Metal insulator transition with ferrimagnetic order in epitaxial thin films of spinel NiCo2O4

Silwal, Punam; Miao, Ludi; Stern, Ilan; Zhou, Xiaobo; Hu, Jin; Kim, Dae Ho

doi:10.1063/1.3676439

Cited by 83 publications

(88 citation statements)

References 17 publications

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“…Since this metal-insulator transition was typically close to the Curie temperature, they concluded the occurrence of magnetic polarons. Similar observations were also made by Silwal et al 21 However, small-polaron formation due to the interaction with phonons and disappearance of the activation energy at low temperatures is a typical observation for oxides 47 and could be an alternative explanation. Figure 6 shows the change of resistance with temperature for our (Co setup.…”

Section: Resultssupporting

confidence: 73%

“…For the stoichiometric x = 0.33 film, the resistance decreases with temperature over the whole temperature range as it is expected for polaron hopping. This is in contrast to the observations of Bitla et al 19 and Silwal et al 21 despite the resistivity of 0.0014 Ωcm is similar to the values these groups obtained for their 'metallic' (Co 2/3 Ni 1/3 ) 3 O 4 films. One possible explanation for this is the polycrystalline nature of the films.…”

Section: Resultscontrasting

confidence: 57%

“…14,19,21,22,[53][54][55] Most often, (Co 2/3 Ni 1/3 ) 3 O 4 is described as ferrimagnetic resulting from superexchange between Ni ions on the O h site and Co ions on the T d site. 54 However, the various ionic species possible in this material result in many different exchange pairs with negative as well as positive interactions.…”

Section: Resultsmentioning

confidence: 99%

“…For example, Windisch et al 20 reported a room-temperature (RT) resistivity of 0.06 Ωcm for solution deposited films, while they obtained films with a resistivity as low as 0.003 Ωcm by sputtering. Silwal et al 21 fabricated epitaxial (Co 2/3 Ni 1/3 ) 3 O 4 films on MgAl 2 O 4 using pulsed laser deposition (PLD) and observed extremely differing electrical properties depending on the growth temperature. They measured RT resistivity values of about 0.001 Ωcm for films deposited at 250 • C and 0.1 Ωcm for films deposited at 600 • C. Moreover, the resistivity of the films deposited at high temperatures increased exponentially with decreasing temperature, as it is expected in the case of electrical transport by small polarons, while for the films deposited at low temperatures it decreased over a wide temperature range as it is typical for itinerant charge carriers such as classical holes or large polarons.…”

Section: Introductionmentioning

confidence: 99%

“…Similarly, the magnetic nature of (Co 2/3 Ni 1/3 ) 3 O 4 depends strongly on the deposition method and has been shown to be related to the electrical transport mechanism. 19,21,22 Having the eye on the potential applications of semiconducting oxides, atomic layer deposition (ALD) provides us with a number of advantages over other thin-film fabrication techniques. It can be easily scaled up to commercially relevant dimensions and furthermore allows the coating of difficult morphologies and the fabrication of precisely dimensioned heterostructures such as superlattices.…”

Section: Introductionmentioning

confidence: 99%

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Atomic layer deposition of nickel–cobalt spinel thin films

2017

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We report the atomic layer deposition (ALD) of high-quality crystalline thin films of the spinel-oxide system (Co 1−x Ni x ) 3 O 4 . These spinel oxides are ferrimagnetic p-type semiconductors promising for several applications ranging from photovoltaics and spintronics to thermoelectrics. The spinel phase is obtained for Ni contents exceeding thex = 0.33 limit for bulk samples. It is observed that the electrical resistivity decreases continuously with x while the magnetic moment increases up to x = 0.5. This is in contrast to bulk samples where a decrease of resistivity is not observed for x > 0.33 due to the formation of a rock-salt phase. From UV-VIS-NIR absorption measurements, a change from distinct absorption edges for the parent oxide Co 3 O 4 to a continuous absorption band ranging deep into the near infrared for 0 < x ≤ 0.5 was observed. The conformal deposition of dense films on high-aspect-ratio patterns is demonstrated.

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Section: Resultssupporting

confidence: 73%

Section: Resultscontrasting

confidence: 57%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Atomic layer deposition of nickel–cobalt spinel thin films

2017

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Magnetotransport Anomaly in Room‐Temperature Ferrimagnetic NiCo₂O₄ Thin Films

et al. 2018

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While previous studies of NCO have mainly centered on nanostructured and mesoporous materials, [6][7][8]15,16] it is of high research interest to examine the system in the epitaxial thin film form, especially for developing spintronic applications such as spinel-based magnetic tunnel junctions (MTJs). [17,18] To date, reports on high-quality NCO thin films have been scarce and mostly focused on the disorder-driven metal-insulator transition, [3,5,11,14,19,20] while the intrinsic magnetotransport properties in the metallic phase remain uncharted.In this work, we report the magnetotransport anomalies observed in 5-30 unit cell (uc) thick high-quality epitaxial NCO thin films. Below the magnetic ordering temperature, NCO exhibits strong out-of-plane magnetic anisotropy, linear magnetoresistance (MR), and robust anomalous Hall effect (AHE) that persist above room temperature. The longitudinal resistance exhibits a weak temperature dependence that cannot be directly correlated with the magnetic state of the system. The anomalous Hall conductivity (σ xy ) shows an unusual nonmonotonic temperature dependence, which changes sign in the thinner films. The relation between σ xy and the longitudinal conductivity (σ xx ) at the intermediate temperature range points to the dirty metal behavior in conjunction with the contribution from band intrinsic Berry phase effect, while the low-temperature characteristic can be attributed to disorderenhanced electron correlation. Our work provides critical information on how to manipulate the competing energy scales in this system to achieve tailored functionalities for spintronic applications.We deposited high-quality 5-30 uc epitaxial NCO films on (001)-oriented MgAl 2 O 4 (MAO) substrates. The bulk cubic lattice constant of NCO is 8.128 Å, subjecting to a 0.55% compressive strain when grown on MAO (a = 8.083 Å). X-ray diffraction (XRD) measurements show (001) growth with no impurity phases (Figure 1b). The calculated c-axis lattice constant is 8.196 Å, comparable with the reported values for strained films. [11,19] Figure 1c,d shows the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images of a 17 uc NCO film, which reveal a homogeneous inverse spinel structure with high crystallinity. Atomic force microscopy (AFM) measurements show smooth surface morphology in these samples (Figure 1e), with typical root mean square roughness of 2-3 Å.The inverse spinel ferrimagnetic NiCo 2 O 4 presents a unique model system for studying the competing effects of crystalline fields, magnetic exchange, and various types of chemical and lattice disorder on the electronic and magnetic states. Here, magnetotransport anomalies in high-quality epitaxial NiCo 2 O 4 thin films resulting from the complex energy landscape are reported. A strong out-of-plane magnetic anisotropy, linear magnetoresistance, and robust anomalous Hall effect above 300 K are observed in 5-30 unit cell NiCo 2 O 4 films. The anomalous Hall resistance exhibits a nonmonotonic temperature dependence th...

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Manipulate the Electronic and Magnetic States in NiCo₂O₄ Films through Electric‐Field‐Induced Protonation at Elevated Temperature

et al. 2019

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it has been demonstrated recently that the residual water would exist ubiquitously within the ionic liquid (IL) when experiments performed in the air. [11][12][13][14] The water molecular would facilitate the electrochemical reaction through electrolysis into H + and O 2ions, which would then be inserted into materials depending on the polarity of the gating bias [11][12][13][14][15][16][17] (as shown in Figure 1a). Clearly, the electrochemical reaction related modulation is a bulk effect, and therefore its associated charge modulation should not be confined by the 2D limit as the conventional ILG, which is about 10 15 cm −2 at the sample surface. [2][3][4][5][6][7][8] Along these studies, the H + (proton) ion, the smallest and lightest ion, emerges as an ideal candidate to incorporate into materials for the manipulation of band filling via charge neutrality induced electron doping with positively charged proton. [13,18] Besides, protonated materials have tremendous application potential in hydrogen storage [18] and fuel cells. [19][20][21][22] So the study of ILG induced protonation is significant for both fundamental physics (realizing electron doping and phase control) and industry application (discovering new protonated functional materials). It is important to note that although the ILG induced protonation Ionic-liquid-gating-(ILG-) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the study of a wide range of systems (e.g., SrCoO 2.5 , VO 2 , WO 3 , etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo 2 O 4 , an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo 2 O 4 from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG-induced ionic evolution. Electron Doping

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Metal insulator transition with ferrimagnetic order in epitaxial thin films of spinel NiCo2O4

Cited by 83 publications

References 17 publications

Atomic layer deposition of nickel–cobalt spinel thin films

Atomic layer deposition of nickel–cobalt spinel thin films

Magnetotransport Anomaly in Room‐Temperature Ferrimagnetic NiCo₂O₄ Thin Films

Manipulate the Electronic and Magnetic States in NiCo₂O₄ Films through Electric‐Field‐Induced Protonation at Elevated Temperature

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Metal insulator transition with ferrimagnetic order in epitaxial thin films of spinel NiCo2O4

Cited by 83 publications

References 17 publications

Atomic layer deposition of nickel–cobalt spinel thin films

Atomic layer deposition of nickel–cobalt spinel thin films

Magnetotransport Anomaly in Room‐Temperature Ferrimagnetic NiCo2O4 Thin Films

Manipulate the Electronic and Magnetic States in NiCo2O4 Films through Electric‐Field‐Induced Protonation at Elevated Temperature

Contact Info

Product

Resources

About

Magnetotransport Anomaly in Room‐Temperature Ferrimagnetic NiCo₂O₄ Thin Films

Manipulate the Electronic and Magnetic States in NiCo₂O₄ Films through Electric‐Field‐Induced Protonation at Elevated Temperature