Exchange bias and spin glass behavior in biphasic NiFe2O4/NiO thin films

Pebley, Andrew C.; Fuks, Preston; Pollock, Tresa M.; Gordon, Michael J.

doi:10.1016/j.jmmm.2016.06.009

“…Table 1 provides our values of HE and coercivity enhancement together with the literature ones for Ni-based thin films at 4-10 K. In a recent work, A. C. Pebley et al presented nanogranular NiFe2O4/NiO with a large shift of hysteresis loop at 5 K of about 2 kOe due to structural disorders in the ferrimagnet/antiferromagnet interfaces [45]. Systems with ferromagnet/antiferromagnet interfaces [41][42][43][44]46,47] (see Table 1) show relatively small HE down to 100 Oe compared to our NiCo/NiCoO multilayer.…”

Section: Magnetic Characterizationmentioning

confidence: 94%

Magnetic Aspects and Large Exchange Bias of Ni0.9Co0.1/NiCoO Multilayers

Anyfantis

¹

,

Kanistras

²

,

Ballani

³

et al. 2021

Micro

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Ultrathin films of Ni0.9Co0.1 were grown by radio frequency magnetron sputtering. By means of a periodic natural oxidation procedure they were transformed into Ni0.9Co0.1/NiCoO multilayers. Room temperature hysteresis loops recorded via the magneto-optic Kerr effect have revealed over all in-plane magnetic anisotropy due to magnetostatic anisotropy. Mild thermal annealing at 250 °C enhanced a tendency for perpendicular magnetic anisotropy, mainly due to an increase of the uniaxial volume anisotropy term. Spin reorientation transition, exchange bias larger than 700 Oe, and strong coercivity enhancement were observed via a superconducting quantum interference device at low temperatures after field cooling.

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“…coercivity H C , remanence M R and loop-shift or exchange bias H EB for the ZFC and FC samples, provides a useful way to determine the nature of magnetic phases present in a sample. Particularly noteworthy is the result that H EB is expected only if an AFM phase combined with another phase (ferromagnetic, ferrimagnetic, SG or uncompensated spins) are present [56][57][58][59][60]. For these measurements of the hysteresis loops and the associated loop parameters, the sample was cooled from the PM phase to the measuring temperature in H = 0 for the ZFC or H = 90 kOe for the FC case.…”

Section: Hysteresis Loops Exchange Bias and Their Temperature Dependencementioning

confidence: 99%

Antiferromagnetism, spin-glass state, H–T phase diagram, and inverse magnetocaloric effect in Co₂RuO₄

Ghosh

¹

,

Joshi

²

,

Pramanik

³

et al. 2020

J. Phys.: Condens. Matter

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Static and dynamic magnetic properties of normal spinel Co2RuO4 = (Co2+) are reported based on our investigations of the temperature (T), magnetic field (H) and frequency (f) dependence of the ac-magnetic susceptibilities and dc-magnetization (M) covering the temperature range T = 2 K–400 K and H up to 90 kOe. These investigations show that Co2RuO4 exhibits an antiferromagnetic (AFM) transition at TN ∼ 15.2 K, along with a spin-glass state at slightly lower temperature (TSG) near 14.2 K. It is argued that TN is mainly governed by the ordering of the spins of Co2+ ions occupying the A-site, whereas the exchange interaction between the Co2+ ions on the A-site and randomly distributed Ru3+ on the B-site triggers the spin-glass phase, Co3+ ions on the B-site being in the low-spin non-magnetic state. Analysis of measurements of M (H, T) for T < TN are used to construct the H–T phase diagram showing that TSG shifts to lower T varying as H2/3.2 expected for spin-glass state whereas TN is nearly H-independent. For T > TN, analysis of the paramagnetic susceptibility (χ) vs. T data are fit to the modified Curie–Weiss law, χ = χ0 + C/(T + θ), with χ0 = 0.0015 emu mol−1Oe−1 yielding θ = 53 K and C = 2.16 emu-K mol−1Oe−1, the later yielding an effective magnetic moment μeff = 4.16 μB comparable to the expected value of μeff = 4.24 μB per Co2RuO4. Using TN, θ and high temperature series for χ, dominant exchange constant J1/kB ∼ 6 K between the Co2+ on the A-sites is estimated. Analysis of the ac magnetic susceptibilities near TSG yields the dynamical critical exponent zν = 5.2 and microscopic spin relaxation time τ0 ∼ 1.16 × 10−10 sec characteristic of cluster spin-glasses and the observed time-dependence of M(t) is supportive of the spin-glass state. Large M–H loop asymmetry at low temperatures with giant exchange bias effect (HEB ∼ 1.8 kOe) and coercivity (HC ∼ 7 kOe) for a field cooled sample further support the mixed magnetic phase nature of this interesting spinel. The negative magnetocaloric effect observed below TN is interpreted to be due to the AFM and SG ordering. It is argued that the observed change from positive MCE (magnetocaloric effect) for T > TN to inverse MCE for T < TN observed in Co2RuO4 (and reported previously in other systems also) is related to the change in sign of (∂M/∂T) vs. T data.

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“…In the recent years, there is upsurge in the research on inverse spinel cobalt titanate (Co 2 TiO 4 ) due to its unique catalytical activity and magnetic features such as negative magnetization, magnetic compensation, polarity reversal Negative magnetization and the exchange bias have drawn the attention of the scientific community due to their potential applications in magnetic read/write heads, switching devices, magnetic random-access memory devices, spin-valves and various other spintronic devices [10][11][12][13][14][15][16][17]. Generally, the asymmetry in the magnetization versus magnetic field loops (also popularly known as exchange-bias field, H EB ) is a key feature noticeable in the compounds like Co 2 Ti(Sn, Ru)O 4 , (NiCo) 1−x Zn x Fe 2 O 4 , CoFe 2 O 4 and CoCr 2 O 4 and many more complex spinel oxides due to the couplings at the interface between the antiferromagnetic (AFM) phase and other magnetic phases such as ferromagnetic (FM), ferrimagnetic (FiM), or spin-glass (SG) [18][19][20][21][22][23][24]. In this paper we present ab initio calculations on the Ge substituted Co 2 TiO 4 (Co 2 Ti 1−x Ge x O 4 ) and investigate the changes in electronic and magnetic properties as the structure is tuned from inverse FiM spinel (Co 2 TiO 4 ) to normal pyrochlore AFM spinel (GeCo 2 O 4 ).…”

Section: Introductionmentioning

confidence: 99%

Tailoring the electronic structure and magnetic properties of pyrochlore Co₂Ti_1−xGe_xO₄: a GGA + U ab initio study

Ghosh¹,

Singh²,

Das³

et al. 2021

J. Phys.: Condens. Matter

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We report the electronic structure and magnetic properties of Co2Ti1−x Ge x O4 (0 ⩽ x ⩽ 1) spinel by means of the first-principle methods of density functional theory involving generalized gradient approximation along with the on-site Coulomb interaction (U eff) in the exchange-correlation energy functional. Special emphasis has been given to explore the site occupancy of Ge atoms in the spinel lattice by introducing the cationic disorder parameter (y) which is done in such a way that one can tailor the pyrochlore geometry and determine the electronic/magnetic structure quantitatively. For all the compositions (x), the system exhibits weak tetragonal distortion (c/a ≠ 1) due to the non-degenerate d z 2 and d x 2 − y 2 states (e g orbitals) of the B-site Co. We observe large exchange splitting (ΔEX ∼ 9 eV) between the up and down spin bands of t 2g and e g states, respectively, of tetrahedral and octahedral Co2+ (4A2(g)(F)) and moderate crystal-field splitting (ΔCF ∼ 4 eV) and the Jahn–Teller distortion (ΔJT ∼ 0.9 eV). These features indicate the strong intra-atomic interaction which is also responsible for the alteration of energy band-gap (1.7 eV ⩽ E g ⩽ 3.3 eV). The exchange interaction (J BB ∼ −4.8 meV, for (x, y) = (0.25, 0)) between the Co2+ dominates the overall antiferromagnetic behaviour of the system for all ‘x’ as compared to J AA (∼−2.2 meV, for (x, y) = (0.25, 0)) and J AB (∼−1.8 meV, for (x, y) = (0.25, 0)). For all the compositions without any disorderness in the system, the net ferrimagnetic moment (Δμ) remains constant, however, increases progressively with increasing x due to the imbalance of Co spins between the A- and B-sites.

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Exchange bias and spin glass behavior in biphasic NiFe2O4/NiO thin films

Cited by 17 publications

References 50 publications

Magnetic Aspects and Large Exchange Bias of Ni0.9Co0.1/NiCoO Multilayers

Magnetic Aspects and Large Exchange Bias of Ni0.9Co0.1/NiCoO Multilayers

Antiferromagnetism, spin-glass state, H–T phase diagram, and inverse magnetocaloric effect in Co₂RuO₄

Tailoring the electronic structure and magnetic properties of pyrochlore Co₂Ti_1−xGe_xO₄: a GGA + U ab initio study

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Exchange bias and spin glass behavior in biphasic NiFe2O4/NiO thin films

Cited by 17 publications

References 50 publications

Magnetic Aspects and Large Exchange Bias of Ni0.9Co0.1/NiCoO Multilayers

Magnetic Aspects and Large Exchange Bias of Ni0.9Co0.1/NiCoO Multilayers

Antiferromagnetism, spin-glass state, H–T phase diagram, and inverse magnetocaloric effect in Co2RuO4

Tailoring the electronic structure and magnetic properties of pyrochlore Co2Ti1−x Ge x O4: a GGA + U ab initio study

Contact Info

Product

Resources

About

Antiferromagnetism, spin-glass state, H–T phase diagram, and inverse magnetocaloric effect in Co₂RuO₄

Tailoring the electronic structure and magnetic properties of pyrochlore Co₂Ti_1−xGe_xO₄: a GGA + U ab initio study