On the ferromagnetic ground state of SmN

McNulty, James; Ruck, B. J.; Trodahl, H. J.

doi:10.1103/physrevb.93.054413

Cited by 36 publications

(22 citation statements)

References 47 publications

(93 reference statements)

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“…However, there are limited examples for solids with native (“undiluted”) semiconductor ferromagnetism. Only little attention was devoted to semiconductor ferromagnets such as GdN, SmN, EuO, or EuS in the past . When it comes to bulk materials, Europium(II) oxide is the most studied.…”

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confidence: 99%

Nanomorphology Effects in Semiconductors with Native Ferromagnetism: Hierarchical Europium (II) Oxide Tubes Prepared via a Topotactic Nanostructure Transition

et al. 2017

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Semiconductors with native ferromagnetism barely exist and defined nanostructures are almost unknown. This lack impedes the exploration of a new class of materials characterized by a direct combination of effects on the electronic system caused by quantum confinement effects with magnetism. A good example is EuO for which currently no reliable routes for nanoparticle synthesis can be established. Bottom‐up approaches applicable to other oxides fail because of the labile oxidation state +II. Instead of targeting a direct synthesis, the two steps—“structure control” and “chemical transformation”—are separated. The generation of a transitional, hybrid nanophase is followed by its conversion into EuO under full conservation of all morphological features. Hierarchical EuO materials are now accessible in the shape of oriented nanodisks stacked to tubular particles. Magnetically, the coupling of either vortex or onion states has been found. An unexpected temperature dependence is governed by thermally activated transitions between these states.

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mentioning

confidence: 99%

Nanomorphology Effects in Semiconductors with Native Ferromagnetism: Hierarchical Europium (II) Oxide Tubes Prepared via a Topotactic Nanostructure Transition

et al. 2017

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“…however the existence of carrier mediated ferromagnetism remains an open question [56]. Several of the ground state magnetic moments are also in disagreement with theoretical Hund's rule free-ion values [57,58]. Undoubtedly as the experimental picture becomes clearer, this will aid theoretical studies and methods to understand the rich magnetic properties offered by the RENs.…”

Section: Magnetic Properties Of Rare-earth Nitridesmentioning

confidence: 99%

“…Hund's rules are based on empirical observations of the electron interactions and magnetic moments of free ions. They are useful for qualitative analysis, however in general other effects in solids such as the crystal field must be taken into account 4 [57]. The first two rules arise from the Pauli exclusion principle and Coulomb repulsion, and the third is a result of the effects of spin-orbit coupling.…”

Section: Hund's Rules and Magnetismmentioning

confidence: 99%

Device Applications of Rare-Earth Nitrides

Warring¹

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<p>In this thesis the properties of thin film spintronic devices are investigated. These devices incorporate rare-earth nitrides as the active elements in a geometry with vertical transport perpendicular to the layers. Many rare-earth nitrides are ferromagnetic semiconductors with a rich range of magnetic properties arising from their 4-f magnetic moments. These magnetic moments contain both spin and orbital contributions, in contrast to the quenched, spin-based magnetism frequently exploited in spintronic devices based on transition metals. Magnetic tunnel junctions are demonstrated with the ferromagnetic electrodes made from the intrinsic ferromagnetic semiconductor GdN surrounding GaN and AlN barriers. Fitting of the current-voltage characteristics of a GdN/GaN/GdN device determines a barrier height of 1.5 eV at room temperature. This puts the GdN Fermi level close to the GaN mid-gap, consistent with recent theoretical predictions of the band alignment at the GdN/GaN interface [Kagawa et al., Phys. Rev. Applied 2, 054009 (2014)]. This barrier height is found to scale with the band gap of the group-III nitride barrier, being approximately twice as large for AlN barriers. It was observed that the barrier height reduces as the AlN barrier thickness increases, signalling the formation of Schottky barriers at the interface. These polycrystalline junctions exhibit a tunnel magnetoresistance of a few percent but do not show clear signs of homogeneous switching. The transport properties of the GdN/GaN/GdN junctions are heavily influenced by the electronic structure of the semiconducting GdN layers, making junctions based on rare-earth nitrides promising candidates for further investigation. A fully semiconductor-based magnetic tunnel junction that uses spin-orbit coupled materials made of intrinsic ferromagnetic semiconductors is then presented. Unlike more common approaches, one of the electrodes consists of a near-zero magnetic moment ferromagnetic semiconductor, samarium nitride, with the other electrode comprised of the more conventional ferromagnetic semiconductor gadolinium nitride. Fabricated tunnel junctions exhibit magnetoresistances as high as 200%, implying strong spin polarisation in both electrodes. In contrast to conventional tunnel junctions, the resistance is largest at high fields, a direct result of the orbital-dominant magnetisation in samarium nitride that requires the spin in this electrode aligns opposite to that in the gadolinium nitride when the magnetisation is saturated. The magnetoresistance at intermediate fields is controlled by the formation of a twisted magnetisation phase in the samarium nitride, a direct result of the orbital-dominant ferromagnetism. Thus, new functionality can be brought to magnetic tunnel junctions by use of novel electrode materials, in contrast to the usual focus on tuning the barrier properties. Finally, highly resistive GdN films intentionally doped with Mg are demonstrated. These films are found to have increased resistivities and decreased carrier concentrations, with no observed degradation in crystal quality as compared with undoped films. An increase of the Curie temperature in conductive films is observed which is consistent with the existence of magnetic polarons centred on nitrogen vacancies. The prospect of doping rare-earth nitride films in this manner promises greater control of the material properties and future device applications.</p>

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“…The early research reported the Neel temperature 𝑇 𝑁 was 13 K [118], 15 K [119], or 18.2 K [120]. The antiferromagnetic nature of this material was rejected later once the subsequent measurements of both neutron scattering [121] and recent XMCD studies [122,123] very clearly showed the ferromagnetic nature with a small magnetic moment.…”

Section: Magnetic and Electronic Properties Of Samarium Nitridementioning

confidence: 99%

Investigation of the electron and thermal transport in rare-earth nitrides

Maity¹

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<p>Gadolinium nitride (GdN) and samarium nitride (SmN) have been widely studied to understand their ferromagnetic ordering and electronic structure, and for their promise in spintronics applications. This thesis presents experimental magnetotransport studies of GdN and SmN films in which experimental results have been compared with the existing band structure calculation. Three GdN films have been prepared in different conditions, among them two films are epitaxial quality and one film is polycrystalline in nature, and two films of SmN were also studied. Their magnetic properties were probed by SQUID magnetometry and they are found to be ferromagnetic. The transition temperature differs from sample to sample and this behaviour has been attributed to the presence of magnetic polarons that nucleate around nitrogen vacancies and give rise to an inhomogeneous ferromagnetic state. The charge transport results have been discussed for all GdN and SmN films. A full set of charge/heat transport results are obtained on only one epitaxial GdN. The difference of resistivity among these samples is noticeable. The Hall effect results show the presence of different carrier concentration with at most only weak temperature dependence. We also have noticed the presence of anomalous Hall effect in the paramagnetic region for a lower-concentration epitaxial GdN. The thermopower in both GdN and SmN was measured to provide further insight into the material’s electronic properties. In this thesis we present the first experimental investigation of the thermopower of epitaxial gadolinium nitride and samarium nitride films, measured using an experimental set-up designed for measuring the temperature dependent thermopower of thin films. Our result shows a negative thermopower for both GdN and SmN films and simple, though strong temperature dependence. At low temperatures we observe a peak near the ferromagnetic transition temperature in GdN. The results are interpreted in terms of the diffusion thermopower. Overall the results suggest that the nitrogen vacancy concentration controls the carrier concentration and plays a significant role towards the transport properties. We conclude that all films are either heavily, moderately or weakly doped semiconductors with a metallic characteristic.</p>

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On the ferromagnetic ground state of SmN

Cited by 36 publications

References 47 publications

Nanomorphology Effects in Semiconductors with Native Ferromagnetism: Hierarchical Europium (II) Oxide Tubes Prepared via a Topotactic Nanostructure Transition

Nanomorphology Effects in Semiconductors with Native Ferromagnetism: Hierarchical Europium (II) Oxide Tubes Prepared via a Topotactic Nanostructure Transition

Device Applications of Rare-Earth Nitrides

Investigation of the electron and thermal transport in rare-earth nitrides

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