Long-range magnetic order in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Fe</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>/NiO superlattices

Borchers, J. A.; Erwin, R. W.; Berry, S.; Lind, D. M.; Ankner, John F.; Lochner, Eric; Shaw, Kathryn; Hilton, David K.

doi:10.1103/physrevb.51.8276

Cited by 64 publications

(25 citation statements)

References 32 publications

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“…where m AFM is the magnetization of the Fe in the FeO layer, yields a T N of 800 AE 30 K, a value much larger than the bulk value of 198 K. This large increase of T N is in accordance with the prediction of the mean field theory used to describe the evolution of the magnetic order in ultrathin FM/AFM superlattices [9,16,17]. In the case of a FM/AFM system, the Curie temperature T C of the FM is only weakly dependent on the relative thickness of the FM and AFM layers [17].…”

Section: Prl 103 097201 (2009) P H Y S I C a L R E V I E W L E T T Esupporting

confidence: 77%

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Stabilization of Antiferromagnetic Order in FeO Nanolayers

et al. 2009

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We have studied the evolution of the magnetic state of a nanometer thick antiferromagnetic (AFM) FeO layer during its formation using nuclear resonant scattering of synchrotron radiation. In contact to ferromagnetic Fe, the FeO layer does not show magnetic order at room temperature (RT). Once embedded between two Fe layers, magnetic coupling to the adjacent ferromagnets leads to a drastic increase of the Néel temperature far above RT, while the blocking temperature remains below 30 K. The presented results evidence the role that the ferromagnetic surrounding plays in modifying the magnetic state of ultrathin AFM layers. DOI: 10.1103/PhysRevLett.103.097201 PACS numbers: 75.70.Cn, 75.25.+z, 75.75.+a, 76.80.+y Magnetic data storage technology is reaching the bottom of the nanoscale. The stabilization of magnetic order in low-dimensional structures becomes a key issue. Below a critical thickness, ferromagnets undergo a superparamagnetic relaxation where spins are thermally excited, and the system does not show magnetic hysteresis anymore. Exchange bias bilayer systems composed of a ferromagnet (FM) and an antiferromagnet (AFM) have been recently reported to substantially reduce the critical thickness under which the ferromagnet undergoes superparamagnetic relaxation [1,2]. Layered FM/AFM systems, where an AFM layer (with high anisotropy) is used to pin the magnetization of the FM, are used to create reference magnetic layers in devices. Below a certain temperature (the blocking temperature T B ) the spins in the antiferromagnet are frozen and exchange coupling at the FM/AFM interface leads to a shift of the hysteresis loop and an increase of the coercivity, this phenomenon being known as the exchange bias effect [3,4].In the ultrathin film limit, the thermal stability of these FM/AFM bilayers is strongly modified [5,6]. In exchange bias systems, one usually distinguishes the Néel (ordering) temperature T N of the antiferromagnet and the blocking temperature T B below which exchange bias occurs [7]. For thick AFM layers (> 50 nm), T N and T B are usually found to be equivalent. Field cooling the system below T N directly leads to the freezing of spins (and the appearance of exchange bias). Early studies showed that T B was usually decreasing with decreasing thickness of the AFM layer, and it was assumed that T N was decreasing accordingly due to a finite size effect [5]. Recently, Vallejo-Fernandez et al. found out that the evolution of the exchange bias field H e and T B for polycrystalline films was in fact linked to the average grain volume of the AFM [6], which typically decreases with the layer thickness. This results in a decreased stability against thermal excitation and a decrease of T B . It should be noted that there is still an underlying physics problem as data on epitaxially grown AFM/FM bilayers also show a reduction of T B with a decreasing AFM layer thickness [8,9]; this is still the subject of different theoretical considerations [5,10]. The evolution of T N relative to T B was investigated by Va...

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Section: Prl 103 097201 (2009) P H Y S I C a L R E V I E W L E T T Esupporting

confidence: 77%

“…In the case of a FM/AFM system, the Curie temperature T C of the FM is only weakly dependent on the relative thickness of the FM and AFM layers [17]. In contrast, the T N of the AFM layer is gradually approaching T C when its thickness is reduced.…”

Section: Prl 103 097201 (2009) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 97%

Stabilization of Antiferromagnetic Order in FeO Nanolayers

et al. 2009

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“…23 However, neutron-scattering studies show that the AFM ordering can be stabilized by the presence of an adjacent FM or ferrimagnet. 18,24 Previous measurements on NiO films of similar thickness sandwiched between ͓Co/Pt͔ multilayers 13 indicate that the NiO is AFM ordered well above RT. Following the model of Stiles and McMichael, 25 we envisage the role of the ͓Co/Pt͔ as stabilizing the winding up of domain walls ͑DW͒ in the thin AFM NiO during the Co layer's magnetization reversal.…”

Section: Discussionmentioning

confidence: 99%

Enhanced blocking temperature and isothermal control of hysteresis loop shifts in Co/NiO/[Co/Pt] heterostructures with orthogonal easy axes

Baruth

Adenwalla

2008

Phys. Rev. B

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Heterostructures of Co 4 nm/NiO 1.1 nm/͓Co 0.4 nm/Pt 0.6 nm͔ with mutually orthogonal easy axes allow for isothermal tuning of the hysteresis loop shifts along the applied field axis at room temperature, as well as displaying a greatly enhanced blocking temperature. The loop shifts can be varied up to 35 Oe through the application of moderate dc magnetic fields of 3 kOe. The presence of the ͓Co/Pt͔ multilayer with perpendicular anisotropy is responsible for a significant enhancement of the blocking temperature. For this thickness of NiO, the blocking temperature is expected to be well below 50 K, in contrast to the observed blocking temperature of 225 K. These effects may be tailored by a judicious choice of materials. The dependence of the loop shift on applied field will vary depending on the coercivity and remanance of the ferromagnetic layers. The enhancement of the blocking temperature is highly dependent on the in-plane and out-of-plane anisotropy constants of the intervening antiferromagnet. Both effects are directly relevant to a variety of modern spintronic applications.

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“…14,15,16,17,18,19 There are quite a few works on NiO/Fe 3 O 4 bilayers and multilayers, mostly grown on MgO, investigating the structural properties of the heterostructures and the nature of exchange interaction between magnetite and (the antiferromagnetic) nickel oxide. 13,20,21,22 Thin magnetite films grown on SrTiO 3 (001) allow tuning the conductivity via Nb-doping, which is of interest for some important applications. Quite a few studies reveal altered magnetic properties such as a strongly …”

Section: Introductionmentioning

confidence: 99%