Despite the advances in the methods for fabricating nanoscale materials, critical issues remain, such as the difficulties encountered in anchoring, and the deterioration in their stability after integration with other components. These issues need to be addressed to further increase the scope of their applicability. In this study, using epitaxial mesoscopic host matrices, materials are spatially confined at the nanoscale, and are supported, anchored, and stabilized. They also exhibit properties distinct from the bulk counterparts proving their high quality nanoscale nature. ZnFe2O4and SrTiO3are used as the model confined material and host matrix, respectively. The ZnFe2O4phases are spatially confined by the SrTiO3mesoscopic matrix and have strongly enhanced ferrimagnetic properties as compared to bulk and plain thin films of ZnFe2O4, with a Curie temperature of ≈500 K. The results of a series of control experiments and characterization measurements indicate that cationic inversion, which originates from the high interface‐to‐volume ratio of the ZnFe2O4phase in the ZnFe2O4–SrTiO3nanocomposite film, is responsible for the magnetization enhancement. An exchange bias is observed, owing to the coexistence of ferrimagnetic and antiferromagnetic regions in the confined ZnFe2O4phase. The magnetic properties are dependent on the ZnFe2O4crystallite size, which can be controlled by the growth conditions.
Magnetic Properties of Proton Irradiated Mn3Si2Te6 van der Waals Single Crystals
The bulk van der Waals crystal Mn3Si2Te6 (MST) has been irradiated with a proton beam of 2 MeV at a fluence of 1×1018 H+ cm-2. The temperature dependent magnetization measurements show a drastic decrease in the magnetization of 49.2% in the H//c direction observed in ferrimagnetic state. This decrease in magnetization is also reflected in the isothermal magnetization curves. No significant change in the ferrimagnetic transition temperature (75 K) was reflected after irradiation. Electron paramagnetic resonance (EPR) spectroscopy shows no magnetically active defects present after irradiation. Here, experimental findings gathered from MST bulk crystals via magnetic measurements, magnetocaloric effect, and heat capacity are discussed.
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- Award ID(s):
- 1855377
- NSF-PAR ID:
- 10113331
- Date Published:
- Journal Name:
- MRS Advances
- ISSN:
- 2059-8521
- Page Range / eLocation ID:
- 1 to 8
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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van der Waals (vdW) magnetic materials show promise in being the foundation for future spintronic technology. The magnetic behavior of Fe2.7GeTe2 (FGT), a vdW itinerant ferromagnet, was investigated before and after proton irradiation. Proton irradiation of the sample was carried out at a fluence of 1×1018 cm-2. The magnetization measurements revealed a small increase of saturation magnetization (Ms) of about 4% upon proton irradiation of the sample, in which, the magnetic field was applied parallel to the c-axis. X-ray photoelectron spectroscopy for pristine and irradiated FGT revealed a general decrease in intensity after irradiation for Ge and Te and an increase in peak intensity of unavoidable surface iron oxide. Furthermore, no noticeable change in the Curie temperature (TC =152 K) is observed in temperature dependent magnetization variation. This work signifies the importance of employing protons in tuning the magnetic properties of vdW materials.more » « less
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SUMMARY Lamellar magnetism is a source of remanent magnetization in natural rocks different from common bulk magnetic moments in ferrimagnetic minerals. It has been found to be a source for a wide class of magnetic anomalies with extremely high Koenigsberger ratio. Its physical origin are uncompensated interface moments in contact layers of nanoscale ilmenite lamellae inside an hematite host, which also generate unusual low-temperature (low-T) magnetic properties, such as shifted low-T hysteresis loops due to exchange bias. The atomic-magnetic basis for the exchange bias discovered in the hematite-ilmenite system is explored in a series of papers. In this third article of the series, simple models are developed for lamellae interactions of different structures when samples are either cooled in zero-field, or field-cooled in 5 T to temperatures below the ordering temperature of ilmenite. These models are built on the low-temperature measurements described earlier in Paper II. The important observations include: (i) the effects of lamellar shapes on magnetic coupling, (ii) the high-T acquisition of lamellar magnetism and low-T acquisition of magnetization of ilmenite lamellae, (iii) the intensity of lamellar magnetism and the consequent ilmenite magnetism in populations of randomly oriented crystals, (iv) lattice-preferred orientation of the titanohematite host crystal populations and (v) the effects of magnetic domain walls in the host on hysteresis properties. Based on exemplary growth models of lamellae with different geometries and surface couplings we here provide simple models to assess and explain the different observations listed above. Already the simplified models show that the shapes of the edges of ilmenite lamellae against their hematite hosts can control the degree of low-T coupling between ilmenite, and the lamellar magnetic moments. The models also explain certain features of the low-T exchange bias in the natural samples and emphasize the role of lattice-preferred orientation upon the intensity of remanent magnetization. The inverse link between ilmenite remanence and exchange-bias shift in bimodal low-T ilmenite lamellae is related to different densities of hematite domain walls induced by the clusters of ilmenite lamellae.more » « less
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Amorphous magnetic alloys with large perpendicular magnetic anisotropy (PMA) have emerged as a suitable material choice for spintronic memory and high-frequency non-reciprocal devices on-chip. Unlike ferromagnets, ferrimagnets offer faster switching dynamics, lower net saturation magnetization, minimal stray field and a lower net angular momentum. Ferrimagnetic thin films of Gd x Co 1− x sputter deposited as heterostructures of Ta/Pt/Gd x Co 1− x (t)/Pt on Si/SiO 2 have bulk-like PMA for thicknesses of 5–12 nm and room-temperature magnetic compensation for x = 28–32%. Preferential oxygenation of GdCo has been found to increase the effective anisotropy energy density by an order of magnitude and produce near-ideal remanence ratios. X-ray photoelectron spectroscopy accurately quantifies the metal-oxidation ratio, which shows that an oxygen-rich and Co-deficient stoichiometry (Gd 21 Co 28 O 51 ) likely weakens the ferromagnetic exchange interaction between Co–Co and contributes additional antiferromagnetic exchange through superexchange-like interactions between Gd and Co via O, resulting in a stronger out-of-plane magnetization. Even greater PMA and giant-anisotropy field of 11 kOe are achieved in super-lattices of the Gd 21 Co 28 O 51 heterostructure. The combination of ferrimagnetic ordering in amorphous Gd x Co 1− x and its affordance of pathways for engineering large PMA will enable the design of integrated high-frequency devices beyond 30 GHz and ultrafast energy efficient memory devices with switching speeds down to tens of picoseconds.more » « less
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Abstract Using light irradiation to manipulate magnetization over a prolonged period of time offers a wealth of opportunities for spin‐based electronics and photonics. To date, persistent photomagnetism has been frequently reported in spin systems composed of molecular magnets; yet this phenomenon is rarely observed in nanoparticle‐based systems comprised of transition metal oxides. Here, detailed studies of persistent photomagnetism in superparamagnetic iron oxide (Fe3O4) nanoparticles at temperatures below their blocking temperature are presented and it is demonstrated that the magnetization change does not occur through steady‐state spin transitions or photothermal heating. Instead, it is found that exciton–spin exchange‐coupling plays a critical role in modulating the magnetization by lowering the anisotropic energy barrier of Fe3O4nanoparticles to facilitate their optically driven conversion from ferrimagnetic to superparamagnetic. Collectively, these insights establish a comprehensive understanding of the underlying photophysical processes that regulate photomagnetism in nanoparticle‐based magnetic systems composed of transition metal oxides.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1557/adv.2019.260
