Bound Magnetic Polarons and the Insulator-Metal Transition in EuO

Torrance, J. B.; Shafer, M. W.; McGuire, T. R.

doi:10.1103/physrevlett.29.1168

Cited by 200 publications

(94 citation statements)

References 18 publications

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“…It can be stated that based on experimental results, apparently, it is difficult to give preference to any of the theoretical models I-Mtransition in ferromagnetic ordered state (T<T c ) of EuO 1-δ phase. However, for the paramagnetic (T> T c ) the state of the matrix observed properties monoxide EuO 1-δ in better agreement with the model bound magnetic polaron (H-model Torrance et al [22]). Therefore, it can be assumed that this model is preferred to characterize this transition.…”

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confidence: 51%

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To The Theory of Inverse Transition Insulator-Metal Anion Defective Ferromagnetic Semiconductor Euo<sub>1- δ</sub>

Borukhivich¹,

Troshin²

2017

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Abstract. Based on the available experimental data are made model estimates and the implementation criteria of inverse electron transition insulator-metal set in the "classical" ferromagnetic semiconductor -europium monoxide which is the base model of research in semiconductor spintronics.Keywords: Ferromagnetic semiconductor, europium monoxide, insulator-metal transition, nonstoichiometry, local electronic level, magnetic polaronIn connection with the continued works in recent years the rapid development in the physical materials field of semiconductor spin electronics (spintronics) as a model of research has been and remains a "classic" ferromagnetic semiconductor -europium monoxide -EuO [1]. A characteristic feature of its crystal chemistry is that it is a phase of variable composition, EuO 1+δ , which extends the boundaries of homogeneity in the area of excess (δ<0), and the lack of (δ>0) metal. True nonstehiometric area it is fairly narrow: δ -index varies between 0> δ> 0.005 (excess metal) and 0 <δ <0.035 (excess oxygen).[2] However, depending on the oxygen content significantly are changing the properties monoxide, in particular, the electrical conductivity. At the same time regardless of the sign δ it is always characterized by n-type and its temperature dependence is typical for semiconductors. The specific conductivity values of EuO phase at room temperature are in the range σ = 10 -8 -10 -12 (Ohm•cm) -1 . In the case of excess metal (i.e. anionic defects) samples EuO 1-δ -phase below the Curie temperature (T c = 69.4 K) at the T i ≈ 52 K to test the temperature insulator-metal transition (I -M) with a conductivity jump 13 -15 orders of magnitude [3,4] (Fig.1). A greater jump in the specific electrical resistivity of conductive solid phase is observed only in the superconducting transition in them. In this case, for the phase EuO 1-δ it is the second largest known today jump electrical conductivity in crystals. Moreover, it is the first of the public when it becomes metal the low-temperature ferromagnetic-ordered phase. To date, similar to the character of semiconductor-metal transition, although with a much smaller jump of electric resistivity, Δρ/ρ, is known for some compounds doped of the ferromagnetic ordered lanthanum manganites -the magnetic semiconductors, a value of T c which is capable of more than room temperature [5]. Since the physical nature the I -M-transition in this class of materials has a lot of similarities, we reproduce here the most adopted model previously proposed for europium monoxide and, as we see, there is no other alternative. Illustration of this transition for EuO 1-δ crystals with an index of 0 <δ<0,005 in Fig. 1 also reproduces the effects of an external magnetic field [6].It is evident that the latter shifts the temperature of the electronic transition in the direction of its increase, several reducing the magnitude of the jump ∆ρ/ρ, but without destroying the character of the transition. It should be noted that the insulator-metal transition in a defective oxygen europ...

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supporting

confidence: 51%

“…The author of [18] considered the totality of the data in favor of the transition on Torrance model [22].…”

mentioning

confidence: 99%

To The Theory of Inverse Transition Insulator-Metal Anion Defective Ferromagnetic Semiconductor Euo<sub>1- δ</sub>

Borukhivich¹,

Troshin²

2017

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“…Alternative models based on exchange splitting of the conduction electrons 29 or magnetic polarons, 31 however, predicts a smaller magnetization above 69 K. It suggests a much reduced contribution from the Eu 2+ moments until the temperature is lowered below 69 K. 15,16, 23-25. As shown in Fig. 2 (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Another model based on bound magnetic polaron (BMP) was used to explain the mechanism of oxygen-deficient EuO. 31 An exchange interaction between the doped electrons due to oxygen vacancies and the localized Eu spins was assumed. Whether this exchange coupling is ferromagnetic or antiferromagnetic is still subject to debate.…”

Section: Introductionmentioning

confidence: 99%

Antiferromagnetic coupling in EuO1−x

2012

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The mechanism for the ferromagnetic order in oxygen-deficient europium monoxide EuO 1-x at temperatures higher than 69 K (the Curie temperature Tc of stoichiometric EuO) remains controversial. We have investigated the magnetization of EuO 1-x thin films prepared via pulsed laser deposition as a function of temperature and applied field. The ferromagnetic ordering above 69 K originates from the exchange coupling between the doped electrons and Eu 4f moments and is described using a magnetic polaron model. Our data show that the magnetic polarons are coupled antiferromagnetically to the Eu 4f local moments that dominate the magnetization below 69 K. The magnetic polaron state is stable below 69 K and seems to persist down to a relatively low temperature. An explanation is given to account for the antiferromagnetic coupling. We also describe the evolution of the phases of the magnetic orders as the temperature is varied in EuO 1-x .2

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“…Considering only magnetic interactions, it then oecomes energetically favourable for the electrons to remain localized around the Gd impurities, so as to align their spins with the spins of neighbouring Eu atoms. In such a case, the metallic state is no longer stable with respect to the formation of bound magnetic polarons in an insulating state [6]. Then eqs.…”

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confidence: 99%