it start showing impurity peaks. Experimental results are well complemented with the Density functional theory (DFT) based calculations. Theoretical calculations are carried out on (CaMn7O12)3 unit cell with one Ga atom doped at different Mn sites resulting around 5% doping concentration. Besides identifying the most favourable doping site for Ga, results indicate a reduction of bulk band gap and significant increase in magnetization, both of which are in agreement with the experimental results.

Magnetic compensation in sputtered ferrimagnetic Mn 4−x Ga x N thin films

Fully compensated ferrimagnets are attracting increasing attention for spintronics. Here we report a series of Mn 4−x Ga x N ferrimagnetic thin films grown on (100)-oriented MgO by magnetron sputtering. A small tetragonal distortion with c/a = 0.99 leads to perpendicular magnetic anisotropy with a [001] easy axis. The magnetisation decreases with increasing Ga content up to x = 0.18, where the magnetic moment is close to zero at room temperature. It increases with further increase of x, indicating the magnetic compensation composition has been crossed and the dominant sublattice has switched from Mn on the corner sites, where it is progressively replaced by nonmagnetic Ga, to noncollinear Mn on the face-centered sites. Compensation found at 235 K in a remanent scan of the x = 0.18 film is confirmed by measurements of the anomalous Hall effect and interpolation of the inverse coercivity. This work establishes the conditions for thin film growth of Mn 4−x Ga x N that could be used for room-temperature ferrimagnetic spintronics. The behaviour of thin films is compared with that of bulk material.

X-ray magnetic circular dichroism of Mn4−xGaxN epitaxial thin films confirming ferrimagnetic-ferromagnetic phase transition by nonmagnetic Ga doping

Researchers have focused on anti-perovskite Mn4N-based ferrimagnets as potential candidates for spintronic applications since these films have a small magnetization and exhibit perpendicular magnetic anisotropy. Magnetic compensation (or angular momentum compensation) in impurity-doped Mn4N at room temperature has attracted particular attention because the magnetization switching can be facilitated in the vicinity of such compensation compositions. In this study, we grew Mn4−xGaxN (x = 0.0–1.9) epitaxial thin films on SrTiO3(001) substrates by molecular beam epitaxy and evaluated their crystallinity and surface conditions. The magnetic properties of the grown films were also examined and a sign reversal of anomalous Hall resistivity and hysteresis loops was observed between x = 0.1 and 0.3 at room temperature by magneto-optical Kerr effect microscopy. X-ray magnetic circular dichroism measurement revealed that the magnetic moment of face-centered Mn at x = 0.3 was reversed to be parallel to that of Mn at corner sites, suggesting that the ferrimagnetic-ferromagnetic phase transition occurred with nonmagnetic Ga doping.

Gallium induced effect on magnetic, magnetostrictive and electrical properties of sintered NiFe2O4

This study investigates how the incorporation of Ga ions into the tetrahedral coordination sites affects the magnetic, magnetostrictive, and electrical properties of sintered NiFe2O4. All characterization was performed on the sintered NiFe2-xGaxO4 samples, which were synthesized using the autocombustion method. The sintered samples exhibit a single phase, wherein the lattice parameter decreases, and the particle size increases with the augmentation of Ga-content within the Ni-ferrite lattice. Saturation magnetization (MS) was found to be higher for x = 0.25 compared to the parent sample (x = 0), while for x = 0.5, MS was slightly lower than that of the parent sample. Both coercivity (HC) and Curie temperature (TC) exhibited a decrease with increasing 'x,' which can be attributed to the weakening of superexchange interactions (A-O-B) due to the presence of non-magnetic Ga ions. Furthermore, the maximum magnetostriction (λmax) also decreased with increasing 'x,' reflecting a magnetic dilution effect within the system. Electric modulus analysis of the dielectric response and the Jonscher power law fits AC conductivity propounded the long-range hoping for charge transportation. Also, the Cole-Cole fit of impedance spectra showed a combined effect of electrode-grain boundary, grain interior, and grain-grain boundary.

Evolution of magnetic surfboards and spin glass behavior in (Fe1−p Ga p )2TiO5

The unusual anisotropy of the spin glass (SG) transition in the pseudobrookite system Fe2TiO5 has been interpreted as arising from an induced, van der Waals-like, interaction among magnetic clusters. Here we present susceptibility () and specific heat data () for Fe2TiO5 diluted with non-magnetic Ga, (Fe1−p Ga p )2TiO5, for disorder parameter = 0, 0.11, and 0.42, and elastic neutron scattering data for = 0.20. A uniform suppression of is observed upon increasing , along with a value of that increases as decreases, i.e. We also observe in the low temperature limit. The observed behavior places (Fe1−p Ga p )2TiO5 in the category of a strongly geometrically frustrated SG.

Assessing the stability of Kagome D019-Mn3Ga (0001) surfaces: A first-principles study

Using non-collinear spin-polarized first-principles calculations, we have investigated the properties of the hexagonal D019 (0001) Mn3Ga surface. Two different surface terminations were considered: type-1 and type-2, with opposite chiralities. In the case of pristine surfaces, the Kagome triangular AFM character remains on the surface and in inner layers, with a slight increase in the surface magnetic moments due to the low coordination of the surface atoms. An increase in the remnant out-of-plane FM character compared to the bulk is also noticed. The effect of Ga or Mn vacancies on both surfaces was also investigated. Ga vacancies in the 2nd monolayer are more stable than in other layers. Such vacancies distort the triangular AFM configuration of the neighboring layers. Despite this, the AFM layer-by-layer nature remains. Conversely, Mn vacancies stabilize in the most exposed layer. In this case, the neighboring layers completely lose the triangular alignment. However, Mn atoms rearrange to preserve the AFM layer-by-layer character. Upon evaluating the thermodynamic stability of these surfaces, we observe that the pristine Kagome AFM magnetic surfaces are the most stable. Ga vacancies are the least stable configurations because they break down the super-exchange interaction that holds the Kagome magnetic arrangement. Finally, our calculations show that the Kagome magnetic arrangement at the surface is stabilized by both the magnetic (Mn) and non-magnetic (Ga) atoms. Therefore, it is expected that D019-Mn3Ga will not present low-index reconstructions induced by vacancies.

Unravelling the linear and biquadratic magnetoelectric coupling in Ba0.95Sn0.05Ti0.95 Ga0.05O3 – CoFe1.8Ga0.2O4 particulate multiferroic composites

Since multiferroic composites have substantially stronger magnetoelectric coupling between the order parameters than the single-phase multiferroics, they are more interesting prospects for next-generation multi-state memories and spintronic devices. In light of this, the current work outlines the fabrication of ferroelectric perovskite BaTiO3 and ferrimagnetic spinel CoFe2O4-based particulate multiferroic composites with general formulla (1-x) Ba0.95Sn0.05Ti0.95 Ga0.05O3 – x CoFe1.8Ga0.2O4 (x = 0.04, 0.08 & 0.12). At room temperature, the gallium and tin doping enhanced the dielectric properties of BaTiO3 (ε ´ =9200), and particulate composite (ε ´ =6000) with 12% of CoFe1.8Ga0.2O4 phase. In the same composite, the reduced leakage current density of 3.4 μA/cm2 and improved magnetoelectric properties, with linear and quardatic coupling coefficients of 3.41 mVcm−1Oe−1 and 3.4 × 10−4 mVcm−1Oe−2 were achieved. In composites with a larger magnetic phase, the decrease in cell volume and increased tetragonality produces the compressive strain, that in turn improves the ME coupling. Diffused ferroelectric transitions were ascertained by using the Curie- Weiss Law. Enhanced dielectric properties are linked to decrease in hopping and bond lengths, caused by the incorporation of non-magnetic Ga3+ ions in the CoFe2O4 lattice. A reduction in leakage current density was observed on Sn doping. The calculated square-ness ratios reveal an ordered multi-domain structure. Improved dielectric response along with linear and biquadratic coupling makes these Sn and Ga doped BaTiO3-CoFe2O4 particulate composites as potential candidates for magnetoelectric devices.

An Experimental Evaluation of Quenched Fe-Ga Alloys: Structural Magnetic and Magnetostrictive Properties

This study examines the effect of quenching on Fe100-x-Gax (x – 20 & 25) alloys. The long range of D03 ordering causes a minor variation in unit cell, which reduces peak intensity. This existence of D03, coupled with the A2 phase, leads to a decrease in magnetostriction in the quenched 25 at.% Ga alloy, which promotes D03 ordering. An Fe-Ga alloy having 20 at.% Ga that has been quenched possesses the A2 phase, the production of D03 is a first-order transition. Continuous ordering attempts to suppress D03 in 25 at. % Ga alloys were ineffective. Quenched Fe80-Ga20 alloy's saturation magnetization is larger than Fe75-Ga25 alloy. This suggests that lowering the nonmagnetic element Ga promotes saturation magnetization. The rise in material flaws and dislocations is due to the increased Ga content and higher quenching temperature. In a single-phase region, Fe80-Ga20 has the greatest magnetostriction at 85 ppm. Magnetostriction diminishes as Ga content rises to 25%, the D03 structure is responsible for this drop.

Tunable exchange bias in La1.5Sr0.5CoMnO6 double perovskite doped with nonmagnetic Ga ions

The crystal structure, electronic structure, and magnetic behaviors of nonmagnetic Ga ions doped double perovskite La1.5Sr0.5CoMnO6 single phase crystals have been investigated. Different from the traditional magnetic dilution effect of nonmagnetic doping, Ga doping in La1.5Sr0.5CoMnO6 enhances the ferromagnetic (FM) exchange interaction of Co3+-O-Mn3+. Moreover, both conventional and spontaneous exchange bias (EB) effects can be tuned by modulating the Ga doping content, which is accompanied by the variation of the Co3+/4+ and Mn3+/4+ and the effective magnetic moment. The EB field and magnetization can be improved by nonmagnetic Ga3+ doping with content lower than 0.2. The evolution of conventional and spontaneous EB effects in La1.5Sr0.5Co1-xGaxMnO6 can be understood in terms of the unidirectional interface anisotropic coupling between FM/anti-FM, and/or FM/spin glass, which is affected by antisite disorder, spin glass, and the uncompensated coupling between Co and Mn.

The spin reorientation and improvement of magnetocaloric effect in HoCr1-xGaxO3 (0 ≤ x ≤ 0.5)

The effect of non-magnetic Ga3+ ions doping at HoCrO3 (HoCr1-xGaxO3, 0 ≤ x ≤ 0.5) on the crystal structure, electronic structure, Raman spectra, and magnetic behaviours were systematically investigated. Most strikingly, a new spin-reorientation transition (Γ2 → Γ4 →Γ2) is triggered by Ga3+ doping in HoCrO3, and the spin configuration of Γ4 is obviously displayed in ZFC and FC curves when x > 0.2. According to the XRD analysis, Ga3+ doping reduces the octahedral distortion and changes the lattice parameters, CrO and HoO bond lengths, and a turning point occurs at x = 0.2. Raman spectra further give evidence of the structural changes and suggest that spin-phonon coupling can be mediated by Ga3+ doping, illustrating the weakened effect of Ga3+ doping on the Ho and Cr interaction. The dilution of the competition between CrCr canted antiferromagnetic coupling and Ho-Cr antisymmetric coupling results in the appearance of spin configuration Γ4. Moreover, the Griffiths phase can also be observed and gradually suppressed with doping. These complex magnetic transitions in HoCr1-xGaxO3 are given in a magnetic phase diagram. From the application point of view, Ga3+ doping also improves the magneto-caloric effect (MCE) and refrigerant capacity (-ΔSM = 10.74 J/KgK, and the RC is 416 J/K at 7 T and 10 K for HoCr0.6Ga0.4O3), which sheds some light on how to optimize the MCE properties.

Half-metallic ferromagnetism in Ga1-xCoxP (x = 0.125, 0.25, 0.75, and 1) alloys: An ab-initio study

III-V compounds belong to one of the most used materials in the technological applications. The doping of transition metals can induce magnetic properties in III-V for the use in spintronics applications. Effect of Co doping with different concentrations (0.125, 0.25, 0.75, and 1) on the physical properties of GaP is investigated using the spin dependent density functional theory. The equilibrium structural parameters such as the lattice constant (a0), the bulk modulus (B0) and the first pressure-derivative of the bulk modulus (B’) are optimized for all these alloys. The calculations of the electronic properties for the Ga1-xCoxP alloys at their equilibrium lattice parameters disclose that all Ga0.875Co0.125P, Ga0.75Co0.25P, Ga0.25Co0.75P, and CoP alloys are complete half-metallic materials. The magnetic properties show that the total magnetic moment for all Ga0.875Co0.125P, Ga0.75Co0.25P, Ga0.25Co0.75P, and CoP alloys has integer value. The p-d hybridization reduces the atomic magnetic moment of Co atom from its free space charge value of 2μB and creates weak local magnetic moments on the nonmagnetic Ga and P sites. Furthermore, the s(p)-d exchange coupling constants N0α and N0β constants are computed to understand role of exchange splitting process in conduction and valence bands. The high spin polarization and originating the ferromagnetism in GaP by the doping of Co can be valuable systems for the use in spin based applications in various electronic devices.

Destruction of long-range magnetic order in an external magnetic field and the associated spin dynamics in Cu2GaBO5 and Cu2AlBO5 ludwigites

The quantum spin systems Cu$_2$M'BO$_5$ (M' = Al, Ga) with the ludwigite crystal structure consist of a structurally ordered Cu$^{2+}$ sublattice in the form of three-leg ladders, interpenetrated by a structurally disordered sublattice with a statistically random site occupation by magnetic Cu$^{2+}$ and nonmagnetic Ga$^{3+}$ or Al$^{3+}$ ions. A microscopic analysis based on density-functional-theory calculations for Cu$_2$GaBO$_5$ reveals a frustrated quasi-two-dimensional spin model featuring five inequivalent antiferromagnetic exchanges. A broad low-temperature $^{11}$B nuclear magnetic resonance points to a considerable spin disorder in the system. In zero magnetic field, antiferromagnetic order sets in below $T_\text{N}$ $\approx$ 4.1 K and ~2.4 K for the Ga and Al compounds, respectively. From neutron diffraction, we find that the magnetic propagation vector in Cu$_2$GaBO$_5$ is commensurate and lies on the Brillouin-zone boundary in the (H0L) plane, $\mathbf{q}_\text{m}$ = (0.45 0 -0.7), corresponding to a complex noncollinear long-range ordered structure with a large magnetic unit cell. Muon spin relaxation is monotonic, consisting of a fast static component typical for complex noncollinear spin systems and a slow dynamic component originating from the relaxation on low-energy spin fluctuations. Gapless spin dynamics in the form of a diffuse quasielastic peak is also evidenced by inelastic neutron scattering. Most remarkably, application of a magnetic field above 1 T destroys the static long-range order, which is manifested in the gradual broadening of the magnetic Bragg peaks. We argue that such a crossover from a magnetically long-range ordered state to a spin-glass regime may result from orphan spins on the structurally disordered magnetic sublattice, which are polarized in magnetic field and thus act as a tuning knob for field-controlled magnetic disorder.

Structural, magnetic, and optical properties of degenerated Ni and (Ga/Zn) co-doped TiO2 nanocomposites

Titanium oxide (TiO2) codoped with Ni-Ga and Ni-Zn nanoparticles were synthesized by the thermal co-precipitation method. The energy-dispersive x‐ray fluorescence, X‐Ray Diffraction, UV–visible absorption spectroscopy, and magnetization methods were performed to study the elemental content, crystalline structure, optical and magnetic properties, respectively. The roadmap of the present work is to explore the conditions of fabrication of dilute magnetic semiconductors, TiO2. It was established that the hydrogenation of the host-doped samples is required to create ferromagnetic properties. It was reported that the effect of doping with non-magnetic Ga3+ and Zn2+ ions created magnetic properties in the hydrogenated Ni-doped TiO2. Some optical properties of undoped and host TiO2 nanopowders were investigated using the diffuse reflectance spectroscopy (DRS) method. The higher magnetic energy observed with Ni/Ga-co-doped TiO2 was reported and discussed by itinerant electrons.

Influence of Ga3+ ion dopant on the structure and magnetic properties of YCrO3

In this work, Ga3+ doped YCr1-xGaxO3 (x = 0, 0.1, 0.2 and 0.3) polycrystalline samples were prepared by solid state reaction method and their crystal structure, morphology, internal defect, specific heat and magnetic properties were studied. The results show that the lattice constants, lattice volume and particle size increase, while Y/Cr–O bond constant decreases with replacing Cr3+ by Ga3+. The positron annihilation spectrum (PAS) measurement shows that cation vacancy defect exists in all samples and the internal defect concentration fluctuates slightly with increasing of Ga3+ ions doping concentration. For low doping content, an additional magnetization anomaly emerges in the zero-field-cooling curves measured in H = 1000Oe. With the increase of magnetic field, the anomaly can be well suppressed. Simultaneously, for the specific heat curve peak cannot be observed at the corresponding temperature. These results imply the establishment of short-range magnetic order above the antiferromagnetic transition temperature (TN) due to the dilution effect of nonmagnetic Ga3+ doping.

Sharp steps in magnetization, magnetoresistance, and magnetostriction in Pr0.6Sr0.4Co1−yGayO3

We report the magnetization, magnetoresistance, and magnetostriction in polycrystalline Pr0.6Sr0.4Co1−yGayO3 (y = 0.0–0.3) samples. Upon substitution of the non-magnetic Ga3+ cation for Co3+, the low temperature ground state transforms from a ferromagnetic metal for y = 0 to a cluster glass type semiconductor for y ≥ 0.2. The field-dependent magnetization, magnetoresistance, and magnetostriction for y ≥ 0.2 show reversible abrupt steps for both positive and negative magnetic fields at T ≤ 3 K, whereas all these quantities vary smoothly with the magnetic field above 4 K. Such steps in all three distinct physical quantities were never reported earlier in perovskite cobaltites, and they differ from observations made in manganites and intermetallic alloys. It is suggested that field-induced avalanche flipping of ferromagnetic clusters is the origin of observed steps in all these three quantities.

Study of structural, optical and magnetic properties of hydrogenated Ni and (Ga, Zn) co-doped SnO2 nanocomposites

Tin oxide (SnO2) co-doped with 3%Ni - 5%Ga and 3%Ni - 5%Zn nanocomposites were manufactured by a co-precipitation method. The samples were characterized by several methods. Energy dispersive x‐ray fluorescence, X‐Ray Diffraction, UV–visible absorption spectroscopy, and magnetization measurements were performed to study the elemental analysis, crystal structure, optical band gap and magnetic properties, respectively. The present research is planned to investigate the conditions necessary to fabricate the dilute magnetic semiconductor, SnO2 of nanocomposites. It was found that the hydrogenation of the host samples is a necessary action that should be processed to create ferromagnetic properties. The effect of doping of non-magnetic Ga3+ and Zn2+ ions on the generated magnetic properties in the hydrogenated Ni-doped SnO2 nanopowder was investigated and reported. The optical bandgap of the SnO2 nanopowders was studied by diffuse reflectance spectroscopy (DRS) and found it was redshifted with Ni, Ga, and Zn doping. The higher magnetic energy observed with Ni and Ga codoped SnO2 was reported and discussed.

Formation mechanism of tetragonal nanoprecipitates in Fe–Ga alloys that dominate the material's large magnetostriction

Up to now, the formation mechanism of tetragonal nanoprecipitates that may dominate the large magnetostriction of Fe–Ga alloys remains unclear. Here we found that both L60- and D022-type face-centered-tetragonal nanoprecipitates are precursors of the face-centered-cubic L12 equilibrium phase, as identified in the isothermally-aged Fe73Ga27 and Fe74Ga26 alloys, respectively. The L60 phase is formed due to Ga ordering along -A2 direction and simultaneous lattice distortion. The D022 phase is formed via diffusionless lattice distortion when the D03 ordering degree is sufficient high. These findings may provide a microstructural basis for the large magnetostriction induced by soluting nonmagnetic Ga into body-centered-cubic Fe.

Significant Enhancement of Spin Polarization and Magnetism in the Surface State of Full‐Heusler Structural Cr2CoGa

For pristine full‐Heusler structural L21‐Cr2CoGa thin films, full‐potential ab initio density‐functional theory (DFT) simulations within the generalized gradient approximation (GGA) are used to investigate the structural stability, the electronic and magnetic properties of the two possible (001) surfaces. It is found that: 1) the spin polarization at the CoGa‐terminated (001) surface state decreases to 27% from 69% in bulk due to the screening of the p‐electrons of the nonmagnetic sp atom Ga at surface; 2) the spin polarization at the Cr1Cr2‐terminated (001) surface state is remarkably increased to 92% owing to the much lower density of states of minority‐spin surface states at the Fermi level. Cr1 (Cr2) atomic magnetic moments at the Cr1Cr2‐terminated (001) surface are greatly increased compared to bulk. Furthermore, it is unveiled that the Cr1Cr2‐terminated (001) surface is more stable than the CoGa‐terminated (001) for the lower surface energy over the whole effective chemical potential. This surprising report indicates that the full‐Heusler structural L21‐type Cr2CoGa thin films are promising candidates for the next‐generation spintronic materials.

Effect of nonmagnetic substitution on the magnetic correlation of the frustrated Ca3CoMn1-xGaxO6 (0≤x≤0.2)

For the spin-chain compound Ca3CoMnO6, the perfect Co/Mn ionic order causes the lost of ↑↑↓↓ long-range antiferromagnetic order. The lost long-range magnetic order results in the emergence of short range magnetic correlation interaction, forming the so called “order by disorder” phenomenon. In present paper, nonmagnetic Ga3+-doped Ca3CoMn1-xGaxO6 compounds were prepared. The influence of Ga3+ substitution on the structure and magnetic order of Ca3CoMn1-xGaxO6 were investigated. It is found that the solid solubility of Ga3+ cation in Ca3CoMn1-xGaxO6 is 0.2 < x < 0.3. With introducing of Ga3+ cation, the oxidation state of some Co cations changes from Co2+ to Co3+. Magnetization measurements reveal that doped with nonmagnetic Ga3+ weakens the formation of short range magnetic order and enhances the antiferromagnetic transition temperature. As a result, more robust long rang antiferromagnetic order is established and the transition field that causes the ↑↑↓↓ spin state of Co–Mn–Co–Mn chain to ↑↑↓↑ state increases obviously. Meanwhile, the shortened short range magnetic correlation in Ga3+ doped Ca3CoMn1-xGaxO6 can be driven more easily by the thermal activation energy and a quicker dynamic behavior was observed in time windows.

Effect of doping of Co, Ni and Ga on magnetic and dielectric properties of layered perovskite multiferroic YBaCuFeO5

YBaCuFeO5 is one of the interesting multiferroic compounds, which exhibits magnetic ordering and dielectric anomaly above 200 K. Partial substitution of Fe with other magnetic and non-magnetic ion affects the magnetic and the structural properties of the system. We report detailed investigation of structural, magnetic and dielectric properties of YBaCuFe0.85M0.15O5 (M = Co, Ni and Ga). We observed that the partial replacement of Ni and Co in place of Fe, results in magnetic dilution and broadening of the magnetic transition and shifting towards lower temperature. The replacement of Fe with non-magnetic Ga also results in shifting of the magnetic transition to the lower temperature side. The observed dielectric relaxation behavior in these compounds is due to the charge carrier hoping. This study highlights the impacts of magnetic and non-magnetic doping at the magnetic site on magnetic and dielectric properties in layered perovskite compound YBaCuFeO5.