| 1. |
- Cedervall, Johan, et al.
(author)
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Magnetocaloric effect in Fe2 P: Magnetic and phonon degrees of freedom
- 2019
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In: Physical Review B. - 2469-9969 .- 2469-9950. ; 99:17
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Journal article (peer-reviewed)abstract
- Devices based on magnetocaloric materials provide great hope for environmentally friendly and energy efficient cooling that does not rely on the use of harmful gasses. Fe2P based compounds are alloys that have shown great potential for magnetocaloric devices. The magnetic behavior in Fe2P is characterized by a strong magnetocaloric effect that coexists with a first-order magnetic transition (FOMT). Neutron diffraction and inelastic scattering, Mossbauer spectroscopy, and first-principles calculations have been used to determine the structural and magnetic state of Fe2P around the FOMT. The results reveal that ferromagnetic moments in the ordered phase are perturbed at the FOMT such that the moments cant away from the principle direction within a small temperature region. The acoustic-phonon modes reveal a temperature-dependent nonzero energy gap in the magnetically ordered phase that falls to zero at the FOMT. The interplay between the FOMT and the phonon energy gap indicates hybridization between magnetic modes strongly affected by spin-orbit coupling and phonon modes leading to magnon-phonon quasiparticles that drive the magnetocaloric effect.
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| 2. |
- Höglin, Viktor, et al.
(author)
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Phase diagram, structures and magnetism of the FeMnP1-xSix-system
- 2015
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In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 5:11, s. 8278-8284
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Journal article (peer-reviewed)abstract
- The magnetic properties of the (Fe,Mn)(2)(P,Si)-system have been shown to be readily manipulated by small changes in composition. This study surveys the FeMnP1-xSix-system (0.00 <= x <= 1.00) reporting sample syntheses and investigations of crystallographic and magnetic properties using X-ray powder diffraction and magnetic measurements. Two single phase regions exist: the orthorhombic Co2P-type structure (x < 0.15) and the Fe2P-type structure (0.24 <= x < 0.50). Certain compositions have potential for use in magnetocaloric applications.
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| 3. |
- Höglin, Viktor, et al.
(author)
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Phase diagram, structures and magnetism of the FeMnP1-xSix-system
- 2015
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In: RSC Advances. - 2046-2069. ; 5:11, s. 8278-8284
-
Journal article (peer-reviewed)abstract
- The magnetic properties of the (Fe,Mn)2(P,Si)-system have been shown to be readily manipulated by small changes in composition. This study surveys the FeMnP1−xSix-system (0.00 ≤ x ≤ 1.00) reporting sample syntheses and investigations of crystallographic and magnetic properties using X-ray powder diffraction and magnetic measurements. Two single phase regions exist: the orthorhombic Co2P-type structure (x < 0.15) and the Fe2P-type structure (0.24 ≤ x < 0.50). Certain compositions have potential for use in magnetocaloric applications.
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| 4. |
- Ivanov, Sergey, et al.
(author)
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Temperature-dependent structural and magnetic properties of R2MMnO6 double perovskites (R=Dy, Gd; M=Ni, Co)
- 2018
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In: Journal of Materials Science: Materials in Electronics. - : Springer Science and Business Media LLC. - 1573-482X .- 0957-4522. ; 29:21, s. 18581-18592
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Journal article (peer-reviewed)abstract
- The structural and magnetic properties of the Dy2CoMnO6, Dy2NiMnO6 and Gd2CoMnO6 double perovskites are investigated using X-ray powder diffraction and squid magnetometry. The materials adopt an orthorhombic structure (space ground Pnma) with disordered Co(Ni)/Mn cations, and exhibit ferrimagnetic transitions near T(C)85, 95, and 115K respectively. T-C was found to monotonously depend on the orthorhombic distortion (a-c)/(a+c) of the compounds. The crystal structure of the compounds was investigated as a function of temperature (16-1100K range), evidencing changes in the BO6 octahedron near T-C. The magnetic entropy changes are estimated for comparison of the magnetocaloric properties to those from literature.
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| 5. |
- Andersson, Mikael Svante, et al.
(author)
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Ageing dynamics of a superspin glass
- 2014
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In: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 108:1, s. 17004-
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Journal article (peer-reviewed)abstract
- Magnetization dynamics of a model superspin glass system consisting of nearly monodispersed close-packed maghemite particles of diameter 8 nm is investigated. The observed non-equilibrium features of the dynamics are qualitatively similar to those of atomic spin glass systems. The intrinsic relaxation function, as observed in zero-field-cooled magnetization relaxation experiments, depends on the time the sample has been kept at constant temperature (ageing). Accompanying low-field experiments show that the archetypal spin glass characteristics -ageing, memory and rejuvenation- are reproduced in this dense system of dipolar-dipolar interacting superspins.
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| 6. |
- Andersson, Mikael Svante, et al.
(author)
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Effects of the individual particle relaxation time on superspin glass dynamics
- 2016
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In: PHYSICAL REVIEW B. - 2469-9950. ; 93:5
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Journal article (peer-reviewed)abstract
- The low temperature dynamic magnetic properties of two dense magnetic nanoparticle assemblies with similar superspin glass transition temperatures T-g similar to 140 K are compared. The two samples are made from batches of 6 and 8 nm monodisperse gamma-Fe2O3 nanoparticles, respectively. The properties of the individual particles are extracted from measurements on reference samples where the particles have been covered with a thick silica coating. The blocking temperatures of these dilute assemblies are found at 12.5 K for the 6 nm particles and at 35 K for the 8 nm particles, which implies different anisotropy energy barriers of the individual particles and vastly different temperature evolution of their relaxation times. The results of the measurements on the concentrated particle assemblies suggest a strong influence of the particle energy barrier on the details of the aging dynamics, memory behavior, and apparent superspin dimensionality of the particles.
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| 7. |
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| 8. |
- Andersson, Mikael Svante, et al.
(author)
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Particle size-dependent superspin glass behavior in random compacts of monodisperse maghemite nanoparticles
- 2016
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In: Materials Research Express. - : IOP Publishing. - 2053-1591. ; 3:4
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Journal article (peer-reviewed)abstract
- Dense random assemblies made from highly monodisperse gamma-Fe2O3 nanoparticles with sizes ranging from 6.2 to 11.5 nm have been investigated by DC and AC magnetometry. It is found that all assemblies undergo superspin glass phase transitions. The superspin glass phase transition temperature is strongly dependent on the particle size and the nature of the interparticle interaction. However the transition from superparamagnet to superspin glass, as evidenced by the shape of the ac-susceptibility curves and the dynamic critical exponents associated with the transition, is similar in all systems.
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| 9. |
- Andersson, Mikael Svante, et al.
(author)
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Size-dependent surface effects in maghemite nanoparticles and its impact on interparticle interactions in dense assemblies
- 2015
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 26:47
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Journal article (peer-reviewed)abstract
- The question of the dominant interparticle magnetic interaction type in random closely packed assemblies of different diameter (6.2-11.5 nm) bare maghemite nanoparticles (NPs) is addressed. Single-particle magnetic properties such as particle anisotropy and exchange bias field are first of all studied in dilute (reference) systems of these same NPs, where interparticle interactions are neglible. Substantial surface spin disorder is revealed in all particles except the smallest, viz. for diameters d = 8-11.5 nm but not for d = 6.2-6.3 nm. X-ray diffraction analysis points to a crystallographic origin of this effect. The study of closely packed assemblies of the d >= 8 nm particles observes collective (superspin) freezing that clearly appears to be governed by interparticle dipole interactions. However, the dense assemblies of the smallest particles exhibit freezing temperatures that are higher than expected from a simple (dipole) extrapolation of the corresponding temperatures found in the d >= 8 nm assemblies. It is suggested that the nature of the dominant interparticle interaction in these smaller particle assemblies is superexchange, whereby the lack of significant surface spin disorder allows this mechanism to become important at the level of interacting superspins.
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| 10. |
- Andersson, Mikael S., et al.
(author)
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Thermally induced magnetic relaxation in square artificial spin ice
- 2016
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
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Journal article (peer-reviewed)abstract
- The properties of natural and artificial assemblies of interacting elements, ranging from Quarks to Galaxies, are at the heart of Physics. The collective response and dynamics of such assemblies are dictated by the intrinsic dynamical properties of the building blocks, the nature of their interactions and topological constraints. Here we report on the relaxation dynamics of the magnetization of artificial assemblies of mesoscopic spins. In our model nano-magnetic system - square artificial spin ice - we are able to control the geometrical arrangement and interaction strength between the magnetically interacting building blocks by means of nano-lithography. Using time resolved magnetometry we show that the relaxation process can be described using the Kohlrausch law and that the extracted temperature dependent relaxation times of the assemblies follow the Vogel-Fulcher law. The results provide insight into the relaxation dynamics of mesoscopic nano-magnetic model systems, with adjustable energy and time scales, and demonstrates that these can serve as an ideal playground for the studies of collective dynamics and relaxations.
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