The Laves phase compound, YCo2, is a well-known exchange-enahnced Pauli paramagnet. We report here that, in the nanocrystalline form, this compound interestingly is an itinerant ferromagnet at room temperature with a low coercive-field. The magnitude of the saturation moment (about 1 Bohr-magneton per formula unit) is large enough to infer that the ferromagnetism is not a surface phenomenon in these nanocrystallites. Since these ferromagnetic nanocrystallines are easy to synthesize with a stable form in air, one can explore applications, particularly where hysteresis is a disadvantage.
We have developed a simple, surfactant assisted synthesis route for the preparation, in gram quantities, of Co and Li doped ZnO nanocrystalline samples showing robust room temperature ferromagnetism. Our studies show that RTF is intrinsic to Zn0.85Co0.05Li0.10O and not due to any segregated secondary phases. In addition, it has been shown that the defects play an important role in activating RTF in these oxide systems. This also provide an explanation for the widely varying results observed in the literature. The method can also be extended for the synthesis of other transition metal doped ZnO…
Some of the Multiferroics [1] form a rare class of materials that exhibit magnetoelectric coupling arising from the coexistence of ferromagnetism and ferroelectricity, with potential for many technological applications.[2,3] Over the last decade, an active research on multiferroics has resulted in the identification of a few routes that lead to multiferroicity in bulk materials.[4-6] While ferroelectricity in a classic ferroelectric such as BaTiO3 is expected to diminish with the reducing particle size,[7,8] ferromagnetism cannot occur in its bulk form.[9] Here, we use a combination of experim…
We discuss the particle size driven tunability of the coexistence of ferromagnetism and ferroelectricity in Pr0.67Ca0.33MnO3(PCMO) with the help of x ray diffraction, magnetization, impedance spectroscopy, and remanent polarization measurements. The remanent polarization measurements using the positive up negative down method clearly prove the existence of ferroelectricity in PCMO with phase separation between Zener polaron(ZP) ordered P21nm and disordered Pbnm structures. We also find that the ferroelectric response is enhanced in nanocrystalline samples so long as ZP ordering is not destroye…
We study the ferromagnetism of La0.67Ca0.33MnO3 in bulk polycrystalline, nanocrystalline and amorphous phase. The structural change from crystalline phase to amorphous phase exhibited a systematic decrease of TC(paramagnetic to ferromagnetic transition temperature) and spontaneous magnetization (MS). The experimental results suggested few more features, e.g., appearance of large magnetic irreversibility in the temperature dependence of magnetization, lack of magnetic saturation at high magnetic field, blocking of magnetization below TB, and enhancement of coercivity. In addition, the magnetic …
A series on nanocrystalline Fe100-xCrx alloys prepared by mechanical alloying was investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM) and Mössbauer spectroscopy (MS) techniques. XRD and SEM were used to structurally characterize the samples whereas MS permitted phase analysis as well as determination of the Debye temperature, Theta_D. Concerning the latter, an enhancement relative to bulk Theta_D-values was revealed in the range of ca. 40 < x <50. In a sample of Fe55.5Cr44.5 two phases were detected viz. (1) crystalline and magnetic with Theta_D=572(56) K and (2) amor…
The compound alpha-Fe1.4Ga0.6O3 has been prepared by mechanical alloying of alpha-Fe2O3 and Ga2O3 and subsequent heating of the mechanical alloyed samples in vacuum condition. Magnetic ordering of alpha-Fe2O3 has been modified by substitution of non-magnetic Ga atoms. The ferromagnetism in alpha-Fe1.4Ga0.6O3 is more soft and enhanced in comparison to alpha-Fe2O3. Mössbauer spectroscopy also confirmed enhanced ferromagnetic order in alpha-Fe1.4Ga0.6O3. The room temperature soft ferromagnetism by Ga substitution is interesting for designing alpha-Fe2O3 based unconventional ferromagnet, which is …
We report on isothermal magnetization, Mössbauer spectroscopy, and magnetostriction as well as temperature-dependent alternating-current (ac) susceptibility, specific heat, and thermal expansion of single crystalline and polycrstalline Li$_2$(Li$_{1-x}$Fe$_x$)N with $x = 0$ and $x \approx 0.30$. Magnetic hysteresis emerges at temperatures below $T \approx 50\,$K with coercivity fields of up to $μ_0H = 11.6\,$T at $T = 2\,$K and magnetic anisotropy energies of $310\,$K ($27\,$meV). The ac susceptibility is strongly frequency dependent ($f\,=\,10$--$10,000\,$Hz) and reveals an effective energy b…
We observe remarkably strong room temperature ferromagnetism (~1.5 Bohr Magneton/Mn) in optically transparent Mn(II)-doped indium tin oxide (ITO) films. The nanocrystalline films with average grain size 10-22 nm and thickness 150-350 nm are prepared by sol-gel coating technique on sodalime silica glass substrate. The ferromagnetic property is, of course, weak for films deposited on pure silica glass substrate. The structural parameters of the films appear to be governing the magnetic property strongly which vary appreciably depending on the substrate. The observation of room temperature ferrom…
We have investigated the magnetic behavior of the nano crystals, synthesized by high-energy ball-milling, for a well-known geometrically frustrated spin-chain system, Ca3CoRhO6, and compared its magnetic characteristics with those of the bulk form by measuring ac and dc magnetization. The features attributable to the onset of 'partially disordered antiferromagnetism' (characterizing the bulk form) are not seen in the magnetization data of the nano particles; the magnetic moment at high fields in the very low temperature range in the magnetically ordered state gets relatively enhanced in the na…
We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin films using x-ray magnetic circular dichroism (XMCD) and resonance-photoemission spectroscopy. From the Mn 2$p$$\rightarrow3d$ XMCD results, it is shown that, while XMCD signals only due to paramagnetic Mn$^{2+}$ ions were observed in ZnO:Mn, nonmagnetic, paramagnetic and ferromagnetic Mn$^{2+}$ ions coexist in ZnO:Mn,N. XMCD signals of ZnO:Mn,N revealed that the localized Mn$^{2+}$ ground state and Mn$^{2+}$ state hybridized with ligand hole coexisted, implying $p$-$d$ exchange coupling. In the valence-band spectra, spe…
Recently d0 or intrinsic ferromagnetism was believed to provide an alternative pathway to transition metal induced ferromagnetism in oxide. In pursuit of augmenting the area of d0 ferromagnetism; we have undertaken to study the crystal structure and magnetic properties of Ag-doped ZrO2 compounds. Polycrystalline samples of Zr1-xAgxO2 (with x=0, 0.02, 0.04, 0.06 and 0.08) were prepared by solid-state reaction route. All the prepared compounds are found to crystallize in monoclinic symmetry of ZrO2. In our study, pure ZrO2 compound exhibits paramagnetic behavior. However, the Ag-doped ZrO2 compo…
Materials with negative thermal expansion (NTE), which contract upon heating, are of great interest both technically and fundamentally. Here, we report giant NTE covering room temperature in mechanically milled antiperovksite GaNxMn3 compounds. The micrograin GaNxMn3 exhibits a large volume contraction at the antiferromagnetic (AFM) to paramagnetic (PM) (AFM-PM) transition within a temperature window (ΔT) of only a few kelvins. The grain size reduces to ~ 30 nm after slight milling, while ΔT is broadened to 50K. The corresponding coefficient of linear thermal expansion (α) reaches ~ -70 ppm/K,…
Nanocrystalline (Th1-xFex)O2-d particles with different Fe concentrations (x = 0.0, 0.05, 0.10, 0.15, 0.20 and 0.25) have been prepared by a gel combustion method. Rietveld refinement analyses of X-ray diffraction data revealed the formation of an impurity free cubic type Th1-xFexO2-d structure up to x = 0.20. This observation is further confirmed from the detailed studies conducted on 10 at. percent Fe doped ThO2 using high-resolution transmission electron microscopy (HRTEM) imaging and indexing of the selected-area electron diffraction (SAED) patterns. DC Magnetization studies as a function …
Colloidal cobalt-doped TiO2 (anatase) nanocrystals were synthesized and studied by electronic absorption, magnetic circular dichroism, transmission electron microscopy, magnetic susceptibility, cobalt K-shell X-ray absorption spectroscopy, and extended X-ray absorption fine structure measurements. The nanocrystals were paramagnetic when isolated by surface-passivating ligands, weakly ferromagnetic (Ms = 1.5 x 10-3 mB/Co2+ at 300 K) when aggregated, and strongly ferromagnetic (up to Ms = 1.9 mB/Co2+ at 300 K) when spin-coated into nanocrystalline films. X-ray absorption data reveal that cobalt …
Magnetic properties of graphene with randomly distributed magnetic defects/vacancies are studied in terms of the Kondo Hamiltonian in the mean field approximation. It has been shown that graphene with defects undergoes a magnetic phase transition from a paramagnetic to a antiferromagnetic (AFM) phase once the temperature reaches the critical point $T_{N}$. The defect straggling is taken into account as an assignable cause of multiple nucleation into AFM domains. Since each domain is characterized by partial compensating magnetization of the defects associated with different sublattices, togeth…
Wurtzite GaN:Mn films on sapphire substrates were successfully grown by use of the molecular beam epitaxy (MBE) system. The film has an extremely high Curie temperature of around 940 K, although the Mn concentration is only about 3 ~ 5 %. Magnetization measurements were carried out in magnetic fields parallel to the film surface up to 7 T. The magnetization process shows the coexistence of ferromagnetic and paramagnetic contributions at low temperatures, while the typical ferromagnetic magnetization process is mainly observed at high temperatures because of the decrease of the paramagnetic con…
Structural and magnetic properties have been studied for polycrystalline Zn_1-xMn_xO (x=0.02, 0.03, 0.05). Low-temperature (~500 oC) synthesis leaves unreacted starting ZnO and manganese oxides. Contrary to a recent report, no bulk ferromagnetism was observed for single-phase materials synthesized in air at temperatures above 900 oC. Single-phase samples show paramagnetic Curie-Weiss behavior.
Detailed measurements of the magnetic and transport properties of the two La1-xCaxMnO3 (x = 0.18, x = 0.20) single crystals straddling the compositional metal-insulator transition boundary (0.18 < xc < 0.22) are summarized. The analysis of magnetization/susceptibility data reveals the occurrence of a second order/continuous ferromagnetic-paramagnetic phase transition described not only by nearest neighbour, 3-D Heisenberg model exponents (gamma = 1.387, beta = 0.365, delta = 4.783), but also with comparable values of the critical amplitudes in both the insulating and the metallic samples. Thes…
Ni3C nanoparticles of about 40 nm have been studied experimentally to exhibit weak ferromagnetic (FM), spin-glass (SG) and paramagnetic (PM) properties. The freezing temperature of the SG phase at zero applied field is determined as, TF0 ~ 11.0 K. At T > TF0, a very weak ferromagnetism has been observed over a PM background. The Curie temperature, TC, is shown to exceed 300 K and the ferromagnetism at 300 K is determined as about 0.02 emu/g (~6.7*10^{-4}mu_B per Ni3C formula unit) by subtracting the background paramagnetism. An anomalous dip appears in the temperature dependent coercivity, HC(…
We report here enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field upto 300K and a finite thermoremanent magnetization upto 340K for the annealed sample. We propose that magnetic moments can form at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers, or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagne…
The compounds Ca(Fe1-xNix)2As2 with the tetragonal ThCr2Si2-type structure (space group I4/mmm) show a continuous transition of the interlayer As-As distances from a non-bonding state in CaFe2As2 (dAs-As = 313 pm) to single-bonded As2-dimers in CaNi2As2 (dAs-As = 260 pm). Magnetic measurements reveal weak ferromagnetism which develops near the composition Ca(Fe0.5Ni0.5)2As2, while the compounds with lower and higher nickel concentrations both are Pauli-paramagnetic. DFT band structure calculations reveal that the As2-dimer formation is a consequence of weaker metal-metal in MAs4-layers (M = Fe…
We report a surfactant assisted synthesis of Mn doped ZnO polycrystalline samples showing robust room temperature ferromagnetism as characterized by X-ray diffraction analysis, Transmission Electron Microscopy, Electron Paramagnetic Resonance and DC magnetization mearurements. This surfactant assisted synthesis method, developed by us, is found to be highly reproducible. Further, it can also be extended to the synthesis of other transition metal doped ZnO.
In a quest of enriching the area of d0 magnetism in oxide materials, we have undertaken to study Mg-doped TiO2 compounds. The Ti1-xMgxO2 (x=0, 0.02, 0.04 and 0.06) nanoparticles were prepared by solid-state reaction route. The X-ray diffractions (XRD) patterns of these samples indicate single phase of tetragonal rutile-structure of TiO2. The refinement of the XRD patterns reveals no change in the crystallographic lattice parameters in comparison to pure TiO2 upon Mg doping and it indicates that Mg2+ ions do not enter core grains and form core/shell structure. SEM observations reveal the unifor…
The nature of the often reported room temperature ferromagnetism in transition metal doped oxides is still a matter of huge debate. Herein we report on room temperature ferromagnetism in high quality Co-doped ZnO (Zn1-xCoxO) bulk samples synthesized via standard solid-state reaction route. Reference paramagnetic Co-doped ZnO samples with low level of structural defects are subjected to heat treatments in a reductive atmosphere in order to introduce defects in the samples in a controlled way. A detailed structural analysis is carried out in order to characterize the induced defects and their co…
The evolution between Fermi liquid and non-Fermi-liquid states in correlated electron systems has been a central subject in condensed matter physics because of the coupled intriguing magnetic and electronic states. An effective pathway to explore the nature of non-Fermi liquid behavior is to approach its phase boundary. Here we report a crossover from non-Fermi liquid to Fermi-liquid state in metallic CaRuO3 through ionic liquid gating induced protonation with electric field. This electronic transition subsequently triggers a reversible magnetic transition with the emergence of an exotic ferro…
Using the spectroscopies based upon x-ray absorption, we have studied the structural and magnetic properties of Zn$_{1-x}$Co$_{x}$O films ($x$ = 0.1 and 0.25) produced by reactive magnetron sputtering. These films show ferromagnetism with a Curie temperature $T_{\mathrm{C}}$ above room temperature in bulk magnetization measurements. Our results show that the Co atoms are in a divalent state and in tetrahedral coordination, thus substituting Zn in the wurtzite-type structure of ZnO. However, x-ray magnetic circular dichroism at the Co \textit{L}$_{2,3}$ edges reveals that the Co 3\textit{d} sub…
We use the Kondo lattice model to investigate the possibility of ferromagnetism and half-metallicity in local moment systems. Using the spectral density approach and making use of the fact that the spontaneous magnetization of local moment and the itinerant electron polarization are coupled, we derive an expression for the paramagnetic susceptibility. The magnetic ordering temperature is determined from the singularities of the susceptibility. The magnetic phase diagram is constructed in $T-n$(band filling) plane. It is found that ferromagnetism is possible only for small values of $n$. It is …
We have examined whether the Co ions crystallographically substitute on the Ti sites in rutile and anatase Ti_{1-x}$Co$_{x}$O$_{2-delta}$ thin films that exhibit room-temperature ferromagnetism. Intensities of the x-ray Bragg reflection from the films were measured around the $K$-absorption-edge of Co. If the Co ions randomly substitute on the Ti sites, the intensity should exhibit an anomaly due to the anomalous dispersion of the atomic scattering factor of Co. However, none of the anatase and rutile samples did exhibit an anomaly, unambiguously showing that the Co ions in Ti$_{1-x}$Co$_{x}$O…
We investigated the reversible ferromagnetic (FM) behavior of pure and Co doped CeO2 nanopowders. The as-sintered samples displayed an increasing paramagnetic contribution upon Co doping. Room temperature FM is obtained simply by performing thermal treatments in vacuum at temperatures as low as 500^{\circ}C and it can be switched off by performing thermal treatments in oxidizing conditions. The FM contribution is enhanced as we increase the time of the thermal treatment in vacuum. Those systematic experiments establish a direct relation between ferromagnetism and oxygen vacancies and open a pa…
We report the successful passivation of the Mn acceptors in GaMnP upon exposure to a remote dc hydrogen plasma. The as-grown films are non-metallic and ferromagnetic with a Curie temperature of T_C=55K. After hydrogenation the sample resistivity increases by approximately three orders of magnitude at room temperature and six orders of magnitude at 25 K. Furthermore, the hydrogenated samples are paramagnetic, which is evidenced by a magnetization curve at 5 K that is best described by a Brillouin function with g=2 and J=5/2 expected for Mn atoms in the 3d^5 configuration. These observations una…
We report on the synthesis of single crystalline and polycrystalline samples of Ce$_{3-x}$Mg$_x$Co$_9$ solid solution ($0\leq x \lesssim 1.4$) and characterization of their structural and magnetic properties. The crystal structure remains rhombohedral in the whole composition range and Mg partially replaces Ce in the 6\textit{c} site of the CeCo$_3$ structure. Ferromagnetism is induced by Mg substitutions starting as low as $x=0.18$ and reaching a Curie temperature as high as $450$\,K for $x=1.35$. Measurements on single crystals with $x=1.34$ and $T_\textrm{C}=440$\,K indicate an axial magnet…
Considering a general situation where a semiconductor is doped by magnetic impurities leading to a carrier-induced ferromagnetic exchange coupling between the impurity moments, we show theoretically the possible generic existence of three ferromagnetic transition temperatures, T_1 > T_2 > T_3, with two distinct ferromagnetic regimes existing for T_1 > T > T_2 and T < T_3. Such an intriguing re-entrant ferromagnetism, with a paramagnetic phase (T_2 > T > T_3) between two ferromagnetic phases, arises from a subtle competition between indirect exchange induced by thermally activated carriers in a…
A mechanism of the high temperature ferromagnetism in polymerized fullerenes is suggested. It is assumed that some of the C$_{60}$ molecules in the crystal become magnetically active due to spin and charge transfer from the paramagnetic impurities (atoms or groups), such as hydrogen, fluorine, hydroxyl group OH, amino group NH$_2$, or methyl group CH$_3$, dispersed in the fullerene matrix. The exchange interaction between the spins localized on the magnetically active fullerenes is evaluated using \textit{ab initio} calculations. The nearest neighbour and next nearest neighbour exchange intera…
Inducing ferromagnetism by structural engineering in a strongly spin-orbit coupled oxide
Universität Würzburg（维尔茨堡大学）；International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences（波兰科学院物理研究所磁顶国际研究中心）；CNR-SPIN, UOS Salerno（萨莱诺国家研究委员会自旋单元）；Leibniz Institute for Solid State and Materials Research Dresden（德累斯顿莱布尼兹固体与材料研究所）；TU Dresden（德累斯顿工业大学）；Synchrotron SOLEIL（索雷尔同步辐射中心）
Magnetic properties of (Ga,Mn)As/GaAs superlattices are investigated. The structures contain magnetic (Ga,Mn)As layers, separated by thin layers of non-magnetic GaAs spacer. The short period Ga$_{0.93}$Mn$_{0.07}$As/GaAs superlattices exhibit a paramagnetic-to-ferromagnetic phase transition close to 60K, for thicknesses of (Ga,Mn)As down to 23 Å. For Ga$_{0.96}$Mn$_{0.04}$As/GaAs superlattices of similar dimensions, the Curie temperature associated with the ferromagnetic transition is found to oscillate with the thickness of non magnetic spacer. The observed oscillations are related to an inte…
The effect of hydrogenation on magnetic properties of Zn0.85Co0.05Li0.10O nanoparticles is presented. It was found that the sample hydrided at room temperature (RT) showed weak ferromagnetism (FM) while that hydrided at 400oC showed robust ferromagnetism at room temperature. In both cases reheating the sample at 400oC in air converts it back into paramagnetic state (P) completely. The characterization of samples by X-ray and electron diffraction (ED) showed that room temperature ferromagnetism observed in the samples hydrogenated at RT is intrinsic in nature whereas that observed in the sample…
The first-principles full-potential linearized augmented plane-wave method based on density functional theory is used to investigate electronic structure and magnetic properties of hypothetical binary compounds of I$^{A}$ subgroup elements with nitrogen (LiN, NaN, KN and RbN) in assumed three types of cristalline structure (rock salt, wurtzite and zinc-blende). We find that, due to the spin polarized \textit{p} orbitas of N, all four compounds are half-metallic ferromagnets with wide energy bandgaps (up to 2.0 eV). The calculated total magnetic moment in all investigated compounds for all thre…
Perovskite manganite La0.5Ca0.5-x xMnO3 (LCMO) nanomaterials were elaborated using the sucrose modified auto combustion method. Rietveld refinements of the X-ray diffraction patterns of the crystalline structure confirm a single-phase orthorhombic state with Pbnm space group (No. 62). The Ca-vacancies were voluntarily created in the LCMO structure in order to study their influence on the magnetic behaviour in the system. The magnetic susceptibility was found to be highly enhanced in the sample with Ca-vacancies. Paramagnetic-to-ferromagnetic phase transition was evidenced in both samples aroun…
Fe-doped ZnO nanocrystals are successfully synthesized and structurally characterized by using x-ray diffraction and transmission electron microscopy. Magnetization measurements on the same system reveal a ferromagnetic to paramagnetic transition temperature > 450 K with a low-temperature transition from ferromagnetic to spin-glass state due to canting of the disordered surface spins in the nanoparticle system. Local magnetic probes like EPR and Mossbauer indicate the presence of Fe in both valence states Fe2+ and Fe3+. We argue that the presence of Fe3+ is due to the possible hole doping in t…
We develop a quantitatively predictive theory for impurity-band ferromagnetism in the low-doping regime of GaMnAs and compare with experimental measurements of a series of samples whose compositions span the transition from paramagnetic insulating to ferromagnetic conducting behavior. The theoretical Curie temperatures depend sensitively on the local fluctuations in the Mn-hole binding energy, which originates from disorder in the Mn distribution as well as the presence of As antisite defects. The experimentally-determined hopping energy at the Curie temperature is roughly constant over a seri…
The possibility to induce long range ferromagnetic order by doping oxides with transition metal ions has become a very exciting challenge in the last decade. Theoretically, it has been claimed that Mn doped ZrO$_2$ could be a very promising spintronic candidate and that high critical temperatures could be already achieved even for a low Mn concentration. Some experiments have reported room temperature ferromagnetism (RT-FM) whilst some others only paramagnetism. When observed, the nature of RT-FM appears to be controversial and not clearly understood. In this study, we propose to clarify and s…
In a recent letter, it has been predicted within first principle studies that Mn-doped ZrO2 compounds could be good candidate for spintronics application because expected to exhibit ferromagnetism far beyond room temperature. Our purpose is to address this issue experimentally for Mn-doped tetragonal zirconia. We have prepared polycrystalline samples of Y0.15(Zr0.85-yMny)O2 (y=0, 0.05, 0.10, 0.15 & 0.20) by using standard solid state method at equilibrium. The obtained samples were carefully characterized by using x-ray diffraction, scanning electron microscopy, elemental color mapping, X-ray …
We report on the structural, electrical transport, and magnetic properties of antiferromagnetic transition-metal monochalcogenide Cr$_{0.79}$Se. Different from the existing off-stoichiometric compositions, Cr$_{0.79}$Se is found to be synthesised into the same NiAs-type hexagonal crystal structure of CrSe. Resistivity data suggest Cr$_{0.79}$Se to be a Fermi-liquid-type metal at low temperatures, while at intermediate temperatures the resistivity depends sublinearly on the temperature. Eventually, at the elevated temperatures the rate of change of resistivity rapidly decreases with increasing …
We report results of a Monte Carlo study of doped, diluted magnetic semiconductors in the low carrier density (insulating) regime. We find that the system undergoes a transition from a paramagnet at high temperatures to a ferromagnet at low temperatures. However, in strong contrast to uniform systems, disorder effects dominate the entire collective behavior, leading to very unconventional properties such as (1) magnetization curves that cannot be described by theories based on critical fluctuations, or on spin wave analysis over any significant fraction of the phase diagram; (2) a large peak i…
The Anomalous Hall Effect (AHE) is an important quantity in determining the properties and understanding the behavior of the two-dimensional electron system forming at the interface of SrTiO3-based oxide heterostructures. The occurrence of AHE is often interpreted as a signature of ferromagnetism, but it is becoming more and more clear that also paramagnets may contribute to AHE. We studied the influence of magnetic ions by measuring intermixed LaAlO3/GdTiO3/SrTiO3 at temperatures below 10 K. We find that, as function of gate voltage, the system undergoes a Lifshitz transition, while at the sa…
We demonstrate control of the magnetism of Pd(100) ultrathin films, which show d-electron quantum-well induced ferromagnetism, via modulation of the interface electronic state using density functional calculation. From an analysis based on the phase model, forming the Au/Pd(100) interface induces hybridization of the wave function of d-electron quantum-well states, and modulates the term of the scattering phase shift as a function of the reciprocal lattice point. In contrast, forming the Al interface, which has only s-electrons at the Fermi energy, cannot modify the scattering phase shift. Our…
The subtle interplay of randomness and quantum fluctuations at low temperatures gives rise to a plethora of unconventional phenomena in systems ranging from quantum magnets and correlated electron materials to ultracold atomic gases. Particularly strong disorder effects have been predicted to occur at zero-temperature quantum phase transitions. Here, we demonstrate that the composition-driven ferromagnetic-to-paramagnetic quantum phase transition in Sr1-xCaxRuO3 is completely destroyed by the disorder introduced via the different ionic radii of the randomly distributed Sr and Ca ions. Using a …
Ni$_{1-x}$Rh$_x$ bulk alloys exhibit a ferromagnetic to paramagnetic quantum phase transition (QPT) at the critical concentration $x_c \sim$ 0.37. A spin glass phase arises below the Ferromagnetism by controlling the short range interaction between Ni and Rh atoms. we have synthesized nanoalloys of two different concentrations with two different reaction times by chemical reflux method. From the dc magnetization measurements, existence of ferromagnetism and spin glass phase in these nanoalloys is confirmed. A step like feature in both ZFC and FC curve at certain temperature indicates the exist…
Electrically induced ferromagnetism in an irradiated complex oxide
University of California, San Diego（加州大学圣迭戈分校）；University of Denver（丹佛大学）；University of California, Davis（加州大学戴维斯分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
We report pulsed laser deposition synthesis and characterization of polycrystalline Fe1-xCox Si thin films on Si (111). X-ray diffraction, transmission electron, and atomic force microscopies reveal films to be dense, very smooth, and single phase with a cubic B20 crystal structure. Ferromagnetism with significant magnetic hysteresis is found for all films including nominally pure FeSi films in contrast to the very weak paramagnetism of bulk FeSi. For Fe1-xCoxSi this signifies a change from helimagnetism in bulk, to ferromagnetism in thin films. These ferromagnetic thin films are promising as …
