Magnetic characterization of rare-earth oxide nanoparticles...Appl. Phys. Lett. 117, 122410 (2020); doi: 10.1063/5.0023466 117, 122410-2 VC Author(s) 2020 of slow-onset, low-temperature

Appl. Phys. Lett. 117, 122410 (2020); https://doi.org/10.1063/5.0023466 117, 122410

© 2020 Author(s).

Magnetic characterization of rare-earth oxidenanoparticlesCite as: Appl. Phys. Lett. 117, 122410 (2020); https://doi.org/10.1063/5.0023466Submitted: 29 July 2020 . Accepted: 10 September 2020 . Published Online: 23 September 2020

Kai Trepka , and Ye Tao

ARTICLES YOU MAY BE INTERESTED IN

Controlling oxygen distribution of an MgAl2O4 barrier for magnetic tunnel junctions by two-

step processApplied Physics Letters 117, 122409 (2020); https://doi.org/10.1063/5.0015474

Robust spin–orbit torques in ferromagnetic multilayers with weak bulk spin Hall effectApplied Physics Letters 117, 122401 (2020); https://doi.org/10.1063/5.0011399

Magnon-mediated spin currents in Tm3Fe5O12/Pt with perpendicular magnetic anisotropy

Applied Physics Letters 117, 122412 (2020); https://doi.org/10.1063/5.0023242

https://images.scitation.org/redirect.spark?MID=176720&plid=1086294&setID=378288&channelID=0&CID=358612&banID=520068571&PID=0&textadID=0&tc=1&type=tclick&mt=1&hc=bfc173d7818ae60d65aa9b31333cf9d97a846f69&location=https://doi.org/10.1063/5.0023466https://doi.org/10.1063/5.0023466https://aip.scitation.org/author/Trepka%2C+Kaihttps://orcid.org/0000-0002-8672-6317https://aip.scitation.org/author/Tao%2C+Yehttps://doi.org/10.1063/5.0023466https://aip.scitation.org/action/showCitFormats?type=show&doi=10.1063/5.0023466http://crossmark.crossref.org/dialog/?doi=10.1063%2F5.0023466&domain=aip.scitation.org&date_stamp=2020-09-23https://aip.scitation.org/doi/10.1063/5.0015474https://aip.scitation.org/doi/10.1063/5.0015474https://doi.org/10.1063/5.0015474https://aip.scitation.org/doi/10.1063/5.0011399https://doi.org/10.1063/5.0011399https://aip.scitation.org/doi/10.1063/5.0023242https://doi.org/10.1063/5.0023242

Magnetic characterization of rare-earth oxidenanoparticles

Cite as: Appl. Phys. Lett. 117, 122410 (2020); doi: 10.1063/5.0023466Submitted: 29 July 2020 . Accepted: 10 September 2020 .Published Online: 23 September 2020

Kai Trepka1,2 and Ye Tao1,a)

AFFILIATIONS1Rowland Institute at Harvard, 100 Edwin H Land Blvd, Cambridge, Massachusetts 02142, USA2Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St, Cambridge, Massachusetts 02138, USA

a)Author to whom correspondence should be addressed: [email protected]

ABSTRACT

High saturation magnetization and hysteresis-less magnetic responses are desirable for nanoparticles in scientific and technological applica-tions. Rare-earth oxides are potentially promising materials because of their paramagnetism and high magnetic susceptibility in the bulk, butthe magnetic properties of their nanoparticles remain incompletely characterized. Here, we present full M–H loops for commercial RE2O3nanoparticles (RE ¼ Er, Gd, Dy, Ho) with radii from 10–25 nm at room temperature and 4K. The magnetic responses are consistent withtwo distinct populations of atoms, one displaying the ideal Re3þ magnetic moment and the other displaying a sub-ideal magnetic moment. Ifall sub-ideal ions are taken to be on the surface, the data are consistent with � 2� 10 nm surface layers of reduced magnetization. The mag-netization of the rare-earth oxide nanoparticles at low temperatures (1.3–1.9 T) exceeds that of the best iron-based nanoparticles, makingrare-earth oxides candidates for use in next-generation cryogenic magnetic devices that demand a combination of hysteresis-less responseand high magnetization.

VC 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/5.0023466

Paramagnetic nanoparticles (NPs) have revolutionized technol-ogy and everyday life, from targeted drug delivery to geological engi-neering.1–7 For micro- and nanoscale manipulation, particles withhigher magnetization can exert comparatively larger forces necessaryfor sorting of cells and parasites.1–4 In imaging applications such asmagnetic force microscopy and magnetic resonance imaging, highermagnetization enables a higher signal-to-noise ratio and a reducedimaging time.8–10 Rare-earth oxides (RE2O3) have high susceptibility,v, and RE3þ magnetic moment, l,11,12 resulting in high saturationmagnetization, Ms, in the bulk

13 (Table I). However, due to finite-sizeand surface effects, nanoparticles often have altered magneticresponse, including lower Ms compared to bulk materials, makingempirical measurements of rare-earth oxide nanoparticles necessary todetermine their magnetic properties.14–17

In this study, we experimentally investigate the magnetic proper-ties of several RE2O3 nanoparticles to elucidate associated nanoscaleeffects. Magnetic rare-earth oxide nanoparticles—Dy2O3 NP (SSNano,99.9%, 50 nm), Gd2O3 NP (SSNano, 99.9%,

v ¼ CT � h ; (1)

where v is the magnetic susceptibility, C is the Curie constant, T is thetemperature, and h is the Curie temperature. The susceptibilities of thenanoparticles follow Eq. (1) [Fig. 2(a)], with negative Curie tempera-tures h indicative of the emergence of low-temperature antiferromag-netic phases at N�eel temperature TN ¼ �h.18,19 Because of themagnetic transition at TN, the magnetic responses of the materialswere analyzed independently above and below TN. The response of anideal, homogeneous paramagnet to the applied external field is givenby a Langevin function,

M ¼ MsLll0HkBT

� �¼ NlL ll0H

kBT

� �; (2)

whereM represents the sample magnetization,Ms the saturation mag-netization, l the magnetic moment per ion, l0 the vacuum permeabil-ity constant, H the applied field, kB Boltzmann’s constant, T thetemperature, N the density of magnetically active ions, andLðxÞ ¼ cothðxÞ � 1=x.20 We assessed the data against Eq. (2) andfound the model to be insufficient for describing the data. We attributethe difference to various types of heterogeneity that can exist at thenanoscale. Because the nanoparticle size is on the order of a few hun-dred atoms across, nanoparticle properties are often heterogeneous.21

Substantial fractions of each individual particle can belong to distinctsubpopulations, with local heterogeneity in the chemical composition,surface sites, anisotropy, or strain influencing global particle proper-ties.22–25 As a result, we model the nanoparticles as composed of twopopulations of active species, sub-ideal (s), and ideal (i) ions, with thefull response given by a population-weighted sum,

M ¼ N slsLlsl0HkBT

� �þ ð1� sÞliL

lil0HkBT

� �� ; (3)

where s represents the fraction that are sub-ideal ions, ls the averagemoment of sub-ideal ions, and li the moment of each ideal ion, whichwe assume to have the value for the moment of the ideal, bulk RE3þ

ions, i.e., li ¼ lRE3þ . Temperature and field-dependent data collectedabove TN and up to 7T were fitted to this two-component model,resulting in excellent agreement [Figs. 2(b) and 2(c)]. Temperatureand field-dependent data collected below TN and up to 7T were alsofitted to this two-component model [Fig. 2(d)]. Model parameters forboth temperature regimes, including the fraction of sub-ideal/idealions and the magnetic moment of the sub-ideal ions, are reported inTable I. Overall, the nanoparticles display a paramagnetic response,with distinct magnetic populations. The measured remanence of TN regimeMs (T) 1:860:1 1:560:1 2:360:1 2:160:1ls (lB) 2:060:1 0:860:1 5:360:4 0:860:1Sub-ideal fraction s 0:5360:01 0:3760:01 0:6160:04 0:3060:01Thickness t (nm) 1161 461 662 261

Applied Physics Letters ARTICLE scitation.org/journal/apl

Appl. Phys. Lett. 117, 122410 (2020); doi: 10.1063/5.0023466 117, 122410-2

VC Author(s) 2020

https://scitation.org/journal/apl

of slow-onset, low-temperature antiferromagnetic contributions inRE2O3 nanoparticles.

26–29

The magnetic properties of a nanoparticle are often dominatedby surface chemistry,30 with a typically magnetically weaker surface

layer.14,15,31,32 As a result, for T > TN , one possible interpretation isthat the non-ideal ions are ions in the surface layer. Assuming that theglobular nanoparticles (Dy2O3, Ho2O3, and Er2O3) have sphericalmorphology, that the columnar nanoparticles (Gd2O3) have cylindri-cal morphology with length� radius, that all radii are distributed asin Fig. 1(e), and that all non-ideal ions are in the surface layer, thethickness of the surface layer can be computed by numerically solving

1� s ¼Pðri � tÞ3PðR ¼ riÞP

r3i PðR ¼ riÞ; (4)

for the globular nanoparticles and

1� s ¼Pðri � tÞ2PðR ¼ riÞP

r2i PðR ¼ riÞ; (5)

for the columnar nanoparticles, where s is the fraction of atoms in thesurface layer, t is the thickness of the surface layer, ri is the radius of aparticle, and R is the random variable describing the distribution ofparticle radii. Assuming that non-ideal ions are all found in the surfacelayer, the resulting surface layer thicknesses are found and reported(Table I), with values (t ¼ 2� 11 nm) consistent with observations ofmagnetic dead layers in other metal oxide nanostructures (t � 1� 15nm).31,33–35 A future experiment to help determine whether thesub-ideal ions are on the surface or distributed evenly throughout theparticle would sort the particles by size via centrifugation prior tomeasurements to determine whether the surface-area-to-volume ratiocorrelates with s.36

The RE2O3 nanoparticles have high magnetic figures of merit.Linearity of magnetic energy density, Elin, is the energy density that canbe quadratically stored into a material under the drive of an externalfield and captures the sensitivity and linearity of a magnetic material,13

and achievable magnetization is the magnetization at l0H ¼ 7. Idealmagnetic materials for quantitative metrology require both a strongmagnetic response and a long, predictable dynamic range (captured byElin) in order to maximize the signal, minimize the imaging time, andensure undistorted, quantitative results. A review of common and state-of-the-art nanoparticles, thin films, and bulk magnets was per-formed13,37–52 [Fig. 3(a)]. As temperature is decreased, susceptibilityincreases, but the linear range decreases. As a result, optimal particleperformance (maximal Elin) is achieved at cryogenic but non-zero tem-peratures [Fig. 3(b)].13 The rare-earth oxide NPs have high linearities ofmagnetic energy density while exceeding the achievable magnetizationof state-of-the-art iron-based superparamagnetic nanoparticles. As aresult, rare-earth oxide nanoparticles are promising candidates for high-spatial resolution cryogenic magnetic sensing and manipulation.1,4,8–10

In particular, high-Elin, high-magnetization particles may be used inmagnet-on-cantilever tips for cryogenic magnetic force microscopy ormagnetic resonance force microscopy.53–55 Even at room temperature,the particles retain relatively high magnetization and Elin, allowing con-jugation with biologics for use in cell sorting, subcellular characteriza-tion, in vivomagnetic resonance imaging, and drug delivery.56–59

In conclusion, the magnetic properties of rare-earth oxide nano-particles were investigated, with magnetic responses consistent withtwo distinct paramagnetic populations of ions, one with magneticmoment equal to the ideal Re3þ moment and the other with a sub-ideal magnetic moment. If all the sub-ideal ions are taken to be on thesurface of the nanoparticles, the data are consistent with 2–11 nm

FIG. 2. Nanoparticle magnetism. (a) Susceptibility-temperature relationship. The blackline represents a linear fit on the T � 16 K data. (b) Temperature curve of the mag-netic response at l0H ¼ 7 T. (c) M-H loops taken at room temperature. (d) M–H loopstaken at 4 K. In (b)–(d), black lines represent the two-component Langevin fit.



VC Author(s) 2020

https://scitation.org/journal/apl

surface layers of reduced magnetization. The particles display superiorlinearity of magnetic energy density and low-temperature magnetiza-tion exceeding that of state-of-the-art iron-based paramagnetic nano-particles. Looking ahead, the combination of high Ms with a lack ofhysteresis (paramagnetism) suggests that rare-earth oxide nanopar-ticles are likely to advance devices in fields from imaging to magneticmanipulation.

This work was supported by a Rowland Fellowship to Y.T.K.T. acknowledges support from the Rowland Institute and theHarvard Office of Undergraduate Research and Fellowships. Theauthors would like to thank Shaw Huang for assistance withSQUID and all group members for helpful discussions. SEM samplecharacterization studies were carried out at the Center forNanoscale Systems (CNS) at Harvard University.

DATA AVAILABILITY

The data and code that support the findings of this study, includ-ing all SEM data used in the determination of particle morphology for

Fig. 1(e) and the algorithmic outlines for selected particles from Fig. 1,are openly available in GitHub at https://github.com/trepkakai/rare-earth-magnetism, Ref. 60.

REFERENCES1L. Bromberg, E. P. Chang, C. Alvarez-Lorenzo, B. Magari~nos, A. Concheiro,and A. T. Hatton, “Binding of functionalized paramagnetic nanoparticles tobacterial lipopolysaccharides and DNA,” Langmuir 26, 8829–8835 (2010).

2R. Maalouf, W. M. Hassen, C. Fournier-Wirth, J. Coste, and N. Jaffrezic-Renault, “Comparison of two innovatives approaches for bacterial detection:Paramagnetic nanoparticles and self-assembled multilayer processes,”Microchim. Acta 163, 157–161 (2008).

3Z. Heger, N. Cernei, S. Krizkova, M. Masarik, P. Kopel, P. Hodek, O. Zitka, V.Adam, and R. Kizek, “Paramagnetic nanoparticles as a platform for FRET-based sarcosine picomolar detection,” Sci. Rep. 5, 8868 (2015).

4A. H. Schmieder, P. M. Winter, S. D. Caruthers, T. D. Harris, T. A. Williams, J.S. Allen, E. K. Lacy, H. Zhang, M. J. Scott, G. Hu, J. D. Robertson, S. A.Wickline, and G. M. Lanza, “Molecular MR imaging of melanoma angiogenesiswith avb3-targeted paramagnetic nanoparticles,” Magn. Reson. Med. 53,621–627 (2005).

5T. Cyrus, H. Zhang, J. S. Allen, T. A. Williams, G. Hu, S. D. Caruthers, S. A.Wickline, and G. M. Lanza, “Intramural delivery of rapamycin with avb3-targeted paramagnetic nanoparticles inhibits stenosis after balloon injury,”Arter. Thromb. Vasc. Biol. 28, 820–826 (2008).

6S. Laurent, S. Dutz, U. O. H€afeli, and M. Mahmoudi, “Magnetic fluid hyper-thermia: Focus on superparamagnetic iron oxide nanoparticles,” Adv. ColloidInterface Sci. 166, 8–23 (2011).

7S. Ryoo, A. R. Rahmani, K. Y. Yoon, M. Prodanović, C. Kotsmar, T. E. Milner,K. P. Johnston, S. L. Bryant, and C. Huh, “Theoretical and experimental inves-tigation of the motion of multiphase fluids containing paramagnetic nanopar-ticles in porous media,” J. Petrol. Sci. Eng. 81, 129–144 (2012).

8J. G. Longenecker, H. J. Mamin, A. W. Senko, L. Chen, C. T. Rettner, D. Rugar,and J. A. Marohn, “High-gradient nanomagnets on cantilevers for sensitivedetection of nuclear magnetic resonance,” ACS Nano 6, 9637–9645 (2012).

9K. Wago, D. Botkin, C. S. Yannoni, and D. Rugar, “Paramagnetic and ferro-magnetic resonance imaging with a tip-on-cantilever magnetic resonance forcemicroscope,” Appl. Phys. Lett. 72, 2757 (1998).

10U. Hartmann, “Magnetic force microscopy,” Annu. Rev. Mater. Sci. 29, 53–87(1999).

11M. Torii and K. Fukuma, “Absolute calibration of low- and high-field magneticsusceptibilities using rare earth oxides,” Geochem. Geophys. 12, Q07Z28(2011).

12N. Greenwood and A. A. Earnshaw, Chemistry of the Elements (Elsevier, 2012).13K. Trepka, R. Hauert, C. Cancellieri, and Y. Tao, “A robust metal oxide thinfilm with cryogenic saturation magnetization exceeding 2 Tesla,” Matter 3,1–12 (2020).

14G. C. Papaefthymiou, “Nanoparticle magnetism,” Nano Today 4, 438–447 (2009).15E. Morosan, A. Fleitman, Q. Huang, J. W. Lynn, Y. Chen, X. Ke, M. L.Dahlberg, P. Schiffer, C. R. Craley, and R. J. Cava, “Structure and magneticproperties of the Ho2Ge2O7 pyrogermanate,” Phys. Rev. B 77, 224423 (2008).

16T. N. Shendruk, R. D. Desautels, B. W. Southern, and J. van Lierop, “The effectof surface spin disorder on the magnetism of c-Fe2O3 nanoparticle dis-persions,” Nanotechnology 18, 455704 (2007).

17A. Punnouse, H. Magnone, M. S. Seehra, and J. Bonevich, “Bulk to nanoscalemagnetism and exchange bias in CuO nanoparticles,” Phys. Rev. B 64, 174420(2001).

18Z. Heiba and M. B. Mohamed, “Structural and magnetic properties of Mndoped Ho2O3 nanocrystalline,” J. Mol. Struct 1102, 135–140 (2015).

19N. Spaldin, Magnetic Materials: Fundamentals and Applications (CambridgeUniversity Press, 2010).

20Y. Nakatani, Y. Uesaka, N. Hayashi, and H. Fukushima, “Computer simulationof thermal fluctuation of fine particle magnetization based on Langevin equa-tion,” J. Magn. Magn. Mater. 168, 347–351 (1997).

21I. Khaan, S. Khalid, and I. Khan, “Nanoparticles: Properties, applications andtoxicities,” Arab. J. Chem. 12, 908–931 (2019).

FIG. 3. Figure of Merit. (a) The RE2O3 NPs (bolded labels, filled circles) have supe-rior linearity of magnetic energy density and approach the experimentally achiev-able magnetization (M at l0H ¼ 7 T) of strong ferromagnets such as iron anddysprosium. Circles represent measurements of thin films or nanostructures, whilediamonds represent measurements of bulk materials. Materials are color-coded: Dy(green), Gd (orange), Ho (blue), Er (red), La (purple), and all other materials(black). (b) Temperature dependencce of linearity of magnetic energy density, withcomputation as described in previous work.13



VC Author(s) 2020

https://github.com/trepkakai/rare-earth-magnetismhttps://github.com/trepkakai/rare-earth-magnetismhttps://doi.org/10.1021/la904589phttps://doi.org/10.1007/s00604-008-0008-3https://doi.org/10.1038/srep08868https://doi.org/10.1002/mrm.20391https://doi.org/10.1161/ATVBAHA.107.156281https://doi.org/10.1016/j.cis.2011.04.003https://doi.org/10.1016/j.cis.2011.04.003https://doi.org/10.1016/j.petrol.2011.11.008https://doi.org/10.1021/nn3030628https://doi.org/10.1063/1.121081https://doi.org/10.1146/annurev.matsci.29.1.53https://doi.org/10.1029/2011GC003694https://doi.org/10.1016/j.matt.2020.07.031https://doi.org/10.1016/j.nantod.2009.08.006https://doi.org/10.1103/PhysRevB.77.224423https://doi.org/10.1088/0957-4484/18/45/455704https://doi.org/10.1103/PhysRevB.64.174420https://doi.org/10.1016/j.molstruc.2015.08.048https://doi.org/10.1016/S0304-8853(96)00725-1https://doi.org/10.1016/j.arabjc.2017.05.011https://scitation.org/journal/apl

22J.-M. Rabanel, V. Adibnia, S. Tehrani, S. Sanche, P. Hildgen, X. Banquy, and C.Ramassamy, “Nanoparticle heterogeneity: An emerging structural parameterinfluencing particle fate in biological media?,” Nanoscale 11, 383–406 (2019).

23J. Sambur and P. Chen, “Approaches to single-nanoparticle catalysis,” Annu.Rev. Phys. Chem. 65, 395–422 (2014).

24A. Ugulava, S. Chkhaidze, S. Kekutia, and Z. Rostomashvili, “Magnetization ofsuperparamagnetics in the state of mechanical anisotropy,” arXiv:1512.07751(2015).

25C. Johnson, E. Snoeck, M. Ezcurdia, B. Rodr�ıguez-Gonz�alez, I. Pastoriza-Santos, L. Liz-Marz�an, and M. H�ytch, “Effects of elastic anisotropy on straindistributions in decahedral gold nanoparticles,” Nat. Mater. 7, 120–124 (2008).

26V. Narang, D. Korakakis, and M. S. Seehra, “Nature of magnetism and mag-netic-field-induced transitions in non-collinear antiferromagnet Er2O3,”J. Magn. Magn. Mater. 368, 353–359 (2014).

27K. P. Shinde, V. M. Tien, L. Huang, H. R. Park, S. C. Yu, K. C. Chung, and D.H. Kim, “Magnetocaloric effect in Tb2O3 and Dy2O3 nanoparticles at cryogenictemperatures,” J. Appl. Phys. 127, 054903 (2020).

28A. Boutahar, S. Bahhar, H. Lemziouka, R. Moubah, E. K. Hlil, E. Lorenzo, andH. Lassri, “Mn doping effects on the structural, magnetic and magnetocaloricproperties in Ho2O3 powders,” J. Magn. Magn. Mater. 504, 166684 (2020).

29E. L. Correa1, B. Bosch-Santos, F. H. M. Cavalcante, B. S. Correa, R. S. Freitas,A. W. Carbonari1, and M. P. A. Potiens, “Properties of Gd2O3 nanoparticlesstudied by hyperfine interactions and magnetization measurements,” AIP Adv.6, 056112 (2016).

30E. Tronc, D. Fiorani, M. Noguès, F. Testa, A. M. ad Lucari, F. D’Orazio, J. M.Grenèche, W. Wernsdorfer, N. Galvez, C. Chen�eac, D. Mailly, and J. P. Jolivet,“Surface effects in noninteracting and interacting c-Fe2O3 nanoparticles,”J. Magn. Magn. Mater. 262, 6–14 (2003).

31S. S. P. Parkin, R. Sigsbee, R. Felici, and G. P. Felcher, “Observation of magneticdead layers at the surface of iron oxide films,” Appl. Phys. Lett. 48, 604 (1986).

32J. Salafranca, J. Gazquez, N. Perez, A. Labarta, S. Pantelides, S. Pennycook, X.Batlle, and M. Varela, “Surfactant organic molecules restore magnetism inmetal-oxide nanoparticle surfaces,” Nano Lett. 12, 2499–2503 (2012).

33S. Y. Jang, C. Y. You, S. H. Lim, and S. R. Lee, “Annealing effects on the mag-netic dead layer and saturation magnetization in unit structures relevant to asynthetic ferrimagnetic free structure,” J. Appl. Phys. 109, 013901 (2011).

34N. Mottaghi, M. S. Seehra, R. Trappen, S. Kumari, C. Huang, S. Yousefi, G. B.Cabrera1, A. H. Romero1, and M. B. Holcomb, “Insights into the magneticdead layer in La0.7Sr0.3MnO3 thin films from temperature, magnetic field andthickness dependence of their magnetization,” AIP Adv. 8, 056319 (2018).

35R. P. Borges, W. Guichard, J. G. Lunney, J. M. D. Coey, and F. Ott, “Magneticand electric “dead” layers in (La0.7Sr0.3)MnO3 thin films,” J. Appl. Phys. 89,3868 (2001).

36O. Akbulut, C. R. Mace, R. V. Martinez, A. A. Kumar, Z. Nie, M. R. Patton,and G. M. Whitesides, “Separation of nanoparticles in aqueous multiphase sys-tems through centrifugation,” Nano Lett. 12, 4060–4064 (2012).

37H. J. Mamin, C. T. Rettner, M. H. Sherwood, L. Gao, and D. Rugar, “Highfield-gradient dysprosium tips for magnetic resonance force microscopy,”Appl. Phys. Lett. 100, 013102 (2012).

38D. Zhang, J. Zhu, N. Zhang, T. Liu, L. Chen, X. Liu, R. Ma, H. Zhang, and G.Qiu, “Controllable fabrication and magnetic properties of double-shell cobaltoxides hollow particles,” Sci. Rep. 5, 8737 (2015).

39A. Naveen and S. Selladurai, “Tailoring structural, optical and magnetic prop-erties of spinel type cobalt oxide (Co3O4) by manganese doping,” Physica BCondens. Matter 457, 251–262 (2015).

40A. Tamm, J. Kozlova, L. Aarik, J. Aarik, K. Kukli, J. Link, and R. Stern,“Dysprosium oxide and dysprosium-oxide-doped titanium oxide thin filmsgrown by atomic layer deposition,” J. Vac. Sci. Technol., A 33, 01A127 (2015).

41H. Deng, X. Li, Q. Peng, X. Wang, J. Chen, and Y. Li, “Monodisperse magneticsingle-crystal ferrite microspheres,” Angew. Chem., Int. Ed. 44, 2782–2785(2005).

42K. Woo, J. Hong, S. Choi, H.-W. Lee, J.-P. Ahn, C. S. Kim, and S. W. Lee,“Easy synthesis and magnetic properties of iron oxide nanoparticles,” Chem.Mater. 16, 2814–2818 (2004).

43C. Martinez-Boubeta, K. Simeonidis, A. Makridis, M. Angelakeris, O. Iglesias,P. Guardia, A. Cabot, L. Yedra, S. Estrad�e, F. Peir�o, Z. Saghi, P. A. Midgley, I.Conde-Lebor�an, D. Serantes, and D. Baldomir, “Learning from nature toimprove the heat generation of iron-oxide nanoparticles for magnetic hyper-thermia applications,” Sci. Rep. 3, 1652 (2013).

44S. J. Kemp, R. M. Ferguson, A. P. Khandar, and K. M. Krishnan,“Monodisperse magnetite nanoparticles with nearly ideal saturation magnet-ization,” RSC Adv. 6, 77452–77464 (2016).

45K. Chahara, T. Ohno, M. Kasai, and Y. Kozono, “Magnetoresistance in mag-netic manganese oxide with intrinsic antiferromagnetic spin structure,” Appl.Phys. Lett. 63, 1990–1992 (1993).

46S. Thota, B. Prasad, and J. Kumar, “Formation and magnetic behaviourof manganese oxide nanoparticles,” Mater. Sci. Eng., B 167, 153–160(2010).

47J. Shin, R. Anisur, M. K. Ko, G. H. Im, J. H. Lee, and I. S. Lee, “Hollow manga-nese oxide nanoparticles as multifunctional agents for magnetic resonanceimaging and drug delivery,” Angew. Chem., Int. Ed. 48, 321–324 (2009).

48P. Mele, C. Artini, A. Ubaldini, G. A. Costa, M. M. Carnasciali, and R. Masini,“Synthesis, structure and magnetic properties in the Nd2O3-Gd2O3 mixed sys-tem synthesized at 1200

�C,” J. Phys. Chem. Solids 70, 276–280 (2009).

49X. Wei, R. Skomski, B. Balamurugan, Z. G. Sun, S. Ducharme, and D. J.Sellmyer, “Magnetism of TiO and TiO2 nanoclusters,” J. Appl. Phys. 105,07C517 (2009).

50K. Kukli, M. Kemell, M. C. Dimri, E. Puukilainen, A. Tamm, R. Stern, M.Ritala, and M. Leskel€a, “Holmium titanium oxide thin films grown by atomiclayer deposition,” Thin Solid Films 565, 261–266 (2014).

51H. I. Lee, S. W. Lee, C. K. Rhee, and Y. Sohn, “Paramagnetic Ho2O3 nanowires,nano-square sheets, and nanoplates,” Ceram. Int. 44, 17919–17924 (2018).

52J. Crangle and G. M. Goodman, “The magnetization of pure iron and nickel,”Proc. Roy. Soc. Lond. A 321, 477–491 (1971).

53D. Rugar, R. Budakian, H. J. Mamin, and B. W. Chui, “Single spin detection bymagnetic resonance force microscopy,” Nature 430, 329–332 (2004).

54Y. Tao and C. Degen, “Growth of magnetic nanowires along freely selecta-blehkl crystal directions,” Nat. Commun. 9, 339 (2018).

55Y. Pan, C. Miller, K. Trepka, and Y. Tao, “Wafer-scale photolithography ofultra-sensitive nanocantilever force sensors,” Appl. Phys. Lett. 113, 083103(2018).

56R. D. Corato, N. C. Bigall, A. Ragusa, D. Dorfs, A. Genovese, R. Marotta, L.Manna, and T. Pellegrino, “Multifunctional nanobeads based on quantum dotsand magnetic nanoparticles: Synthesis and cancer cell targeting and sorting,”ACS Nano 5, 1109–1121 (2011).

57M. Labib, Z. Wang, S. U. Ahmed, R. M. Mohamadi, B. Duong, B. Green, E. H.Sargent, and S. O. Kelley, “Tracking the expression of therapeutic protein tar-gets in rare cells by antibody-mediated nanoparticle labelling and magneticsorting,” Nat. Biomed. Eng. (published online).

58C. Bouzigues, T. Gacoin, and A. Alexandrou, “Biological applications of rare-earth based nanoparticles,” ACS Nano 5, 8488–8505 (2011).

59C. Li and J. Lin, “Rare earth fluoride nano-/microcrystals: Synthesis, surfacemodification and application,” J. Mater. Chem 20, 6831–6847 (2010).

60K. Trepka, “Rare earth magnetism data,” Zenodo (2020). http://doi.org/10.5281/zenodo.4031414



VC Author(s) 2020

https://doi.org/10.1039/C8NR04916Ehttps://doi.org/10.1146/annurev-physchem-040513-103729https://doi.org/10.1146/annurev-physchem-040513-103729http://arxiv.org/abs/1512.07751https://doi.org/10.1038/nmat2083https://doi.org/10.1016/j.jmmm.2014.05.026https://doi.org/10.1063/1.5120350https://doi.org/10.1016/j.jmmm.2020.166684https://doi.org/10.1063/1.4943601https://doi.org/10.1016/S0304-8853(03)00011-8https://doi.org/10.1063/1.96481https://doi.org/10.1021/nl300665zhttps://doi.org/10.1063/1.3527968https://doi.org/10.1063/1.5005913https://doi.org/10.1063/1.1331658https://doi.org/10.1021/nl301452xhttps://doi.org/10.1063/1.3673910https://doi.org/10.1038/srep08737https://doi.org/10.1016/j.physb.2014.10.024https://doi.org/10.1016/j.physb.2014.10.024https://doi.org/10.1116/1.4902079https://doi.org/10.1002/anie.200462551https://doi.org/10.1021/cm049552xhttps://doi.org/10.1021/cm049552xhttps://doi.org/10.1038/srep01652https://doi.org/10.1039/C6RA12072Ehttps://doi.org/10.1063/1.110624https://doi.org/10.1063/1.110624https://doi.org/10.1016/j.mseb.2010.01.049https://doi.org/10.1002/anie.200802323https://doi.org/10.1016/j.jpcs.2008.10.010https://doi.org/10.1063/1.3074509https://doi.org/10.1016/j.tsf.2014.06.028https://doi.org/10.1016/j.ceramint.2018.06.267https://doi.org/10.1098/rspa.1971.0044https://doi.org/10.1038/nature02658https://doi.org/10.1038/s41467-017-02519-8https://doi.org/10.1063/1.5043479https://doi.org/10.1021/nn102761thttps://doi.org/10.1038/s41551-020-0590-1https://doi.org/10.1021/nn202378bhttps://doi.org/10.1039/c0jm00031khttp://doi.org/10.5281/zenodo.4031414https://scitation.org/journal/apl

d1d2d3f1t1d4d5f2lc1c2c3c4c5c6c7c8c9c10c11c12c13c14c15c16c17c18c19c20c21f3c22c23c24c25c26c27c28c29c30c31c32c33c34c35c36c37c38c39c40c41c42c43c44c45c46c47c48c49c50c51c52c53c54c55c56c57c58c59c60

Documents

Magnetic characterization of rare-earth oxide nanoparticles...Appl. Phys. Lett. 117, 122410 (2020); doi: 10.1063/5.0023466 117, 122410-2 VC Author(s) 2020 of slow-onset, low-temperature