Electrical Transport Properties of the Insulating Ferromagnetic Spinels CdCr2S4 and CdCr2Se4

Lehmann, Hauke; Robbins, M.

doi:10.1063/1.1708485

Cited by 93 publications

(37 citation statements)

References 7 publications

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“…The semiconducting behavior from applying a small DC current is also consistent with LSDA+U calculation 13 and the earlier electrical transport measurements. 15 However, with an increase in the applied current, an astonishing feature appears near T C . A clear metal-insulator transition (MIT) near T C was observed in CdCr 2 S 4 , mimicking the electric transport property of CMR manganites.…”

Section: 12mentioning

confidence: 99%

Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr2S4

Sun

Huang

Lin

et al. 2010

Applied Physics Letters

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Colossal magnetoresistance (CMR) and electroresistance (CER) induced by the electric field in spinel multiferroic CdCr 2 S 4 are reported. It is found that a metal-insulator transition (MIT) in CdCr 2 S 4 is triggered by the electrical field. In magnetic fields, the resistivity  of CdCr 2 S 4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr 2 S 4 the unique compound to possess all four properties of the colossal magnetocapacitive (CMC), colossal electrocapacitive (CEC), CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.

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Section: 12mentioning

confidence: 99%

Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr2S4

Sun

Huang

Lin

et al. 2010

Applied Physics Letters

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“…As an alternative explanation of the MC effect one could consider a magnetic-field induced variation of charge-carrier mobility or density. A s izable dc magnetoresistance effect is well known for CdCr 2 S 4 [8], but it cannot be responsible for the observed anomalies of ε', the dc resistivity only contributing to ε". In contrast, hoppingtype charge transport is known to give rise to ac conductivity, approximated by the U DR, which via the Kramers-Kronig relation leads to ε' ~ ν s-1 [ 6].…”

mentioning

confidence: 99%

Relaxation dynamics and colossal magnetocapacitive effect inCdCr2S4

et al. 2005

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A thorough investigation of the relaxational dynamics in the recently discovered multiferroic CdCr 2 S 4 showing a colossal magnetocapacitive effect has been performed. Broadband dielectric measurements without and with external magnetic fields up to 10 T provide clear evidence that the observed magnetocapacitive effect stems from enormous changes of the relaxation dynamics induced by the development of magnetic order.PACS numbers: 75.80.+q, 77.22.Gm Multiferroic materials, showing the simultaneous occurrence of dielectric and magnetic order, are a "hot" topic in recent solid state research [1,2]. Especially the strong variation of electric (magnetic) properties under application of a magnetic (electric) field found in some of these materials, make them highly attractive not only from an academic point of view, but also for potential applications in microelectronics. Among the recently discovered multiferroics, the spinel compound CdCr 2 S 4 is exceptional, showing ferromagnetic and relaxor ferroelectric behavior with sizable ordering temperatures and, most remarkably, a colossal magnetocapacitive (MC) effect of nearly 500% in an external magnetic field H = 5 T [2]. However, so far the origin of the strong MC coupling in this compound is unknown. In [2], it was suggested that it may arise from the magnetic field affecting the relaxor dynamics of the polar moments, but alternatively also effects resulting from the hopping dynamics of localized charge carriers were discussed. In the present letter, from broadband dielectric measurements, we provide detailed information on the relaxation dynamics in CdCr 2 S 4 , both in the paramagnetic and ferromagnetic state. The results clearly reveal that it is the radical change of the relaxational dynamics driven by the magnetization that leads to the observed colossal MC effects in this compound.For the present investigation, CdCr 2 S 4 single crystals of the same batch as in [2] were used, with sputtered goldcontacts being applied on opposite sides of the plate-like samples. Dielectric constant and loss were measured over a broad frequency range of 12 decades (3 mHz < ν < 3 GHz) using frequency-response analysis and a reflectometric technique [3]. A conventional 4 He bath-cryostat and a cryomagnet allowed measurements at temperatures down to

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“…On the other hand, a contribution from hoppingtype charge transport to the anomaly at T c via a variation of the ac conductivity, affecting also ε', cannot be excluded, especially as it is well known that CdCr 2 S 4 exhibits sizeable magneto-resistance effects 15 . In any case, overall the magneto-capacitive coupling in CdCr 2 S 4 is different to all mechanisms observed so far and purely dynamic in origin.…”

mentioning

confidence: 99%

“…Ferromagnetism in CdCr 2 S 4 is well known 10 , but early experimental observations of a number of mysterious features have fallen into oblivion: For example, reports of an anomalous expansion coefficient at low temperatures 11,12 , an unexpected concomitant broadening of the d iffraction lines 11 , a strong blue shift of the absorption edge on passing the ferromagnetic phase transition 13 , the observation of anomalously large phonon shifts and damping effects close to T c 14 and the observation of large magneto-resistance effects 15 . Figure 1a shows the inverse magnetic susceptibility χ -1 and the low-temperature magnetization M. The straight line indicates a fit to the paramagnetic susceptibility, which results in a Curie-Weiss temperature of 155 K and a paramagnetic moment of 3.88 µ B , close to the theoretically expected value of 3.87 µ B per Cr…”

mentioning

confidence: 99%

Relaxor ferroelectricity and colossal magnetocapacitive coupling in ferromagnetic CdCr2S4

Hemberger¹,

Lunkenheimer²,

Fichtl³

et al. 2005

Nature

500

317

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, which reveal magnetic and electric order, are in the focus of recent solid state research [1][2][3][4] . Especially the simultaneous occurrence of ferroelectricity and ferromagnetism, combined with an intimate coupling of magnetization and polarization via magneto-capacitive effects, could pave the way for a new generation of electronic devices. Here we present measurements on a simple cubic spinel with unusual properties: It shows ferromagnetic order and simultaneously relaxor ferroelectricity, i.e. a ferroelectric cluster state, reached by a smeared-out phase transition, both with sizable ordering temperatures and moments. Close to the ferromagnetic ordering temperature the magneto-capacitive coupling, characterized by a variation of the dielectric constant in an external magnetic field, reaches colossal values of nearly 500%. We attribute the relaxor properties to geometric frustration, which is well known for magnetic moments, but here is found to impede long-range order of the structural degrees of freedom.The coexistence of ferroelectricity and ferromagnetism would constitute a mile stone for modern electronics and functionalised materials. The most appealing applications are new types of storage media using both magnetic and electric polarization and the possibility of electrically reading/writing magnetic memory devices (and vice versa). However, it is clear now that ferroelectric ferromagnets are rare 5,6 and mostly exhibit rather weak ferromagnetism. Spinel compounds are an important class of materials and their electronic properties are in the focus of research since the famous work of Verwey on magnetite 7 . Recent reports on geometrical frustration of the spin and orbital degrees of freedom 8 , and the observation of an orbital-glass state 9 in sulpho spinels, demonstrate the rich and complex physics, characteristic of these compounds. Here we report on another interesting experimental observation in a spinel system: R elaxor ferroelectricity in ferromagnetic CdCr 2 S 4 and the occurrence of colossal magnetocapacitive effects.CdCr 2 S 4 crystallizes in the normal cubic spinel structure (space group Fd3m, a = 1.024 nm), with Cr 3+ octahedrally surrounded by sulphur ions, yielding a half-filled lower t 2g triplet with a spin S = 3/2. Ferromagnetism in CdCr 2 S 4 is well known 10 , but early experimental observations of a number of mysterious features have fallen into oblivion: For example, reports of an anomalous expansion coefficient at low temperatures 11,12 , an unexpected concomitant broadening of the d iffraction lines 11 , a strong blue shift of the absorption edge on passing the ferromagnetic phase transition 13 , the observation of anomalously large phonon shifts and damping effects close to T c 14 and the observation of large magneto-resistance effects 15 . Figure 1a shows the inverse magnetic susceptibility χ -1 and the low-temperature magnetization M. The straight line indicates a fit to the paramagnetic susceptibility, which results in a Curie-Weiss temperature of 155 K and a paramagneti...

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Electrical Transport Properties of the Insulating Ferromagnetic Spinels CdCr2S4 and CdCr2Se4

Cited by 93 publications

References 7 publications

Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr2S4

Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr2S4

Relaxation dynamics and colossal magnetocapacitive effect inCdCr2S4

Relaxor ferroelectricity and colossal magnetocapacitive coupling in ferromagnetic CdCr2S4

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