Magnetic Anisotropy Constant K1 Research Articles

Dielectric and temperature dependent magnetic studies of Al3+ substituted Ba0.4La0.1Sr0.5AlxFe12-xO19 hexaferrite for microwave application

The Al3+ substituted polycrystalline Ba0.4La0.1Sr0.5AlxFe12-xO19 (0 ≤ x ≤ 1) hexaferrite sample were prepared by the solid-state method. The structural, morphology, dielectric, and temperature dependent magnetic properties are studied systematically. The XRD and Rietveld refinement analysis revealed that all the samples have magneto plumbite hexaferrite structure with space group P6/mmc. The lattice parameters a and c are decreased from 5.888 Å to 5.874 Å and 23.109 Å to 23.085 Å, respectively. The c/a ratio is found to be between 3.92 and 3.93, which is ideal for M−type hexaferrite. It is observed that all the Raman peaks are shifted along the higher wavenumber with increasing Al3+ substitution. The surface morphology of these samples has uniform grain sizes and is closely packed. Also, all the constituent elements are present in proper composition except barium, which has a little higher atomic percentage than the calculated value. The complex dielectric constant (ε', ε“) decreased with Al3+ insertion (for x = 0: ε' = 3.44 k, ε” = 0.993 k; x = 1: ε' = 0.744 k, ε“ = 0.211 k @ 1 MHz). The hysteresis isotherm curves were analyzed by the law of approach to saturation magnetization in the temperature range of 10 K − 300 K. Further, the saturation magnetization and magnetic anisotropy constant K1(T) are found to be decreased, whereas anisotropy field Ha(T) and coercivity HC(T) are rises with an increase in temperature as well as Al3+ concentration. The Bloch’s spin wave theory is used to analyze temperature dependent saturation magnetization, and all the samples get deviated from Bloch’s T3/2 law as well as modified Kobler’s Bloch law. It might be due to finite size effects, long wavelength excitation, and the introduction of constant energy gap into spin wave spectrum, geometrical asymmetries, and other atomic disorders. Finally, Dyson’s approximation which includes T5/2 terms is perfectly fitted with the experimental data. The analysis makes it possible to predict the curie temperature and visualize the nature of the ferromagnetic coupling with the increasing Al3+ concentrations. Above that, the temperature dependent magnetic anisotropy constant K1(T) is linearly fitted with cubic of temperature dependent saturation magnetization MS(T), which confirmed that all the samples have uniaxial hexagonal crystal symmetry. The combination of magnetic and dielectric responses made the material suitable for permanent magnets and microwave applications.

Influence of La-Nb co-substituted Sr ferrite on microstructure, spectrum and magnetic properties of hexaferrites

The M-type Sr hexaferrites with nominal compositions Sr1−xLaxNbxFe12−xO19(x = 0.00, 0.04, 0.08, 0.12, 0.16, 0.20) were fabricated by solid-state reaction method. The microstructure and magnetic properties of hexaferrites were characterized by X-ray diffraction (XRD), Fourier transformer infrared (FTIR) spectroscopy, filed emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometer (VSM). The regular changes of microstructure and magnetic properties were studied at 1300 °C by doping quantity. XRD results show that the substitution of La-Nb is successful when x < 0.16, and α-Fe2O3 begins to appear when x > 0.16; FT-IR shows that there are frequency bands of tetrahedral and octahedral Fe‒O at 613 cm−1 and 451 cm−1, which proves the formation of lattice and structure of M-type Sr1−xLaxNbxFe12−xO19 hexagonal ferrite respectively; The SEM micrographs are regular hexagonal block with tight arrangement and obvious layering. EDS indicates that all elements are predetermined and no other elements are produced. VSM shows that the sample obtains high saturation magnetization (Ms), and increases slightly with the increase of doping amount. The coercivity (Hc) first increases with Nd-Nb Zn content (x) from 0.00 to 0.04, and then decreases when Nd-Nb Zn content x > 0.08; the value of SQR, magnetic crystal anisotropy constant (k1) and magnetic anisotropy field (Ha) decrease with the increase of doping amount, and the number of magnetons (nB) is consistent with the saturation magnetization (Ms). In this paper, for the first time we have studied the mechanism of La-Nb co-substituted which will lead to the change of ferrite morphology and properties at high temperature.

Role of low substrate temperature deposition on Co–Fe thin films

This paper presents the role of the conventional and Soliton wave model deposition at low substrate temperature (300–100 K) on the structural, electric and magnetic properties of Co35Fe65 thin films deposited by thermal evaporation using bulk polycrystalline Co35Fe65 alloy. On account of obtaining superior quality magnetic thin films without any high temperature growth processes or heat treatment, the Soliton wave growth model at suitable low temperature range is used. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques are employed to investigate the various structural properties. Morphological and structural analyses of entire 30 nm Co35Fe65 thin films deposited on Si (100) substrate reveal that the stoichiometry is preserved over the whole temperature deposition and BCC crystalline formed with (110) texture. To attain the electrical and magnetic properties, resistivity and vibrating-sample magnetometer (VSM) measurements are evaluated. Soliton wave model deposition significantly increased magnetic anisotropy constant K1 = 0.105 Merg/cm3, MR/MS = 0.83 and coercivity HC = 272 Oe at 300 K when the compared to conventional deposition range in this work (K1 = 0.014 Merg/cm3, MR/MS = 0.6 and HC = 50 Oe). Growth with novel approach of Co35Fe65 thin films highlights the reasonable low coercivity, the high saturation magnetization, the high magnetic anisotropy and the low electrical resistivity values, with tailored grain size, make them feasible to use in magnetic sensor technology in the near future.

Magnetic anisotropy constants of ThMn12-type Sm(Fe1–xCox)12 compounds and their temperature dependence

The first and second-order uniaxial magnetic anisotropy constants K1 and K2 of the Sm(Fe1–xCox)12 compounds and their temperature dependence are determined by the torque magnetometry technique using the anomalous Hall effect (AHE) on epitaxially grown Sm(Fe1-xCox)12 thin films. While K1 monotonically decreases with increasing temperature regardless of the Co concentration, K2 changes its sign from negative to positive with increasing temperature and reaches a maximum at 250 K. These observations are consistent with the hard-axis magnetization curves at low temperature that show an upward deviation from a linear extrapolation of the low field part. Ab-initio estimations of the crystal field parameters at the Sm site using a spin model of Sm(Fe1–xCox)12 compounds and theoretical analysis of magnetocrystalline anisotropy of Sm3+ ions taking the multiple J-mixing into account explain these main features of the experimental results.

Evolution of frozen magnetic state in co-precipitated ZnδCo1−δFe2O4 (0 ≤ δ ≤ 1) ferrite nanopowders

The evolution of frozen magnetic state of ZnδCo1−δFe2O4 (0 ≤ δ ≤ 1) ferrite nanoparticles was studied by applying vibrating sample magnetometer measurements in temperature range 5–350 K and magnetic fields up to 7 T. It was shown that gradual conversion from the inverse spinel (δ = 0) to the normal one (δ = 1.0) is correlated with a drop of freezing temperature Tf (corresponding to blocking of mean magnetic moment of the system) from 238 K (δ = 0) to 9 K (δ = 1.0) and with a decrease of magnetic anisotropy constant K1 from about 8 · 105 J/m3 to about 3 · 105 J/m3. The percolation threshold predicted for bulk ferrites at 1 − δ ≈ 0.33 was observed as a significant weakness of ferrimagnetic coupling. In this case magnetization curves, determined according to the zero field cooling protocol, reveal two distinct maxima indicating that the system splits into two assemblies with specific ions distribution between A and B sites.

Random Magnetic Anisotropy Studies in SmCo5 Thin Films

SmCo5 thin films with different thicknesses were prepared by electron beam evaporation on Kapton substrates. The out-of-plane hysteresis loops for different thicknesses reveal a maximum coercive field when the thickness is 15 nm. Using random magnetic anisotropy model, the thickness dependence of magnetic properties was studied in SmCo5 nanocrystalline films and several fundamental magnetic parameters were extracted. We have determined the local magnetic anisotropy constant K 1 which is found to increase with increasing film thickness except for t = 7 nm which is thought to arise from the structural imperfection of the SmCo5 films.

Compositional dependence of magnetic anisotropy in chemically synthesized Co3−xFexO4 (0 ≤ x ≤ 2)

Magnetic anisotropy of Co3−xFexO4 (CFO, 0 ≤ x ≤ 2) thin-film and powder samples prepared by a sol–gel method has been investigated as a function of Fe composition x. Structural analyses by X-ray diffraction show that CFO powder samples exhibit diffraction peaks associated with the spinel structure when x < 2, while CFO thin-film samples with thickness of 130–510 nm yield the peaks when 0 ≤ x ≤ 2. CFO thin-film samples are highly (111)-oriented with the Lotgering factor greater than 0.9 when 0.6 ≤ x ≤ 1.3. The magnetic anisotropy constant K1 of CFO powder samples estimated from their room-temperature hysteresis loops yields a minimum when x = 0.9. Relatively large in-plane magnetic anisotropy (Keff = 5.7 × 105 erg/cm3) is observed for the CFO thin-film sample when x = 1.3. With increasing x, the magnetic easy axis of the spinel CFO changes from 〈111〉 to 〈100〉 when x = 0.9.

Random magnetic anisotropy studies in nanocrystalline Pr2Co7Hx (0 ≤ x ≤ 3.75) hydrides

We investigate the effect of hydrogen insertion on the microstructure and magnetic properties of nanocrystalline Pr2Co7Hx (0 ≤ x ≤ 3.75) hydrides. The Pr2Co7Hx hydrides were characterized by X-ray diffraction (XRD) and physical properties measurement system (PPMS9) Quantum Design. Mean field theory was used to describe the temperature dependence of magnetization and deduce the exchange interactions and Curie temperature. We also apply the approach to saturation magnetization to our system. The results were interpreted in the framework of random magnetic anisotropy model. From such analysis, some fundamental parameters were extracted. We have determined the local magnetic anisotropy constant K1 which is found to increase from 5.2 × 107 erg/cm3 to a maximum of 5.7 × 107 erg/cm3 with increasing x from 0 to 2.5, respectively. This confirms the hypothesis of the electronic and magnetovolume effect of hydrogen insertion. In addition, it is shown that Herzer theory describes satisfactory the experimental data of change of coercive field as a function of grain size.

Effect of the Mn/Fe Ratio on the Microstructure and Magnetic Properties in the Powder Form (Fe1−x Mn x )2P System

The structure, morphology, and magnetic properties of the mechanically alloyed iron manganese phosphides (Fe1−xMnx)2P with 0.15 ≤ x ≤ 0.75 (Mn/Fe ratio = 0.17, 0.33, 0.66, and 3) have been studied by means of X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, and BS1 and BS2 magnetometry. The powder form (Fe1−xMnx)2P compounds exhibit multiphase structures that contain Fe(Mn)-type solid solution and Fe2P-type, Mn2P-type, Fe3P-type, and MnP/FeP-type phosphides. The magnetization versus temperature reveals the existence of multiple magnetic phase transitions. The saturation magnetization, coercivity, and squarness Mr/Ms ratio values are discussed as a function of both the Mn content and the temperature. From the approach to saturation magnetization studies, several fundamental magnetic parameters were extracted. The local magnetic anisotropy constant K1 was determined.

Selective tuning of magnetization dynamics damping in Tb- and Nd-doped permalloy ultrathin films by adjacent copper nanolayers

The mechanism of angular dependence of ferromagnetic resonance linewidth of dilute Tb and Nd doping in permalloy thin films with various thicknesses of adjacent copper layer are investigated by experimental approach and theoretical fitting by considering the contributions from intrinsic spin-orbit coupling, inhomogeneous broadening and two-magnon scattering. The results show that the damping coefficient α, by intrinsic contribution extracted from ferromagnetic resonance linewidth, increases from 0.0153 to 0.0218 for NiFe–Nd films and from 0.0193 to 0.0261 for NiFe–Tb films resulting from the spin pumping effect at the interface of NiFe–Nd(or Tb)/Cu as the thickness of copper layer increases from 1 nm to 15 nm. The surface magnetic anisotropy constant K1 is obtained and shows an decreasing trend from positive to negative, which implies that the copper layer could reduce the surface perpendicular anisotropy. The fitting spin mixed conductivity is (2.72±0.18)×1015 cm−2 at NiFe–Tb/Cu interface and (2.4±0.2)×1015 cm−2 at Cu/NiFe–Nd interface, respectively.

Temperature dependence of multi-jump magnetic switching process in epitaxial Fe/MgO (001) films**Project supported by the National Basic Research Program of China (Grant Nos. 2015CB921403, 2011CB921801, and 2012CB933102) and the National Natural Science Foundation of China (Grant Nos. 51427801, 11374350, and 11274361).

Temperature dependence of magnetic switching processes with multiple jumps in Fe/MgO (001) films is investigated by magnetoresistance measurements. When the temperature decreases from 300 K to 80 K, the measured three-jump hysteresis loops turn into two-jump loops. The temperature dependence of the fourfold in-plane magnetic anisotropy constant K1, domain wall pinning energy, and an additional uniaxial magnetic anisotropy constant KU are responsible for this transformation. The strengths of K1 and domain wall pinning energy increase with decreasing temperature, but KU remains unchanged. Moreover, magnetization reversal mechanisms, with either two successive or two separate 90° domain wall propagation, are introduced to explain the multi-jump magnetic switching process in epitaxial Fe/MgO(001) films at different temperatures.

Crystal field parameters with Wannier functions: application to Nd2Fe14B systems

A new method to calculate the crystal field parameters (CFPs) is first applied to crystalline Nd2Fe14B as the representative of rare-earth iron boron permanent magnets. The CFPs are extracted from the one electron Hamiltonian expressed in the basis of Wannier functions. The low energy properties of 4f orbitals and influence of hybridization with Fe(3d) orbitals are investigated by solving the eigenvalue problems. Authors have found the fundamental property; the more the 4f electron cloud is expanded to the a–b plane, the more the single-ion anisotropy along the c-axis increases. The magnetic anisotropy constant K1 increases as taking into account the hybridization with Fe(3d) states. The results for CFPs are compared with previous theoretical and experimental studies.

Theoretical evaluation of the temperature dependence of magnetic anisotropy constants of Nd2Fe14B: Effects of exchange field and crystal field strength

To identify the possible mechanism of the coercivity (Hc) degradation of Nd–Fe–B sintered magnets, we study the roles of the exchange field acting on the 4f electrons in Nd ions and theoretically investigate how variation in the exchange field affects the values of the magnetic anisotropy constants K1 and K2. We find that, with decreasing exchange field strength, both values decrease as a result of the lower asphericity of the 4f electron cloud, indicating that the local anisotropy constants might become small around the grain boundaries, where the exchange fields are reduced owing to the smaller coordination number.

Fabrication and magnetocrystalline anisotropy of NiCo(002) films**Project supported by the National Natural Science Foundation of China (Grant Nos. 11374227, 51331004, 51171129, and 51201114) and the Shanghai Science and Technology Committee, China (Grant Nos. 0252nm004, 13XD1403700, and 13520722700).

A series of 30-nm-thick epitaxial NixCo1-x (002) alloy films are fabricated by DC magnetron sputtering. MgO (002) and SrTiO3 (002) single substrates are used for x>0.5 and x<0.5, respectively. The magnetocrystalline anisotropy of NixCo1-x (002) alloy films is studied in the entire composition region for 0≤ x≤ 1.0. When x decreases, the cubic magnetic anisotropy constant K1 changes sign from negative to positive at x=0.96 and becomes negative again at x= 0.79. It becomes more negative as x decreases from 0.79 to 0. The uniaxial anisotropy Ku is smaller than the K1 by a factor of two orders.

Angular dependence of ferromagnetic resonance in Tb-doped Ni80Fe20 thin films

The mechanisms of angular dependence of ferromagnetic resonance (FMR) linewidth of dilute Tb doping in Ni80Fe20 thin films are investigated by experimental approach and the theoretical fitting by considering the contributions from intrinsic spin–orbit coupling, two-magnon scattering and inhomogeneous broadening. It is shown that the damping coefficient α, by intrinsic contribution extracted from FMR linewidth, is increased by more than 50 times as the Tb concentration increases to 8.4%, indicating that the spin–orbit coupling of this system increases with the introduction of Tb impurities. The magnetic anisotropy constants K1 and K2 are obtained and show an increasing trend from negative to positive, which implies that the Tb dopants could enhance the perpendicular anisotropy.

Structure and magnetism of dilute Co(Zr) nanoclusters

Co(Zr) nanoclusters having a small fraction of Zr (≤7.8 at. %) were produced using a cluster-deposition method and aligned using a magnetic field of about 5 kOe prior to deposition. This study shows that Zr addition to Co nanoclusters improves the fraction of hexagonal close-packed structure, magnetic anisotropy, and easy-axis alignment process. Co(Zr) nanoclusters having 7.8 at. % of Zr exhibit a considerably enhanced magnetic anisotropy constant K1 ≈ 6.7 Mergs/cm3 and coercivity Hc ≈ 700 Oe at 300 K as compared to those of Co nanoclusters (K1 ≈ 2.9 Mergs/cm3 and Hc ≈180 Oe).

Magnetic properties of ultrathin single crystal Fe3O4 film on InAs(100) by ferromagnetic resonance

The evolution of both in-plane and out-of-plane magnetic anisotropies has been studied on different thicknesses of Fe3O4/InAs(100) hybrid spintronic structures by ferromagnetic resonance. The uniaxial magnetic anisotropy with easy axis along InAs [011] direction and hard axis along [0-11] direction and the cubic magnetic anisotropy are determined by fitting the resonance field. The cubic magnetic anisotropy constant K1 is negative, as that of bulk magnetite, and its absolute value increases rapidly from 0.2 × 104 erg/cm3 to 10.8 × 104 erg/cm3 with increasing thickness of Fe3O4 film. When the thickness of Fe3O4 film is only several monolayers (tFe = 6 nm), a bulk-like cubic magneto-crystalline anisotropy is built up. The uniaxial anisotropy constant is much smaller than that in Fe3O4/GaAs film with the same thickness of Fe3O4 film, as expected from the less lattice mismatch at the interface.

Magnetism of cluster-deposited Y–Co nanoparticles

Nanoparticles of YCo2, YCo3, and YCo5 are produced by cluster-deposition and investigated bothstructurally and magnetically. The nanoparticles have sizes of less than 10 nm and aresuperparamagnetic at 300 K, irrespective of stoichiometry. As-produced nanoparticles exhibitdisordered structures with magnetic properties differing from those of the bulk particles.The temperature-dependent magnetization curves of the nanoparticles reveal blocking temperatures from 110 to 250 K, depending on stoichiometry. The magnetic anisotropy constant K1 of disordered YCo5 nanoparticles of 7.8 nm in size is 3.5 × 106 ergs/cm3, higher than those of thedisordered YCo2 (8.9 × 105 ergs/cm3) and YCo3 (1.0 × 106 ergs/cm3) nanoparticles.

Phase composition and magnetic properties of nanocrystalline SmFe11 − x Ga x C1.25 (2 ≤ x ≤ 5) alloys

As-cast and rapidly quenched alloys (RQAs) SmFe11 − xGaxC1.25 (2 ≤ x ≤ 5) have been studied. The RQAs were prepared by melt spinning on a steel wheel rotating at a velocity V = 10−40 m/s. Fragments of the RQAs were annealed in a vacuum at Tann = 500−850°C. The as-cast alloys are multiphase; the maximum volume fraction in them corresponds to the Sm2(Fe, Ga)17C compound with a rhombohedral structure. The rapid quenching leads to the formation of the Sm(Fe, Ga)11C compound (1: 11) with a tetragonal BaCd11-type structure; the maximum volume fraction of the compound is reached in the alloy with x = 3 quenched to a wheel rotating at V = 30 m/s. The melt spinnins of the alloys with x = 2−4 at V = 40 m/s is accompanied by their substantial amorphization. During annealing, the amorphous phase crystallizes mainly with the formation of the 1: 11 phase. A nonequilibrium phase diagram of the alloys quenched at V = 40 m/s and annealed at Tann = 500−850°C has been constructed. The 1: 11 compound has a single-phase region near x = 3 at Tann ≥ 600°C. As the volume fraction of the 1:11 phase increases, the coercive force Hc of nanocrystalline RQAs increases. The maximum coercive force is observed for the SmFe8Ga3C1.25 alloy quenched at V = 40m/s and subsequently annealed at 700°C; it is 0.8 and 12 kOe at 293 and 50 K, respectively. The high coercive force obtained indicates that the Sm(Fe, Ga)11C phase is magnetically uniaxial and has a high magnetic anisotropy energy. The magnetic anisotropy constant K1 of the compound at T = 50 K was estimated to be 3.1 × 107 erg/cm3.

Some Properties of Co-Ni-(Mn, Y, Cr) Spinel Fine Particles With Giant Coercivity Synthesized by Chemical Coprecipitation Method

This experiment was carried out to investigate magnetic and physical properties of Co-Ni-(Mn, Y, Cr) spinel fine particles prepared by the chemical coprecipitation method and subsequently eliminating the superparamagnetic ultraflne particles by etching treatment with the diluted sulfuric acid. It was found that the coercivity of these fine particles were obtained over 880 kA/m, in particular Co-Ni-Cr spinel fine particles obtained coercivity exceeding 1.6 MA/m. We obtained magnetic anisotropy constants K1, K2, and the anisotropy field HA known to be huge.