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At least 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Control of spin dynamics in artificial honeycomb spin-ice-based nanodisks

In this paper, we report the experimental and theoretical characterization of the angular-dependent spin dynamics in arrays of ferromagnetic nanodisks arranged on a honeycomb lattice. The magnetic field and microwave frequency dependence, measured by broadband ferromagnetic resonance, reveal a rich spectrum of modes that is strongly affected by the microstate of the network. Based on symmetry arguments with respect to the external field, we show that certain parts of the ferromagnetic network contribute to the detected signal. A comparison of the experimental data with micromagnetic simulations reveals that different subsections of the lattice predominantly contribute to the high-frequency response of the array. This is confirmed by optical characterizations using microfocused Brillouin light scattering. Furthermore, we find indications that nucleation and annihilation of vortexlike magnetization configurations in the low-field range affect the dynamics, which is different from clusters of ferromagnetic nanoellipses. Our work opens up new perspectives for designing magnonic devices that combine geometric frustration in gyrotropic vortex crystals at low frequencies with magnonic crystals at high frequencies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Magnetic anisotropy in uranium monosulfide probed by magnetic torque measurements

We have studied the magnetic torque in uranium monosulfide (US) single crystals to explore the magnetic anisotropy in this material. Uranium monosulfide crystallizes in a cubic, NaCl-type of crystal structure and exhibits the largest magnetocrystalline anisotropy observed in cubic systems. By performing detailed torque measurements we observe a strongly anisotropic behavior in the paramagnetic phase due to crystal defects and quadrupolar pair interactions. Our studies also confirm the presence of a large anisotropy in the ferromagnetic state of the US system with the <100>, <111>, and <110> directions being the hard, easy, and intermediate axes, respectively. Furthermore, the anisotropy in the paramagnetic phase shows similar characteristics to the anisotropy observed in the ferromagnetic phase, as characterized by second and fourth rank susceptibility terms. The similarity of the anisotropic behaviors in paramagnetic and ferromagnetic phases is the consequence of strong magnetoelastic properties in this system, which possibly lead to the rhombohedral structural distortion, not only in the ferromagnetic phase but also in the paramagnetic phase (induced by applied magnetic field).

36 MATERIALS SCIENCE↗
DOE OSTI2024

Inhomogeneous magnetic ordered state and evolution of magnetic fluctuations in Sr⁢(Co 1–x ⁢Ni x ) 2 ⁢P 2 revealed by 31 P NMR

SrCo 2 ⁢P 2 with a tetragonal structure is known to be a Stoner-enhanced Pauli paramagnetic metal being nearly ferromagnetic. Recently J. Schmidt et al. [Phys. Rev. B 108, 174415 (2023)] reported that a ferromagnetic ordered state is actually induced by a small Ni substitution for Co of x = 0.02 in Sr⁢(Co 1–x ⁢Ni x ) 2 ⁢P 2 where an antiferromagnetic ordered phase also appears by further Ni substitution with x = 0.06–0.35. Here, in this work, using nuclear magnetic resonance (NMR) measurements on 31 P nuclei, we have investigated how the magnetic properties change by the Ni substitution in Sr⁢(Co 1–x ⁢Ni x ) 2 ⁢P 2 from a microscopic point of view, especially focusing on the evolution of magnetic fluctuations with the Ni substitution and the characterization of the magnetically ordered states. The temperature dependencies of the 31 P spin-lattice relaxation rate divided by temperature (1/T 1 ⁢T) and Knight shift (K) for SrCo 2 ⁢P 2 are reasonably explained by a model where a double-peak structure for the density of states near the Fermi energy is assumed. Based on a Korringa ratio analysis using the T 1 and K data, ferromagnetic spin fluctuations are found to dominate in the ferromagnetic Sr⁢(Co 1–x ⁢Ni x ) 2 ⁢P 2 as well as the antiferromagnets where no clear antiferromagnetic fluctuations are observed. We also found the distribution of the ordered Co moments in the magnetically ordered states from the analysis of the 31 P-NMR spectra exhibiting a characteristic rectangular-like shape.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Role of the Cluster Structure of Amorphous Fe{sub 67}Cr{sub 18}B{sub 15} Alloy in Magnetism and in the Changing of Electron Scattering Mechanisms under the Influence of Ion (Ar{sup +}) Irradiation

The contribution of clusters of different sizes to magnetism and the switching of electron scattering mechanisms in amorphous Fe{sub 67}Cr{sub 18}B{sub 15} alloy during ion Ar{sup +} irradiation is studied. The cluster magnetism is found to be related to the presence of clusters of the following two types: large α-(Fe, Cr) clusters of size D = 150–250 Å and small (D = 40–80 Å) clusters in a random intercluster medium. The generation of small ferromagnetic and antiferromagnetic clusters during ion irradiation leads to the formation of cluster glass, which affects the electrical properties of the alloy and causes a magnetic frustration. The temperature dependence of the barrier height is shown to characterize the magnetic state of the alloy in low fields. On the whole, the temperature dependence of the order parameter is a universal characteristic of the system. The temperature dependence of resistivity of initial alloys in the temperature range 98–300 K (ρ(T) ∝ T{sup 2}) is determined by electron scattering by quantum defects, and the transition into a ferromagnetic state is revealed when the derivative ∂ρ/∂T ∝ T is analyzed. The increase in resistivity and the relation ρ ∝ T{sup 1/2} in strongly inhomogeneous samples after irradiation at a dose Φ = 1.5 × 10{sup 18} ions/cm{sup 2} are caused by weak localization effects, and the transition to a ferromagnetic state becomes obvious when the derivative ∂ρ/∂T ∝ T{sup –1/2} is considered. Irradiation by fluence Φ = 3 × 10{sup 18} ions/cm2 induces a giant (twofold) increase in the alloy density, restores the ferromagnetism of large clusters, decreases the resistivity by 37%, and restores the relation ρ(T) ∝ T{sup 2}, which results from the overlapping of the irradiation-induced small clusters when their concentration increases and from an increase in the alloy density. The overlapping of clusters lowers the barrier height and decreases the sensitivity of the alloy to an applied field. The relation ρ(T) ∝ T{sup 2} is valid for the entire temperature range T = 2–300 K because of the partial screening of the magnetic moments of large clusters by a medium having the properties of cluster glass.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Effect of Cr Spacer on Structural and Magnetic Properties of Fe/Gd Multilayers

Here, we analyze the role of a thin Cr spacer between Fe and Gd layers on the structure and magnetic properties of a [Fe(35 Å)/Cr(t Cr )/Gd(50 Å)/Cr(t Cr )] 12 superlattice. Samples without the Cr spacer (t Cr = 0) and with a thin spacer (t Cr = 4 Å) are investigated using X-ray diffraction, polarized neutron and resonance X-ray magnetic reflectometry, static magnetometry, magneto-optical Kerr effect, and ferromagnetic resonance techniques. Magnetic properties are studied experimentally in a wide temperature range 4–300 K and analyzed theoretically using numerical simulation on the basis of the mean-field model. We show that a reasonable agreement with the experimental data can be obtained considering temperature dependence of the effective field parameter in gadolinium layers. In conclusion, the analysis of the experimental data shows that besides a strong reduction of the antiferromagnetic coupling between Fe and Gd, the introduction of Cr spacers into Fe/Gd superlattice leads to modification of both structural and magnetic characteristics of the ferromagnetic layers.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Spatially Resolved Large Magnetization in Ultrathin BiFeO 3

Complex interactions across the interface in heterostructures can generate novel functionalities not present in the constituent materials. Here, we create a unique ferromagnetic ground state out of normally antiferromagnetic BiFeO 3 (BFO) by interleaving it with layers of ferromagnetic La 0.7 Sr 0.3 MnO 3 . Intriguingly, we found that the magnetization of BFO was aligned opposite to that of the manganite layers. Based on polarized neutron reflectometry (PNR) depth profiling of custom-designed layers, we obtained a net magnetization in the BFO layers of 275 kA/m (~1.83 B/Fe) at 10 K, which is two times larger than the previously reported values. Additionally, ferromagnetic order in the BFO persists up to 200 K, which is much higher than previously seen in BFO heterostructures. Our unprecedented understanding of the evolution of magnetism and functional coupling across the interface between antiferromagnetic and ferromagnetic layers provides a blueprint towards advanced spintronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Nonvolatile Electric Control of the Anomalous Hall Effect in an Ultrathin Magnetic Metal

Abstract Low‐dimensional magnetism has been boosted by the recent discovery of the ferromagnetism in layered two‐dimensional (2D) semiconductors. Although the macroscopic magnetic moments of 2D ferromagnets are weak, the anomalous Hall effect (AHE) can serve as a versatile electric probe to their magnetic properties. Here, the nonvolatile electric‐field manipulation of the AHE in an ultrathin metallic ferromagnet with perpendicular magnetic anisotropy at room temperature is reported, which is achieved by the electrostatic modulation of the longitudinal resistivity via a ferroelectric substrate without varying magnetization. Therefore, this work demonstrates an electric‐field‐controlled room‐temperature memory device based on the zero‐magnetic‐field anomalous Hall resistance of an ultrathin ferromagnet. More importantly, the experimental results disentangle magnetization and anomalous Hall resistance. As a result, the study reveals a linear decrease of anomalous Hall conductivity with normal conductivity, which is distinct from previous scaling relations. Accordingly, this work manifests a universe avenue to harnessing the AHE in low‐dimensional magnetic materials.

Feng, Zexin↗
DOE OSTI2018

Electronic, Magnetic and Optical Properties of TM (Ti, V, Cr, Mn and Co)-Doped Rare-Earth Nitride GdN: First-Principles Theory

The half-metallic ferromagnetic behavior of rare-earth nitride Gd{sub 0.95} TM{sub 0.05}N (TM = Ti, V, Cr, Mn and Co), based on diluted magnetic semiconductors (DMSs), is investigated using the Korringa–Kohn–Rostoker (KKR) method combined with the coherent potential approximation (CPA) within a framework of density functional theory (DFT). The energy difference between the ferromagnetic and disorder local moment states has been evaluated. The exchange interactions obtained from first-principles calculations resulted in ferromagnetic states with Curie temperatures within the ambient conditions. Moreover, the optical absorption spectra obtained by ab initio calculations confirm the ferromagnetic stability based on the charge state of magnetic impurities.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Comprehensive study of the magnetic phase transitions in Tb 3 Co combining thermal, magnetic and neutron diffraction measurements

A comprehensive study of the magnetic phase transitions in Tb 3 Co has been undertaken combining different techniques. Using single crystal neutron diffraction in the paramagnetic state a weak crystal structure distortion from the room temperature orthorhombic structure of the Fe 3 C type described with the Pnma space group toward structure with lower symmetry has been observed with cooling below 100 K. At 81 K there is a second order phase transition to an antiferromagnetic incommensurate phase with the propagation vector k = (0.155, 0, 0). As derived from thermal diffusivity measurements, the critical exponents for this transition are very close to the 3D-Heisenberg universality class, proving that the magnetic interactions are short-range but with a deviation from perfect isotropy due to crystal field effects. At T 2 ≈ 70 K there is another magnetic phase transition to a ferromagnetic state whose character is shown to be weakly first order. The low temperature magnetic state has a non-coplanar ferromagnetic structure with strong ferromagnetic components of Tb magnetic moments along the crystallographic c-axis. The application of an external magnetic field B = 2 T along the crystallographic c-axis suppresses the incommensurate antiferromagnetic phase and gives rise to the ferromagnetic phase. The magnetic entropy peak change as well as the refrigerant capacity indicate that Tb 3 Co is a competitive magnetocaloric material in this temperature range.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Electronic structure and magnetism of pristine, defected, and strained $\mathrm{Ti_2N}$ $\mathrm{MX}$ene

Here, from first principles electronic structure calculations, we unravel the evolution of structural, electronic, and magnetic properties of pristine, defected, and strained titanium nitride MXene with different functional groups (-F, -O, -H, and -OH). The formation and cohesive energies reveal their chemical stability. The dynamical stability of Ti 2 N mono-layer is also confirmed by phonon calculations. The MAX phase and defect free functionalized MXenes are metallic except for oxygen terminated (Ti 2 NO 2 ) one which is 100% spin polarized half-metallic ferromagnet. The spin–orbit coupling significantly influences the bare MXene (Ti 2 N) to exhibit Dirac topology and band inversion near the high symmetry directions. The strain effect sways the Fermi level thereby shifting it towards lower energy state under compression and towards higher energy state under tensile strain in Ti 2 NH 2 . The Ti 2 NO 2 exhibits exotic electronic structure not only in pristine but also in strained and defected structures. Its half-metallic nature changes to semi-metallic under 1% compression and it is completely destroyed under 2% compression. In single vacancy defect, its band structure remarkably transforms from half-metallic to semi-conducting with large band gap in 12.5% Ti, weakly semi-conducting in 5.5% Ti, and semi-metallic in 12.5% O. The 25% N defect changes its half-metallic characteristic to metallic. Further, the 12.5% Co substitution preserves its half-metallic character, whereas Mn substitution allows it to convert half-metallic characteristic into weak semi-metallic characteristic preserving ferromagnetism. However, Cr substitution converts half-metallic ferromagnetic state to half-metallic anti-ferromagnetic state. The understanding made here on collective structural stability, and electronic band structure, and magnetic phenomena in novel 2D Ti 2 N derived MXenes open up their possibility in designing them for synthesis.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Confinement of quasi-atomic structures in Ti 2 N and Ti 3 N 2 MXene electrides

Metal carbides, nitrides, or carbonitrides of early transition metals, better known as MXenes, possess notable structural, electrical, and magnetic properties. Analyzing electronic structures by calculating structural stability, band structure, density of states, Bader charge transfer, and work functions utilizing first principle calculations, we revealed that titanium nitride MXenes, namely Ti 2 N and Ti 3 N 2 , have excess anionic electrons in their lattice voids, making them MXene electrides. Bulk Ti 3 N 2 has competing antiferromagnetic (AFM) and ferromagnetic (FM) configurations with slightly more stable AFM configuration, while the Ti 2 N MXene is nonmagnetic. Although Ti 3 N 2 favors AFM configuration with hexagonal crystal systems having 6/ mmm point group symmetry, Ti 3 N 2 does not support altermagnetism. The monolayer of the Ti 3 N 2 MXene is a ferromagnetic electride. These unique properties of having non-nuclear interstitial anionic electrons in the electronic structure of titanium nitride MXene have not yet been reported in the literature. Density functional theory calculations show TiN is neither an electride, MXene, or magnetic.

Anionic electrons↗
DOE OSTI2013

New orthorhombic derivative of CaCu{sub 5}-type structure: RNi{sub 4}Si compounds (R=Y, La, Ce, Sm, Gd–Ho), crystal structure and some magnetic properties

The crystal structure of new YNi{sub 4}Si-type RNi{sub 4}Si (R=Y, La, Ce, Sm, Gd–Ho) compounds has been established using powder X-ray diffraction. The YNi{sub 4}Si structure is a new structure type, which is orthorhombic derivative of CaCu{sub 5}-type structure (space group Cmmm N 65, oC12). GdNi{sub 4}Si and DyNi{sub 4}Si compounds order ferromagnetically at 25 and 19 K, respectively whereas YNi{sub 4}Si shows antiferromagnetic nature. At 15 K, DyNi{sub 4}Si shows second antiferromagnetic-like transition. The magnetic moment of GdNi{sub 4}Si at 5 K in 50 kOe field is ∼7.2 μ{sub B}/f.u. suggesting a completely ordered ferromagnetic state. The magnetocaloric effect of GdNi{sub 4}Si is calculated in terms of isothermal magnetic entropy change and it reaches the maximum value of −12.8 J/kg K for a field change of 50 kOe near T{sub C} ∼25 K. - Graphical abstract: The RNi{sub 4}Si (R=Y, La, Ce, Sm, Gd–Ho) compounds crystallize in new YNi{sub 4}Si-type structure which is orthorhombic derivative of the basic CaCu{sub 5}-type structure. GdNi{sub 4}Si and DyNi{sub 4}Si compounds show the ferromagnetic-like ordering, whereas.YNi{sub 4}Si has the antiferromagnetic nature. The GdNi{sub 4}Si demonstrates the big magnetocaloric effect near temperature of ferromagnetic ordering. The relationship between initial CaCu{sub 5}-type DyNi{sub 5} and YNi{sub 4}Si-type DyNi{sub 4}Si lattices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

A family of rare earth molybdenum bronzes: Oxides consisting of periodic arrays of interacting magnetic units

The family of rare earth molybdenum bronzes, reduced ternary molybdates of composition LnMo{sub 16}O{sub 44,} was synthesized and a detailed structural study carried out. Bond valence sum (BVS) calculations clearly show that the molybdenum ions in tetrahedral coordination are hexavalent while the electron count in the primitive unit cell is odd. Yet, measurements show that the phases are semiconductors. The temperature dependence of the magnetic susceptibility of samples containing several different rare earth elements was measured. These measurements verified the presence of a 6.5 K magnetic phase transition not arising from the rare earth constituent, but likely associated with the unique isolated ReO{sub 3}-type Mo{sub 8}O{sub 36} structural subunits in this phase. To better understand the behavior of these materials, electronic structure calculations were performed within density functional theory. Results suggest a magnetic state in which these structural moieties have an internal ferromagnetic arrangement, with small ~1/8 μ{sub B} moments on each Mo. We suggest that the Mo{sub 8}O{sub 36} units behave like pseudoatoms with spin 1/2 derived from a single hole distributed over the eight Mo atoms that are strongly hybridized with the O atoms of the subunit. Interestingly, while the compound is antiferromagnetic, our calculations suggest that a field-stabilized ferromagnetic state, if achievable, will be a narrow band half-metal. - Graphical abstract: LnMo{sub 16}O{sub 44} phases comprise corner sharing tetrahedral and octahedral molybdenum ions. The MoO{sub 6} octahedra form Mo{sub 8}O{sub 36} units that are well separated and act like pseudo-atoms, accommodating 11 electrons each. - Highlights: • Single crystal X-ray diffraction refinements of LnMo{sub 16}O{sub 44} single crystals for Ln=Ce, Pr, Nd, Tb, Dy and Ho. • DFT calculations based on LaMo{sub 16}O{sub 44}. • [Mo{sub 8}O{sub 36}] units behaving as superatoms with a net magnetic moment of 1 µ{sub B}. • Bronze structure containing equal number of molybdenum tetrahedra and octahedral.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Nd{sub 8}Co{sub 4−x}Al{sub x}Ge{sub 2}C{sub 3}: A case study in flux growth of lanthanide-rich intermetallics

The intermetallic Nd{sub 8}Co{sub 4−x}Al{sub x}Ge{sub 2}C{sub 3} (x≈0.65) was prepared from reaction of germanium and carbon in Nd/Co eutectic flux in an alumina crucible. This phase exhibits a new structure type in orthorhombic space group Pbcm, with unit cell parameters a=8.001(1) Å, b=11.696(2) Å, c=15.020(3) Å (Z=4; R{sub 1}=0.0234). The structure features germanium-centered neodymium clusters Ge@Nd{sub 9} which share faces to form layers separated by zigzag chains of cobalt atoms capped by carbon. Density of states calculations confirm that this compound is metallic, and indicate that the cobalt should not have a magnetic moment. This is supported by magnetic susceptibility measurements which show a low temperature ferromagnetic ordering at T{sub C}=50 K due to the Nd{sup 3+} ions. Magnetization field dependence studies on single crystals indicate this compound is a strong ferromagnet with large anisotropy; the Nd{sup 3+} magnetic moments align along the a-axis. - Graphical abstract: Nd{sub 8}Co{sub 4−x}Al{sub x}Ge{sub 2}C{sub 3} (x≈0.65) contains germanium-centered neodymium clusters Ge@Nd{sub 9} which share faces to form layers separated by zigzag chains of cobalt atoms capped by carbon. - Highlights: • Nd{sub 8}Ge{sub 2}Co{sub 3.35}Al{sub 0.65}C{sub 3} grows as large crystals from reactions in Nd/Co eutectic flux. • Structure features Ge@Nd{sub 9} clusters and zigzag cobalt chains capped by carbon. • Cobalt has no magnetic moment; Nd{sup 3+} ion moments order ferromagnetically. • Hard ferromagnet with strong anisotropy below T{sub C} of 50 K. • Flux growth and structural trends of lanthanide-rich intermetallics are reviewed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Giant magnetic coercivity in CaCu{sub 5}-type SmNi{sub 3}TSi (T=Mn–Cu) solid solutions

The effects of transition metal substitution for Ni on the magnetic properties of the CaCu{sub 5}-type SmNi{sub 3}TSi (T=Mn, Fe, Co, Cu) solid solutions have been investigated. SmNi{sub 3}MnSi, SmNi{sub 3}FeSi, SmNi{sub 3}CoSi and SmNi{sub 3}CuSi show ferromagnetic ordering at 125 K, 190 K, 46 K and 12 K and field induced transitions at 65 K, 110 K, 30 K and 6 K, respectively. The magnetocaloric effects of SmNi{sub 3}TSi (T=Mn, Fe, Co, Cu) were calculated in terms of isothermal magnetic entropy change (ΔS{sub m}). The magnetic entropy ΔS{sub m} reaches value of −1.1 J/kg K at 130 K for SmNi{sub 3}MnSi, −0.4 J/kg K at 180 K for SmNi{sub 3}FeSi, −0.37 J/kg K at 45 K for SmNi{sub 3}CoSi and −0.5 J/kg K at 12 K for SmNi{sub 3}CuSi in field change of 0–50 kOe around the ferromagnetic ordering temperature. They show positive ΔS{sub m} of +2.4 J/kg K at 30 K for SmNi{sub 3}MnSi, −2.6 J/kg K at 65 K for SmNi{sub 3}FeSi, +0.73 J/kg K at 15 K for SmNi{sub 3}CoSi and −0.5 J/kg K at 6 K for SmNi{sub 3}CuSi in field change of 0–50 kOe around the metamagnetic-like transition temperature. Below the field induced transition temperature, SmNi{sub 3}TSi (T=Mn, Fe, Co, Cu) exhibits giant magnetic coercivity of 80 kOe at 20 K for SmNi{sub 3}MnSi, 87 kOe at 40 K for SmNi{sub 3}FeSi, 27 kOe at 20 K for SmNi{sub 3}CoSi and 54 kOe at 5 K for SmNi{sub 3}CuSi. - Graphical abstract: CaCu{sub 5}-type SmNi{sub 3}MnSi, SmNi{sub 3}FeSi, SmNi{sub 3}CoSi and SmNi{sub 3}CuSi show ferromagnetic ordering at 125 K, 190 K, 46 K and 12 K and field induced transitions at 65 K, 110 K, 30 K and 6 K, respectively. The magnetic entropy ΔS{sub m} reaches value of −1.1 J/kg K at 130 K for SmNi{sub 3}MnSi, −0.4 J/kg K at 180 K for SmNi{sub 3}FeSi, −0.37 J/kg K at 45 K for SmNi{sub 3}CoSi and −0.5 J/kg K at 12 K for SmNi{sub 3}CuSi in field change of 0–50 kOe around the ferromagnetic ordering temperature. They show positive ΔS{sub m} of +2.4 J/kg K at 30 K for SmNi{sub 3}MnSi, −2.6 J/kg K at 65 K for SmNi{sub 3}FeSi, +0.73 J/kg K at 15 K for SmNi{sub 3}CoSi and −0.5 J/kg K at 6 K for SmNi{sub 3}CuSi in field change of 0–50 kOe around the metamagnetic-like transition temperature. Below the field induced transition temperature, SmNi{sub 3}TSi (T=Mn, Fe, Co, Cu) exhibits giant magnetic coercivity of 80 kOe at 20 K for SmNi{sub 3}MnSi, 87 kOe at 40 K for SmNi{sub 3}FeSi, 27 kOe at 20 K for SmNi{sub 3}CoSi and 54 kOe at 5 K for SmNi{sub 3}CuSi. - Highlights: • CaCu{sub 5}-type SmNi{sub 3}{Mn, Fe, Co, Cu}Si exhibit the Curie points at 12–190 K. • SmNi{sub 3}{Mn, Fe, Co, Cu}Si show field induced transition at 6–110 K. • SmNi{sub 3}MnSi shows huge magnetic hysteresis with coercive field of 80 kOe at 20 K. • SmNi{sub 3}FeSi shows huge magnetic hysteresis with coercive field of 87 kOe at 40 K. • SmNi{sub 3}CuSi shows giant coercive field of 54 kOe at 5 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Magnetic properties of Fe implanted SrTiO{sub 3} perovskite crystal

Graphical abstract: - Highlights: • The results of investigations of magnetic properties of Fe implanted SrTiO{sub 3} are presented. • The measurements of the temperature dependence of the magnetization were performed. • Ferromagnetic hysteresis loops in Fe implanted SrTiO{sub 3} were observed at low temperatures. • Superparamagnetic behavior of the samples at high temperatures was revealed. • It was shown that the magnetization of the samples depends on the fluency of implantation. - Abstract: The results of investigations of magnetic properties of SrTiO{sub 3} perovskite crystal implanted with 40 keV Fe ions at the fluencies between 0.5 × 10{sup 17} and 1.5 × 10{sup 17} ion/cm{sup 2} are presented. It has been revealed that high-fluency implantation with Fe ions results in the formation of a granular metal particulate composite in the irradiated near-surface layer of SrTiO{sub 3} substrate, which exhibits remarkable ferromagnetic behavior. The measurements of the temperature dependence of the magnetic moment showed that the samples exhibit blocking temperature at about 350 K, above which a superparamagnetic behavior has been observed. Ferromagnetic ordering and magnetic hysteresis loops were observed in Fe implanted SrTiO{sub 3} at the temperatures lower than 350 K. It has been shown that the magnetization of the ferromagnetic state depends on the fluency of implantation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Controlling the structure and ferroic properties of strained epitaxial NiTiO3 thin films on sapphire by post-deposition annealing

Ferroelectrically induced weak ferromagnetism had been predicted earlier in compounds MTiO3 (M = Fe, Mn, Ni) with the LiNbO3-type structure. In order to stabilize this metastable structure by oxide heteroepitaxy, we attempted to grow epitaxial NiTiO3 films on the nonpolar, non-magnetic substrate Al2O3 by pulsed laser deposition. Given the structural imperfections of the as-deposited films arising from the large lattice mismatch, which resulted in weak ferroic ordering, we investigated the effect of post-synthesis annealing on the films’ properties. Our structural data from x-ray diffraction and electron microscopy suggest that the crystalline quality of the NiTiO3 films was greatly improved by annealing the films at 600-1000 oC for 8 hours, with new phase formation along the interface at 1000 oC. Our physical property characterization indicates increased ferromagnetism and polarization after 600 oC, but a change in the magnetic state to likely ferrimagnetism, and a loss of polarization after the 1000 oC treatment. Our results suggest that the ferroic domain properties of the NiTiO3 films can be favorably altered by post-synthesis heat treatment at the proper temperature to manipulate interfacial strain and enhance the multiferroic properties. Improvement in the ferroic properties can be explained by a combination of crystallite growth, interfacial strain relief, and thermodynamic phase stability arguments. At the same time, exceeding temperatures may drive the system to a thermodynamically more favored crystalline order, and eventually to phase segregation and decomposition.

Varga, Tamas↗