scholarly journals Weak Ferromagnetism in a One-Orbital Double-Exchange Model with Ising Spins for Cerium Oxides

2021 ◽  
Vol 6 (4) ◽  
pp. 53
Author(s):  
Cengiz Şen
Keyword(s):  
Diluted Magnetic Semiconductors ◽  
Magnetic Semiconductors ◽  
Room Temperature Ferromagnetism ◽  
Double Exchange ◽  
Underlying Mechanism ◽  
Exchange Model ◽  
Spin Concentration ◽  
Charge Localization ◽  
Cerium Oxides ◽  
Ising Spins

Cerium oxides (ceria) are materials that exhibit weak, room-temperature ferromagnetism without d-electrons. The latter are usually responsible for magnetism in a variety of other oxide compounds, but the underlying mechanism for such a magnetic response in ceria without the d-electrons (d0-magnetism) is still under debate. A possible explanation is Zener double-exchange, where itinerant electrons polarize the localized spins via Hund-coupling as they hop from site to site. Here, we report magnetization and spin-spin correlation results using various values of the Hund-coupling in a one-orbital double-exchange model with Ising spins. In the real material with formula CeO2−x, the oxygen-deficient sites are denoted by x. These sites are related to the density of tetravalent cerium spins (the Ising spin background in our model), which we denoted as and set at N=0.50 in our simulations. Our results at this value of localized spin concentration show ferromagnetic tendencies at low carrier densities (n=0.25). However, ferromagnetism is lost at intermediate carrier concentrations (n=0.50) due to charge localization at high temperatures, as evident from density of states calculations and Monte Carlo snapshots. To our knowledge, our study based on a realistic Zener-type double exchange mechanism is a first in the study of magnetism in cerium oxides. Our results are also consistent with previous studies using similar Hamiltonians in the context of diluted magnetic semiconductors, where Heisenberg spins were used.

scholarly journals Kinetic Exchange Vs. Room Temperature Ferromagnetism in Diluted Magnetic Semiconductors

2001 ◽  
Vol 690 ◽  
Author(s):  
J. Blinowski ◽  
P. Kacman ◽  
T. Dietl
Keyword(s):  
Diluted Magnetic Semiconductors ◽  
Magnetic Semiconductors ◽  
Room Temperature Ferromagnetism ◽  
Double Exchange ◽  
Internal Reference ◽  
Host Materials ◽  
Magnetic Ions ◽  
Diluted Magnetic ◽  
Shallow Impurities ◽  
P Type

ABSTRACTGuided by the internal-reference rule and the known band o sets in - and - diluted magnetic semiconductors, we discuss the feasibility of obtaining p-type conductivity, required for the carrier-induced ferromagnetism, as well as the cases for which the doping by shallow impurities may lead to the ferromagnetism driven by the double exchange. e consider the dependence of kinetic exchange on the p-d hybridization, on the electronic con gurations of the magnetic ions, and on the energies of the charge transfer betw een the valence band of host materials and the magnetic ions. n the case of n-based - compounds, the doping by acceptors is necessary for the hole-induced ferromagnetism. he latter is, how ever, possible without any doping for some of Mn-, Fe- or Co-based - magnetic semiconductors. n nitrides with Fe or Co carrier-induced ferromagnetism with TC > 300 is expected in the presence of acceptor doping.

Oxide Dilute Magnetic Semiconductors—Fact or Fiction?

MRS Bulletin ◽  
2008 ◽  
Vol 33 (11) ◽  
pp. 1053-1058 ◽  
Author(s):  
J.M.D. Coey ◽  
S.A. Chambers
Keyword(s):  
Thin Films ◽  
High Temperature ◽  
Magnetic Semiconductors ◽  
Bulk Material ◽  
Room Temperature Ferromagnetism ◽  
Magnetic Moments ◽  
Dilute Magnetic Semiconductors ◽  
Double Exchange ◽  
Secondary Phases ◽  
Solid State Mater

AbstractMagnetism in oxides was thought to be well-understood in terms of localized magnetic moments and double-exchange or superexchange rules. This understanding was shaken by the publication of an article in 2001 stating that thin films of anatase TiO2 with only 7 at.% Co substitution had a Curie point in excess of 400 K [Matsumoto et al., Science291, 854 (2001)]. Room-temperature ferromagnetism had previously been predicted for p-type ZnO with 5 at.% Mn [Dietl et al., Science287, 1019 (2000)]. A flood of reports of thin films and nanoparticles of new oxide “dilute magnetic semiconductors” (DMSs) followed, and high-temperature ferromagnetism has been reported for other systems with no 3dcations. The expectation that these materials would find applications in spintronics motivated research in this area. Unfortunately, the data are plagued by instability and a lack of reproducibility. In many cases, the ferromagnetism can be explained by uncontrolled secondary phases; it is absent in well-crystallized films and bulk material. However, it appears that some form of high-temperature ferromagnetism can result from defects present in the oxide films [Coey, Curr. Opin. Solid State Mater. Sci.10, 83 (2007); Chambers, Surf. Sci. Rep.61, 345 (2006)], although they are not DMSs as originally envisaged.

DILUTED MAGNETIC SEMICONDUCTOR NANOWIRES

NANO ◽  
2008 ◽  
Vol 03 (01) ◽  
pp. 1-19 ◽  
Author(s):  
HEON-JIN CHOI ◽  
HAN-KYU SEONG ◽  
UNGKIL KIM
Keyword(s):  
Room Temperature ◽  
Diluted Magnetic Semiconductors ◽  
Magnetic Semiconductors ◽  
Diluted Magnetic Semiconductor ◽  
Room Temperature Ferromagnetism ◽  
Magnetic Semiconductor ◽  
Building Blocks ◽  
Free Standing ◽  
Diluted Magnetic ◽  
Mn Doped

An idea for simultaneously manipulating spin and charge in a single semiconductor medium has resulted in the development of diluted magnetic semiconductors (DMSs), which exhibits surprisingly room temperature ferromagnetic signatures despite having controversial ferromagnetic origin. However, achievement of truly room temperature ferromagnetism by carrier mediation is still the subject of intense research to develop the practical spin-based devices. Nanowires with one-dimensional nanostructure, which offers thermodynamically stable features and typically single crystalline and defect free, have a number of advantages over thin films with respect to studying ferromagnetism in DMSs. This review focuses primarily on our works on GaN -based DMS nanowires, i.e., Mn -doped GaN , Mn -doped AlGaN and Cu -doped GaN nanowires. These DMS nanowires have room temperature ferromagnetism by the local magnetic moment of doping elements that are in a divalent state and in tetrahedral coordination, thus substituting Ga in the wurtzite-type network structure of host materials. Importantly, our evidences indicate that the magnetism is originated from the ferromagnetic interaction driven by the carrier. These outcomes suggest that nanowires are ideal building blocks to address the magnetism in DMS due to their thermodynamic stability, single crystallinity, free of defects and free standing nature from substrate. Nanowires themselves are ideal building blocks for nanodevices and, thus, it would also be helpful in developing DMS-based spin devices.

Annealing Temperature Dependent Ferromagnetic Behaviors Observed in Highly Orientated Pure NiO Thin Films

2014 ◽  
Vol 602-603 ◽  
pp. 956-959
Author(s):  
Yu Jun Zhang ◽  
Yuan Hua Lin ◽  
Ce Wen Nan
Keyword(s):  
Thin Films ◽  
Room Temperature ◽  
Diluted Magnetic Semiconductors ◽  
Annealing Temperature ◽  
Magnetic Semiconductors ◽  
Room Temperature Ferromagnetism ◽  
Film Surface ◽  
Nickel Metal ◽  
Diluted Magnetic ◽  
Ferromagnetic Impurity

Transition metal (TM) doped NiO is a promising candidate of p-type oxide diluted magnetic semiconductors (DMSs), which shows obvious room-temperature ferromagnetism. When researching the magnetic properties of DMSs, it is very important to get rid of ferromagnetic impurity phases by optimizing the preparation process. For this purpose, pure NiO thin films have been deposited by a pulsed laser deposition method and annealed by different annealing process. As-deposited or low-temperature annealed films show room-temperature ferromagnetism and high-temperature annealed films are not ferromagnetic. Nickel metal should be the origin of ferromagnetism in these thin films. On the other hand, high annealing temperature influences the microstructure of the film surface a lot. These results show a useful method to eliminate ferromagnetic impurity in NiO thin films and to optimize the preparation parameters of TM doped NiO thin films.

scholarly journals Room temperature ferromagnetism in metallic Ti1−xVxO2 thin films

RSC Advances ◽  
2018 ◽  
Vol 8 (55) ◽  
pp. 31382-31387 ◽  
Author(s):  
Ze-Ting Zeng ◽  
Feng-Xian Jiang ◽  
Li-Fei Ji ◽  
Hai-Yun Zheng ◽  
Guo-Wei Zhou ◽  
...  
Keyword(s):  
Thin Films ◽  
Transition Metal ◽  
Room Temperature ◽  
Diluted Magnetic Semiconductors ◽  
Magnetic Semiconductors ◽  
Room Temperature Ferromagnetism ◽  
Diluted Magnetic ◽  
Metal Doped

Transition metal doped TiO2 diluted magnetic semiconductors have attracted considerable interest due to their room temperature ferromagnetism.

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