Nonmagnetic Ga Research Articles

Site dilution and charge disorder effect on physical properties in SrRu1−xGaxO3

Here, we report an evolution of structural, magnetic and transport behavior in doped SrRu1−xGaxO3 (x 0.2). The nonmagnetic dopant Ga3+ (3d10) not only acts for magnetic site dilution in SrRuO3 but also modifies the Ru charge state and electronic density. Our studies show that Ga3+ substitution does not affect the original orthorhombic- Pbnm structure of SrRuO3 which is due to its matching ionic radii with Ru4+ . However, Ga3+ has a substantial effect on the magnetic behavior of SrRuO3 where it decreases both magnetic moment as well as magnetic transition temperature . Further, this dilution induces Griffiths phase behavior across and cluster-glass behavior at low temperature with higher concentration of doping. The magnetic critical exponent increases with x due to this site dilution effect. The Ga3+ induces an insulating state in SrRuO3 with x > 0.05. The charge transport in paramagnetic as well as in insulating state of samples can be well described with Mott’s modified variable-range-hopping model. The metallic charge transport just below in SrRuO3 obeys Fermi liquid behavior which breaks down at low temperature. We further find a correlation between field dependent magnetoresistance and magnetization through power-law behavior over the series.

Magnetic properties of Single Crystal GaFeO3

Abstractκ-Al2O3-type GaFeO3 is a promising multiferroic material due to the coexistence of a large spontaneous magnetization and polarization near room temperature. In the current study, we present the magnetic properties of single crystalline GaFeO3 and compare it with that of ε-Fe2O3. Magnetic measurements revealed that spontaneous magnetization appears below 540 K in two steps, similar to that reported for ε−Fe2O3. Partial magnetic ordering takes place at 540 K (TN1), with Fe3+ ions in two distorted octahedral sites ordering antiparallel to one another. Upon further cooling at 200 K (TN2), the remaining Fe3+ ions in regular octahedra and tetrahedra order antiparallel to one another. Substitution of Ga for Fe in ε-Fe2O3 leads to a decrease in TN1 and TN2 from 850 to 540 K and from 480 to 200 K, respectively, caused by a dilution of magnetic Fe by nonmagnetic Ga and preferential site occupation of Ga.

Study of Structural, Electronic, and Magnetic Properties of Cubic Lanthanide Based on Oxide Perovskite-Type NdGaO3

Based on the density functional theory (DFT), the full-potential linearized augmented plane wave with local orbital (FP-L/APW+lo) technique is now employed in this approach to understand the structural, electronic, and magnetic properties of simple cubic oxide perovskite NdGaO3 compound. In all this investigation, the exchange-correlation (XC) energy is selected in the framework of spin-polarized generalized gradient approximation (spin-GGA). The structural analysis unveils that the ferromagnetic (FM) phase is the stable ground state of the cubic NdGaO3 compound, where the equilibrium lattice parameters (lattice constant (a0), bulk modulus (B0), and its first pressure derivative (B′)) are determined in both FM and paramagnetic (PM) phases. The spin-polarized electronic properties (band structure and density of states) of the cubic NdGaO3 oxide perovskite are studied under the platform of equilibrium lattice parameters; this investigation demonstrates the half-metallic behavior of the studied cubic NdGaO3 compound because the spin-up case displays the metallic nature, whereas the semiconducting character is observed in spin-down case. The magnetic properties reveal that the total magnetic moment of the cubic NdGaO3 compound is equal to 3 μB and its contribution is mostly generated by Nd atoms, whereas feeble local magnetic moments are installed in non-magnetic Ga and O sites. Through the electronic and magnetic results, we conclude that the cubic perovskite NdGaO3 compound is classified as a half-metallic ferromagnetic material.

Cr2.37Ga3Se8: A Quasi-Two-Dimensional Magnetic Semiconductor.

We present a novel magnetic semiconductor, Cr2.37Ga3Se8, synthesized by partially replacing magnetic Cr3+ in antiferromagnetic Cr5+δSe8 with nonmagnetic Ga3+. The crystal structure of Cr2.37Ga3Se8 was determined by both powder and single-crystal X-ray diffraction. The title compound crystallizes in a monoclinic structure with space group C2/ m (No. 12). In Cr2.37Ga3Se8, the Cr atoms are surrounded by 6 Se atoms and form filled octahedral clusters, while Ga atoms are centered in the Se4 tetrahedral clusters. The two kinds of clusters pack alternatingly along the c-axis, which results in a quasi-two-dimensional layered structure. The magnetization ( M) measurement shows the development of short-range ferromagnetic coupling below the Curie-Weiss (CW) temperature θCW ∼ 92 K, evidenced by the nonlinear field dependence of M. However, the magnetic susceptibility exhibits a peak at low fields at ∼18 K, indicating the existence of an antiferromagnetic interaction as well. Electronic structure calculations using the WIEN2k program in the local spin density approximation indicate that the magnetism arises exclusively from local moments of the Cr atoms. The electrical resistivity measurement of the Cr2.37Ga3Se8 sample confirms that this material is a semiconductor with the band gap ∼0.26 eV. Meanwhile, the experimental band gap (∼0.26 eV) is close to the theoretical prediction using the WIEN2k program (∼0.35 eV).

Effect of Cr substitution on ferrimagnetic and ferroelectric properties of GaFeO3 epitaxial thin films

To control the properties of multiferroic materials, substitution of magnetic elements is a useful technique. In this study, we fabricated GaCrxFe1−xO3 and Ga1−yCryFeO3 films by substituting Cr3+ (3d3) ions in GaFeO3 for magnetic Fe3+ (3d5) and nonmagnetic Ga3+ (d10) sites, respectively. The effect of the Cr substitution on the magnetic and dielectric properties was systematically investigated. The obtained GaCrxFe1−xO3 and Ga1−yCryFeO3 films (x ≤ 1/4 and y ≤ 1/2) simultaneously exhibit ferrimagnetism and ferroelectricity. For the GaCrxFe1−xO3 films, the magnetic transition temperature (TC) and magnetic anisotropy decrease with increasing x. On the other hand, for the Ga1−yCryFeO3 films, TC increases with increasing y. Unlike the GaFeO3 film, the Cr-substituted GFO films show a peak in the magnetization versus temperature curves and exhibit a sudden decrease in the coercive field near the peak, probably due to the formation of Fe3+–O–Cr3+ coupling which prefers to form ferromagnetic interactions in the antiferromagnetic Fe3+–O–Fe3+ networks. Furthermore, we found that the Cr-substituted GaFeO3 films show out-of-plane ferroelectricity at room temperature.

Role of Gallium in the charge transport mechanisms for La0.67Ca0.33Mn1–xGaxO3 manganites

In this communication, we report the results of the studies on structural, transport and magnetoresistance (MR) properties of nonmagnetic Ga – substituted La0.67Ca0.33Mn1–xGaxO3 (LCMGO) manganites synthesized using conventional ceramic route. Rietveld refined XRD patterns shows that all the samples possess single phasic nature without any detectable impurity. Resistivity behavior shows a systematic variation with Ga3+ – content (x) while metal to insulator transition temperature (TP) shifts towards lower temperature which has been discussed in the light of zener double exchange (ZDE) mechanism and magnetic lattice distortion due to nonmagnetic ion substitution. Observation of low temperature resistivity minima behavior has been explained in the context of electron – electron scattering mechanism. Various transport models and mechanisms have been employed to understand the charge transport in metallic and semiconducting regions of all LCMGO samples. Temperature and Field dependent MR studies reveal intrinsic and extrinsic MR contributions in presently studied LCMGO manganites.

Influence of nonmagnetic Ga ions on the magnetoelectric coupling in CuFe1−xGaxO2

The magnetic properties and dielectric polarization of CuFe1−xGaxO2 with various nonmagnetic Ga3+ doping levels have been measured in a wide magnetic field region, in which the observed experiment results have been explained by the consequence of the change in exchange interaction, dilution effect, and partial reduction of spin frustration. Compared with pure CuFeO2, doped nonmagnetic Ga3+ ions have an important effect on magnetization and polarization behavior and lead to an enhanced magnetoelectric coupling, especially, an enhanced spontaneous polarization has been observed in the doping amount of 0.02 and 0.05. This magnetoelectric effect appears mainly in the ferroelectric incommensurate magnetic phase region due to the noncollinear magnetic structure with a proper helical order in the CuFeO2. Based on the magnetization and polarization data, a magnetic phase diagram of temperature, magnetic field, and the doping amount are obtained.

Structural disorder and elementary magnetic properties of triangular lattice ErMgGaO4 single crystals

The single crystal growth, structure, and basic magnetic properties of ErMgGaO4 are reported. The structure consists of triangular layers of magnetic ErO6 octahedra separated by a double layer of randomly occupied non-magnetic (Ga,Mg)O5 bipyramids. The Er atoms are positionally disordered. Magnetic measurements parallel and perpendicular to the c axis of a single crystal reveal dominantly antiferromagnetic interactions, with a small degree of magnetic anisotropy. A weighted average of the directional data suggests an antiferromagnetic Curie Weiss temperature of approximately −30 K. Below 10 K the temperature dependences of the inverse susceptibilities in the in-plane and perpendicular-to plane directions are parallel, indicative of an isotropic magnetic moment at low temperatures. No sign of magnetic ordering is observed above 1.8 K, suggesting that ErMgGaO4 is a geometrically frustrated magnet.

Tuning the antiferromagnetic helical pitch length and nanoscale domain size in Fe3PO4O3 by magnetic dilution

The insulating magnetic material Fe3PO4O3 features a non-centrosymmetric lattice composed of Fe^{3+} triangular units. Frustration, due to competing near neighbor ($J_1$) and next nearest neighbor ($J_2$) antiferromagnetic interactions, was recently suggested to be the origin of an antiferromagnetic helical ground state with unusual needle-like nanoscale magnetic domains in Fe3PO4O3. Magnetic dilution is shown here to tune the ratio of these magnetic interactions, thus providing deeper insight into this unconventional antiferromagnet. Dilution of the Fe^{3+} lattice in Fe3PO4O3 was accomplished by substituting non-magnetic Ga^{3+} to form the solid solution series Fe_{3-x}Ga_xPO4O3 with $x = 0.012, 0.06, 0.25, 0.5, 1.0, 1.5$. Magnetic susceptibility and neutron powder diffraction data from this series are presented. A continuous decrease of the both the helical pitch length and the domain size is observed with increasing dilution up to at least $x = 0.25$, while for $x \ge 0.5$, the compounds lack long range magnetic order entirely. The decrease in the helical pitch length with increasing $x$ can be qualitatively understood by reduction of the ratio of $J_2/J_1$ in the Heisenberg model, consistent with mean field considerations. Intriguingly, the magnetic correlation length in the $ab$ plane remains nearly equal to the pitch length for each value of $x \le 0.25$, showing that the two quantities are intrinsically connected in this unusual antiferromagnet.

Evidence for lattice softening of the Fe-Ga magnetostrictive alloy: Stress-induced local martensites

The over tenfold magnetostriction enhancement by soluting nonmagnetic Ga into body centered cubic (BCC) Fe has been ascribed to crystal lattice softening, which indicates that the Fe-Ga solid solution lies in the crossover of martensitic transformation. Identifying the martensitic phase then becomes essential. Here we report the stress-induced local six-layer modulated monoclinic (6M) martensites in a Fe79Ga21 alloy solution-treated at 1373K. Although X-ray diffraction (XRD) and magnetic measurements reveal that the bulk sample exhibits BCC average structure, the transmission electronic microscopy (TEM) characterizations however show that the mechanically grinded foil sample contains local 6M phase. First principal calculations suggest that low formation energy barrier between the ordered D03 and the 6M phases are responsible for the stress-induced structural transformation. Our work provides evidence for the lattice softening of Fe-Ga solid solution, adding important insight into understanding the origin of its extraordinary magnetostriction enhancement.

Magnetic coupling in nonmagnetic metal adsorption on arsenene monolayer: Ab initio study

The structural, electronic and magnetic properties of adsorbed arsenene monolayer with a series of nonmagnetic metal atoms, including Al, Ga, Li, Mg, and Na, are systematically investigated using first-principles calculations. From our calculations, nonmagnetic states appear in the cases of Li, Mg, and Na. The magnetism has been observed for Al and Ga adatoms. Then, we study the magnetic interaction between the moments induced by Al and Ga adatoms. It is found that a p–d exchange-like p-p hybridization results in the ferromagnetic (FM) state. However, when the distance of Ga-Ga or Al-Al is increased, it is found out that the FM interaction has been extremely depressed. This phenomenon can be explained by a simple Heisenberg model. The X-adsorbed (X= Al and Ga) arsenene systems are promising candidates for spintronic devices in the future.

Magnetic Properties in Nonmagnetic Metal Atom Adsorption on SiC Monolayer: First-Principles Study

The structural, electronic, and magnetic properties of adsorbed SiC monolayer with a series of nonmagnetic metal atoms, including Al, Ga, Li, Mg, and Na, are systematically investigated using first-principles calculations. Magnetic behavior shows in the Al-, Ga-, Li-, and Na-adsorbed systems, and both nonmagnetic metals and their neighboring Si/C atoms contribute to the magnetism. Meanwhile, due the most stable structure of Al-adsorbed SiC monolayer, we investigated the magnetic interaction between two Al atoms. A long-range antiferromagnetic (AFM) is always observed as the Al-Al distance increases. Our results show that the two-Al-adsorbed 2D SiC exhibits an AFM order due to the p-p hybridization mechanism.

Lattice Structure and Magnetic Behavior of Ga Ion Doped Multiferroics CaMn<sub>7</sub>O<sub>12</sub>

The lattice structure and magnetism of polycrystalline CaMn7-xGaxO12 (x = 0, 0.1, 0.2, 0.3, 0.4) synthesized by solid state method have been investigated. The refined x-ray diffraction patterns show that a well single phase Ga doped CaMn7O12 crystals can be obtained by solid state method and their lattice structure is rhombohedral with R-3. The lattice parameter a linearly decreases while parameter c linearly increases with increasing doping concentration, leading to a lattice distortion. Magnetic susceptibility and inverse susceptibility as a function of temperature show that CaMn7-xGaxO12 and undoped CaMn7O12 behave the basically identical magnetic characterization, that is, there are two magnetic phase transitions at 90 K and 40 K. And the antiferromagnetic transitional temperature is not obviously influenced by non-magnetic Ga ions doping. However, the magnetization at temperature lower than 40 K is enhanced and there is a new transitional temperature point observed at temperature range between 40 and 90 K, which indicates that Ga ions participate into the magnetic interaction.

Investigation of spin moment in Ga-substituted cobalt ferrite: magnetic Compton scattering and photoemission studies

We have studied the spin-dependent electron momentum density distribution in CoGa x Fe2−x O4 (x = 0.2, 0.3) at a low temperature (8 K) using magnetic Compton scattering technique. Further, the effect of Ga doping on the electronic structure is studied using X-ray photoemission spectroscopy (XPS). It is revealed that doping of Ga substitutes the Fe ions predominantly at tetrahedral (P) site, which promotes a gradual immigration of small amount of Co ions from tetrahedral to octahedral (Q) site. Total spin moment increases remarkably on increasing the doping concentration of nonmagnetic Ga (x = 0 → 0.3) in the base cobalt ferrite. It is seen that major contribution to total spin moment mainly arises from Co ions while itinerant electrons show negative polarization. On Ga doping, spin moment at Fe site increases dramatically with a minor increment at Co site. The increased spin moment is attributed to the increased Q/P occupancy ratio of Fe3+ as well as Co2+ ions as determined using XPS measurements. In contrast, orbital moment does not show such deviations, suggesting that a small amount of Ga doping can enhance the magnetization significantly, without inducing any significant distortion to modify the spin–orbit coupling.

High magnetostriction parameters of sintered and magnetic field annealed Ga-substituted CoFe2O4

Impact of substitution of the non-magnetic ion Ga3+ for Fe3+ on the magnetostriction parameters of CoFe2O4 has been investigated for samples prepared by a tartrate-gel method. All the Ga-substituted compositions in CoGaxFe2-xO4 (0⩽x⩽0.3) showed higher strain sensitivity (dλ/dH), at low magnetic fields, compared to that of the unsubstituted sample. The magnetostriction strain (λ) and dλ/dH of the composition CoGa0.1Fe1.9O4 could be enhanced from −228 to −296ppm and −2.20× 10−9 to −3.55× 10−9m/A, respectively, at low magnetic fields, after magnetic field annealing at 300°C.

Preparation of high magneto-optical performance and crystalline quality Ce1Gd2Fe5−xGaxO12 films on CLNGG substrate crystal

Thin films of Ce1Gd2Fe5−xGaxO12 (Ce,Ga:GIG) were prepared on Gd3Ga5O12 (GGG) and Ca2.90Li0.30Nb1.93Ga2.76O12 (CLNGG) substrates by using radio frequency magnetron sputtering technique. The phase, grain orientation, surface morphology, transmittance, magnetism and magnetic circular dichroism (MCD) properties of films were analyzed. And the effects of lattice mismatch and non-magnetic Ga3+-doping were discussed. The results show that the films with higher crystallized quality and lower stress can be obtained by growing on CLNGG than on GGG. Moreover, the coercive force, magnetization, magneto-optical effect intensity and orientation of film can be effectively regulated by adjusting Ga3+-doped concentration.

Sc2Ga2CuO7: A possible quantum spin liquid near the percolation threshold

Sc$_{2}$Ga$_{2}$CuO$_{7}$ (SGCO) crystallizes in a hexagonal structure (space group: $P$$6$$_{3}/mmc$),\textcolor{black}{{} which can be seen as an alternating stacking of single and double triangular layers. Combining neutron, x-ray, and resonant x-ray diffraction we establish that the single triangular layers are mainly populated by non-magnetic Ga$^{3+}$ ions (85\% Ga and 15\% Cu), while the bi-layers have comparable population of Cu$^{2+}$ and Ga$^{3+}$} ions \textcolor{black}{(43\% Cu and 57\% Ga)}. Our susceptibility measurements in the temperature range 1.8 - 400 K give no indication of any spin-freezing or magnetic long-range order (LRO). We infer an effective paramagnetic moment $\mu_{eff}=1.79\pm0.09$ $\mu_{B}$ and a Curie-Weiss temperature $\theta_{CW}$ of about $-44$ K, suggesting antiferromagnetic interactions between the Cu$^{2+}$($S=1/2$) ions. Low-temperature neutron powder diffraction data showed no evidence for LRO down to 1.5 K. In our specific heat data as well, no anomalies were found down to 0.35 K, in the field range 0-140 kOe.\textcolor{black}{{} The magnetic specific heat, $C_{m}$, exhibits a broad maximum at around 2.5 K followed by a nearly power law $C$$_{m}$$\propto$ $T$$^{\alpha}$ behavior at lower temperatures, with $\alpha$ increasing from }0.3\textcolor{black}{{} to} 1.9\textcolor{black}{{} as a function of field for fields upto 90 kOe and then remaining at 1.9 for fields upto 140 kOe. Our results point to a disordered ground state in SGCO. }

Effect of Ga substitution on magnetocaloric effect in La0.7(Ba, Sr)0.3Mn1−xGaxO3 (0.0≤x ≤0.20) polycrystalline at room temperature

In this paper, we have investigated the effect of the non-magnetic (d10) Ga3+ doping on structural, magnetic and magnetocaloric properties of La0.7(Ba, Sr)0.3Mn1−xGaxO3 (x=0.0, 0.1 and 0.2) manganites prepared by solid state reaction method. The XRD study has revealed that all samples crystallized in the orthorhombic symmetry with Pnma space group. Magnetization measurements have confirmed that when the temperature increases, all the compositions exhibit a ferromagnetic to paramagnetic transition. The substitution of Mn by gallium Ga leads to a tune of the magnetic transition temperature (TC) to room temperature and the Curie temperature decreases from 314K for x=0.0 to 299K for x=0.2. Moreover, the obtained results of the magnetocaloric effect are in accordance with the reported values of other doped manganites, leading to the conclusion that our sample can be used as a magnetic refrigerant at room temperature.Finally, using Arrott plots, the phase transition from ferromagnetic to paramagnetic was found to be of a second order. The second order magnetic phase transition has been confirmed by the construction of the universal curve of the magnetic entropy change.

Spin jam induced by quantum fluctuations in a frustrated magnet

Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr(3+) (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga(3+) impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p > 0.8) and a cluster spin glass for lower magnetic concentration (p < 0.8). This observation indicates that a spin jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood.

Elemental substitution effects in multiferroic R Fe2O4 (R: rare earths)

AbstractWe report the effects of elemental substitutions in multiferroic R Fe2O4 (R: Y, Ho‐Lu, In). The substitution by nonmagnetic Ga3+ at the Fe site, which has not been reported so far, shows a drastic decrease in the ferrimagnetic transition temperature (TN). This is plausibly owing to the suppression of magnetic interactions between Fe ions, based on our previous results of other substituted systems such as R FeCoO4. Dielectric constants near room temperature were comparable to those of R Fe2O4. The suppression of dielectric loss in this system is suitable to application. The R ‐site substitution was also attempted by the large R3+ ions such as Dy3+. The solubility limit was up to ∼10% of R ions. TN was raised by 5‐10 K for Dy3+ substitution. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)