Glassy Ferromagnetism Research Articles

Magnetic glassy state in combination with ferromagnetism in Fe0.05(SnTe)0.97Sb0.03 bulk alloy

In this study on Fe0.05(SnTe)0.97Sb0.03 bulk alloy, we found signatures of presence of both magnetic glassy state and ferromagnetism. The bulk alloy is prepared by modified solid state technique and the sample is characterized for its structural, electrical and magnetic properties. Electrical resistivity plot shows semiconducting nature of the sample, however below 25 K, a sudden increase in the electrical resistivity value is observed. The transport mechanism is explained on the basis of small polaron hopping (SPH) model and variable range hopping (VRH) model. A large bifurcation observed between zero-field cooled and field-cooled magnetization at low temperature hints towards existence of a magnetic glassy state. M-H curve exhibits hysteresis behaviour for the measurements carried out at 10, 100 and 300 K. However, absence of saturation of the curves at 10 and 100 K suggests co-existence of ferromagnetic and glassy state. Presence of magnetic glassy state can also be confirmed from the Arrott plot and AC Susceptibility measurement. The susceptibility curves are found to undergo relatively small shift of peaks with frequency and theoretical fitting of the data supports presence of a cluster-glass state.

Structural, magnetic and electrical characterization of the La0.7Ca0.3Co1–x MnxO3 (x=0, 0.7 and 1) compounds prepared by a simple method

Structural, magnetic and electrical properties of the La0.7Ca0.3Co1–xMnxO3 (x=0, 0.7 and 1) samples prepared by a simple method were systematically studied and it was found that the crystal structure was transformed from rhombohedral for La0.7Ca0.3CoO3 (LCCO) and La0.7Ca0.3Co0.3Mn0.7O3 (LCCMO) samples to orthorhombic for La0.7Ca0.3MnO3 (LCMO) sample. The AC magnetic susceptibility measurements showed that LCCO sample underwent a transition from paramagnetic (PM) to ferromagnetic (FM) phase at Curie temperature, TC∼155 K and below Curie temperature, the glassy ferromagnetism nature was observed. In LCCMO sample, clear evidence of spin glass (SG) state was observed at low temperature. PM-FM phase transition at about TC∼260 K and long range FM order at low temperatures were observed in LCMO sample. Both the LCCO and LCCMO samples exhibited insulating behavior in the whole range of measuring temperature whereas the LCMO sample underwent a clear metal-insulator (MI) transition at about TMI∼263 K, corresponding to Curie temperature. Metallic region of ρ(T) curve of the LCMO sample was fitted to the model of electron-electron and electron-magnon scattering. The charge carrier transport behavior in all the samples was compared based on polaronic models.

Electrical, magnetic, and magneto-electrical properties in quasi-two-dimensional K0.58RhO2 single crystals doped with rare-earth elements

In this Letter, we studied the electrical transport, magnetic property, magnetoresistance and anomalous Hall properties of La-, Sm-, Ho-, and Dy-doped quasi-two dimensional K0.58RhO2 single crystals. At low temperature (<10 K), a significant magnetoresistance (36%) can be observed in these samples. Accordingly, the “glassy ferromagnetism” is revealed by temperature-dependent magnetization in these samples. The significant magnetoresistance is related to the granular ferromagnetism. The unconventional anomalous Hall effect is also observed in magnetic atoms doped samples. Our finding shields more light on the magnetic, magnetoresistance, and anomalous Hall properties of quasi-two-dimensional material systems doped with magnetic ions.

Evidence of glassy ferromagnetic phase and kinetic arrest of electronic phase in Sm0.35Pr0.15Sr0.5MnO3 manganites

The effect of doping of rare earth Pr3+ ion as a replacement of Sm3+ in Sm0.5Sr0.5MnO3 is investigated. Temperature dependent dc and ac magnetic susceptibility, resistivity, magnetoresistance measurements on chemically synthesized (Sm0.5−xPrx)Sr0.5MnO3 show various unusual features with doping level x=0.15. The frequency independent ferromagnetic to paramagnetic transition at higher temperature (∼191K) followed by a frequency dependent reentrant magnetic transition at lower temperature (∼31K) has been observed. The nature of this frequency dependent reentrant magnetic transition is described by a critical slowing down model of spin glasses. From non-linear ac susceptibility measurements it has been confirmed that the finite size ferromagnetic clusters are formed as a consequence of intrinsic phase separation, and undergo spin glass-like freezing below a certain temperature. There is an unusual observation of a 2nd harmonic peak in the non-linear ac susceptibility around this reentrant magnetic transition at low temperature (∼31K). Arrott plots at 10 and 30K confirm the existence of glassy ferromagnetism below this low temperature reentrant transition. Electronic- and magneto-transport measurements show a strong magnetic field—temperature history dependence and strong irreversibility with respect to the sweeping of magnetic field. These results are attributed to the effect of phase separation and kinetic arrest of the electronic phase in this phase separated manganite at low temperatures.

Glassy ferromagnetism and phase separation in Pr0.5Ca0.5CoO3

The dc and ac susceptibilities, magnetization curves and long-time relaxation were measured on a stoichiometric polycrystalline sample of Pr0.5Ca0.5CoO3. The compound shows a metal-insulator transition at TM-I=76 K, associated with combined spin-state and valency transformation of cobalt ions. Below 10 K the onset of a glassy ferromagnetism (Tf≈6.5 K) is observed, characterized by a frequency dependent susceptibility, S-type character of the virgin curve and ageing effect. An anomalously constricted hysteresis loop at T=Tf accompanied by a minimum in the temperature dependence of the coercivity was ascribed to an interaction between the glassy ferromagnetic and additional minor FM phase.

Magnetic Properties of Nanocrystalline β-SiC

Four-hour ball-milled beta-SIC product synthesized by the thermal plasma technique shows room temperature ferromagnetism. The semi-lambda signature of the field-cooled magnetization (FCM) and zero field-cooled magnetization (ZFCM) curves suggest the possible signature of a glassy ferromagnetism state in the sample. The prominent fall in the magnetization value at around 50 K observed in ZFCM curve reveals the existence of a sharp transition from a ferromagnetic state to a glassy ferromagnetic state. The presence of glassy ferromagnetism at low temperature is confirmed from the M-H curve recorded at 5 K.

No room temperature ferromagnetism in Mn over-doped Zn 1− xMn xO ( x>0.02)

Mn-doped ZnO samples having composition Zn 1− x Mn x O ( x=0.02, 0.04 and 0.05) were synthesized by solid state reaction technique with varying concentration of Mn from 0.02 to 0.05. Evidence of room temperature ferromagnetism was observed only in the composition Zn 0.98Mn 0.02O sintered at 500 °C. Our XRD pattern confirms the presence of Mn 3O 4 impurity phase in all the Zn 1− x Mn x O samples with the exception of Zn 0.98Mn 0.02O. We emphasize that the appearance of Mn 3O 4 phase in the system forbids the exchange type of interaction between the Mn ions and suppresses the ferromagnetism in all the Mn over-doped Zn 1− x Mn x O ( x>0.02) system. SEM microstructure study also supports the interruption of exchange type of interaction inside the system with the increase in Mn concentration in the sample. Interestingly, for this particular composition, Zn 0.98Mn 0.02O sintered at 500 °C, glassy ferromagnetism type of transition is observed at low temperature. This type of transition is attributed to the formation of the oxides of Mn clusters at low temperature.

Structural and magnetic properties of (Al, Fe)-codoped SiC

In this study, as a first attempt, we choose Al and transition metals (TMs), Fe, as codoping atoms to synthesize (Al, TM)-codoped SiC. X-ray diffraction and Raman analysis showed that a series of single-phase codoped 4H-SiC samples were obtained and no trace of any other impurity phases, such as Fe3Si and polytypes of other types of SiC, was found. Measurement of magnetic properties showed that codoping by Al and Fe elements changed the original glassy ferromagnetism (FM) features in Al-doped SiC and induced a robust room temperature FM order that gradually dominated (Al, Fe)-codoped 4H-SiC with increase in Fe content. The contribution of Al elements to the magnetic properties of (Al, Fe)-codoped 4H-SiC can be neglected and the magnetic origin should be ascribed to be induced by Fe doping. The only major role of Al is to stabilize the codoped crystal structure as 4H- single phase. As the first investigation on (Al, TM)-codoped SiC, this study opens a new pathway to obtain TM-doped SiC-based diluted magnetic semiconductors with a high Tc via the codoping strategy.

Glassy ferromagnetism in Al-doped 4 H-SiC: Al Si– [formula omitted] complexes

The recent observed glassy ferromagnetism in Al-doped 4 H-SiC is investigated using first principles calculations. We find that the formation energy of V C is significantly reduced by Al atoms doped in SiC. The Al Si– V C complex induces a half-filled narrow a 1 level in the band gap and contributes a net local moment of 1 μ B . The exchange parameter J can be either positive or negative along different directions. Both the strong anisotropy of J and the correlation effects of the a 1 level can lead to a glassy ferromagnetism in Al-doped 4 H-SiC.

Observation of Glassy Ferromagnetism in Al-Doped 4H-SiC

Glassy ferromagnetism is observed in diluted magnetic semiconductor Al-doped 4H-SiC. We propose a possible explanation for the origin of ferromagnetism order that is the coeffect of sp(2)/sp(3) configuration along with the structural defects. This result unambiguously demonstrates the existence of intrinsic ferromagnetism order in nonmagnetic sp systems.

Glassy ferromagnetism inNi3Sn-typeMn3.1Sn0.9

Magnetic measurements indicate that the glassy ferromagnetism exists in the ordered intermetallic ${\mathrm{Mn}}_{3.1}{\mathrm{Sn}}_{0.9}$ compound with ${\mathrm{Ni}}_{3}\mathrm{Sn}$-type structure. This glassy ferromagnetism exhibits both weak canonical behaviors, including a susceptibility sharp peak at ${T}_{f}=31.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and the frequency-dependent susceptibility below ${T}_{f}$, and long-range ferromagnetic ones, including a large coercivity and a magnetization increase after field-cooled below ${T}_{f}$. The glassy component is ascribed to both a small amount of disorder, arising from the random occupation of $2c$ sites in the space group $P{6}_{3}∕mmc$ by excess Mn atoms, and the common frustration. A power law for the critical slowing down gives the flipping time ${\ensuremath{\tau}}_{0}=3.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$, the collective freezing temperature ${T}_{g}=31.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and the dynamical exponent $z\ensuremath{\nu}=3.38$.

Glassy ferromagnetism and frustration in La0.7Ba0.3Mn0.7Ti0.3O3

Glassy ferromagnetism and the magnetic frustration effect in La0.7Ba0.3Mn0.7Ti0.3O3 were investigated by means of dc magnetization, ac susceptibility, and electron-spin-resonance (ESR) measurements. As a result, the spin-glass (SG) phase-transition temperature, Tg, was observed at 27.6 K. The in-phase component of the ac susceptibility χ′(T) indicated that the SG freezing temperature, Tf, shifted to low temperatures with lowering frequency. Dynamic processes on the frequency dependence of Tf have been analyzed by the slowing-down scaling law, τ∕τ0∝(Tf∕Tg−1)−zv, where the characteristic time τ0 and an exponent zv obtained were about 3.7×10−16s and 9.66, respectively. The microscopic picture characterizing phase separation and competing interactions in the compound were observed by ESR.

Small polaron transport and glassy ferromagnetism in (LaSr)Co 1− xFe xO 4

We have studied transport and magnetic properties of (LaSr)Co 1− x Fe x O 4 system. The conduction of (LaSr)CoO 4 is three-dimensional variable range hopping at low temperatures below ∼300 K and is expected to be thermally activated hopping above ∼900 K. With increasing x the electronic conduction changes from a variable range hopping type to a band-gap type between x = 0.2 and 0.6. Substitution of Co by Fe induces ferromagnetism with large hysteresis in the temperature dependence of magnetization below the transition temperature. This glassy ferromagnetism appears in the concentration region where the variable range hopping of small polaron is dominant. In the samples with x ≥ 0.6 the temperature dependence of magnetization shows an antiferromagnetic behavior. The lattice parameters a and c increase with increasing x. However, the increasing rate of c-axis is small in the variable hopping region below x ∼ 0.2. The values of resistivity and ferromagnetic moment become maximum around x = 0.2. The transport and magnetic properties have a close correlation in this system.

Beyond TCNE: new building blocks for molecule-based magnets

Several new examples of organic one-electron acceptors have been discovered to be viable and versatile alternatives to tetracyanoethylene as building blocks for the synthesis of charge-transfer salt/charge-transfer polymer molecule-based magnets. Guidelines for the identification of new acceptor candidates as well as several examples of compounds derived from these acceptors will be described. The observed magnetic properties include glassy ferromagnetism, metamagnetism and ferrimagnetism.

Interaction of alpha particle beams with metallic glasses

Samples of Fe 40Ni 38Mo 4B 18, Fe 78B 13Si 9 and Fe 66Co 18B 15Si 1 metallic glasses, selected with respect to the different values of their magnetostriction constants, were irradiated with alpha particle beams ( W=2.8 MeV) using radiation doses of 10 16 and 10 17/cm 2. The fundamental effects underlying the interaction of alpha particle beams with amorphous magnets were studied by transmission and conversion electron Mössbauer spectroscopy (CEMS), hysteresis loops and a.c. susceptibility measurements, and scanning electron microscopy (SEM). The evolution of phases and microstructure during the radiation-induced amorphous-to-crystalline transformation was found to depend on the particle flux and sample composition. Differences between bulk and surface behaviors of the magnetic texture and constituent phases were evidenced. Radiation-driven changes in the saturation magnetic moment, coercive field, real and imaginary components of the a.c. response were observed for all samples studied and found to depend on the radiation dose employed. The surface morphology of the radiation-induced crystalline precipitates was shown to vary as a function of composition, such that both spherical and dendritical modes of growth were observed. By stimulating unconventional pathways for the crystallization process, the interaction of alpha particle beams with glassy ferromagnets offers unique opportunities to understand the fundamentals of nucleation and growth in these systems.

Formation of magnetite particles by pulsed laser processing of Fe81B13.5Si3.5C2 metallic glass

In the present work the authors report new investigations on the fundamentals of pulsed laser interactions with glassy ferromagnets by considering laser sources with longer wavelengths and pulse widths. The formation mechanism of iron-oxide precipitates on the irradiated surfaces and the coexistence of oxidation effects with amorphous-to-crystalline transformations in iron-based glassy ferromagnets is studied as a function of laser processing parameters.

Evidence for phase selectivity in excimer-laser-induced amorphization of thermally annealed Fe66Co18B15Si glassy ferromagnet.

Pulsed-excimer-laser irradiation effects ($\ensuremath{\lambda}=308$ nm, $\ensuremath{\tau}=10$ ns) on the magnetic properties and phase composition of ${\mathrm{Fe}}_{66}$${\mathrm{Co}}_{18}$${\mathrm{B}}_{15}$Si metallic glass have been studied by transmission and conversion electron M\ossbauer spectroscopy, scanning electron microscopy, and energy-dispersive x-ray analysis. Depending on the number of applied pulses, excimer laser irradiation of amorphous ${\mathrm{Fe}}_{66}$${\mathrm{Co}}_{18}$${\mathrm{B}}_{15}$Si was found to induce controlled changes in the magnetic anisotropy without onset of bulk crystallization. Excimer-laser-induced amorphization was observed in partially crystallized ${\mathrm{Fe}}_{66}$${\mathrm{Co}}_{18}$${\mathrm{B}}_{15}$Si samples (${T}_{a}=648$ K, ${t}_{a}=1$ h) and was found to be accompanied by the development of laser-induced magnetic anisotropy. In completely crystallized ${\mathrm{Fe}}_{66}$${\mathrm{Co}}_{18}$${\mathrm{B}}_{15}$Si specimens (${T}_{a}=723$ K, ${t}_{a}=1$ h), which contained two crystalline phases of $\ensuremath{\alpha}$-(FeCo) and ${(\mathrm{FeCo})}_{3}$(BSi), the effect of excimer-laser-induced amorphization exhibited phase selectivity with respect to the crystalline components of the alloy system. By a combination of complementary methods, the laser-induced phase transformation of thermally annealed ${\mathrm{Fe}}_{66}$${\mathrm{Co}}_{18}$${\mathrm{B}}_{15}$Si specimens was shown to consist of partial amorphization and surface oxidation of the irradiated material. When compared to bulk data, a different behavior of the surface magnetic texture and relative abundance of alloy phases was observed. In both as-quenched and excimer-laser-irradiated amorphous ${\mathrm{Fe}}_{66}$${\mathrm{Co}}_{18}$${\mathrm{B}}_{15}$Si, the hyperfine field ${H}_{\mathrm{hf}}(T)$ exhibited a temperature dependence of ${H}_{\mathrm{hf}}(0)[1\ensuremath{-}{B}_{\frac{3}{2}}{(\frac{T}{{T}_{C}})}^{\frac{3}{2}}]$ indicative of spin-wave excitations. The value ${B}_{\frac{3}{2}}=0.32\ifmmode\pm\else\textpm\fi{}0.05$ of the temperature coefficient for the amorphous specimen is twice that obtained for the laser-irradiated ${\mathrm{Fe}}_{66}$${\mathrm{Co}}_{18}$${\mathrm{B}}_{15}$Si system. It is concluded that laser-induced quenching stresses reduce the fluctuations of exchange interactions in the irradiated sample. This study suggests that excimer-laser irradiation of glassy ferromagnets offers the intriguing opportunity of designing materials with specific combinations of magnetic and structural properties, not obtainable by conventional methods.

Interaction of Alpha Particle Beams with Fe-Based and FeNi-Based Glassy Ferromagnets

AbstractSamples of Fe78B13Si9 and Fe40Ni38Mo4B18 metallic glasses were irradiated with alpha particle beams (W=2.8 MeV) using radiation doses of 1016 and 1017 cm-2. Irradiation-induced effects on the magnetic texture and phase composition of alloy samples were studied by Mössbauer spectroscopy. Related morphological changes and resultant crystalline precipitates were characterized by scanning electron microscopy. The evolution of phases and microstructure during the radiation-induced amorphous-to-crystalline transformation was found to depend on the particle flux and sample composition. The lowest radiation dose employed was found to be more effective in inducing amorphous-to-crystalline transformations in both ferromagnetic alloys studied. In addition, the FeNi-based amorphous system investigated was found to be more stable than the Fe-based metallic glass, exposed to the same particle-beam irradiation conditions. By stimulating unconventional pathways for the crystallization process, the interaction of alpha particle beams with glassy ferromagnets offers unique opportunities to understand the fundamentals of nucleation and growth in amorphous magnets.

The magnetic properties of the glassy ferromagnets Fe81.5B14.5Si4 and Fe40Ni40B20

The galssy ferromagnets Fe81.5B14.5Si4 and Fe40Ni40B20 have been studied by Mossbauer spectroucopy from 77.5 up to 650 and 680K, respectively, In the glassy state, the average magnetic hyperfine field decreases with increasing temperature due to a distribution of exchange inter-actions. At low temperatureH(T)/H(0) has a temperature dependence (1 -BT /32 -CT /52) whereB andC are constants, indicative of spin-wave excitations in glassy ferromagnets. The value of B/32) = 0.40 = 0.05 is almost four times larger than those of crystalline iron and nickel. On the other hand, fluctuations of the exchange interaction constant are found to decrease with increasing temperature. The Curie temperaturesT c - 608 K for the glassy Fe81.5B14.5Si4 andT c = 583K for the glassy Fe40Ni40B20 are found to be well defined. AtT close toT c H(T) behaves as a power law with critical exponentβ = 0.3. The crystallizationT cr glassy Fe81.5B14.5Si4 was found to be 645K. The crystalline material obtained contains three different phases, namely α-Fe, Fe2B and Fe-8% Si.

Critical behavior of amorphous ferromagnetic alloys

The results of our systematic magnetization and electrical resistivity measurements on amorphous transition metal-metalloid alloys are reviewed. In the real critical region, the amorphous ferromagnetic alloys (with composition well above the percolation threshold) and crystalline ferromagnets are found to behave alike but outside this temperature region, they exhibit a completely different behavior. These observations are discussed in the light of existing theories and shown to provide a straightforward explanation for a large scatter in the exponent values of glassy ferromagnets found in the literature. For Ni-rich Fe-Ni based glasses, only a small fraction of spins participates in the order-disorder transition. This finding is shown to have an important bearing on the nature of phase transitions in the spin systems with quenched disorder. We present a simple model for the peculiarities observed in the critical behavior of amorphous ferromagnets.