Easy Magnetization Direction Changes Research Articles

2D high temperature ferromagnetic Co2Ti2Sn2 monolayer with tunable magnetic anisotropy and superior mechanical flexibility: A first-principles and Monte Carlo study

A novel type of two-dimensional (2D) alloy Co2Ti2Sn2 with intrinsic ferromagnetism have been predicted using first-principles calculations. The results show that Co2Ti2Sn2 monolayer exhibits a considerably large magnetic anisotropic energy (MAE) of 533 μeV per Co2Ti2Sn2 formula and the MAE can be tuned by carrier doping. For the electron doping, the MAE increases monotonically and significantly enhances ~60% up to 866 μeV, while for the hole doping, MAE decreases from positive to negative at the critical point of - 4 × 1014 cm−2, corresponding to the change of easy magnetization direction from out-of-plane to in-plane. In addition, Monte Carlo simulations based on classical Heisenberg model estimate a high Curie temperature of approximate 463 K. Besides, we show that the Co2Ti2Sn2 monolayer possesses good mechanical flexibility and can withstand a strain ranging from −32% to 22% and −15%–10% under uniaxial and biaxial direction, respectively. With the uniaxial stretching strain up to 12.4%, a magnetic phase transition will occur, during which the magnetic moment jumps to zero accompanied by energy jumping. Similar phenomenon is also observed at −6.5% and −8.8% under biaxial and uniaxial compression, respectively. These explored controllable magnetic properties, electronic properties, superior mechanical flexibility and the high Curie temperature render the 2D Co2Ti2Sn2 monolayer a promising candidate for applications in magnetic logic device and nanospintronic applications.

Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1)

We study crystal structure, phase transitions and magnetism of pseudo-binary TmxDy1-xAl2 (0 ≤ x ≤ 1) compounds using temperature dependent X-ray powder diffraction, specific heat and magnetization measurements, first principles, and model calculations. In low external magnetic fields, Dy-rich compounds undergo continuous, second-order phase transitions at the respective Curie temperatures, TC. In contrast, the Tm-rich compounds exhibit discontinuous, first-order anomalies in the magnetically ordered states. These sharp transitions correlate with a substantial energy difference between the room temperature cubic and ground state rhombohedral structures of TmAl2. A clear anomaly in the lattice parameter is observed at ∼30 K for x = 0.5, which nearly coincides with TC = 31.2 K. The effective quadrupolar moment of the lanthanides changes sign around x = 0.5, which leads to a nearly zero anisotropy constant and approximately spherical effective 4f charge densities, providing an explanation for the lack of structural distortions below TC for x = 0.5. The calculations confirm [001] as the easy magnetization axis in the ground state tetragonal structure of DyAl2, and reveal collapse of the orbital magnetic moment when the easy magnetization direction changes to [111]. Within the rhombohedral ground state of TmAl2 [111] is the easy magnetization direction.

Preparation and properties of pure crystalline perovskite CeFeO3 thin films with vanadium doping

AbstractCerium ferrite (CeFeO3) thin films doped with vanadium (V:CeFeO3) were grown on SiO2 quartz glass and <100>‐oriented SrTiO3 (STO) crystal substrates by the radio‐frequency magnetron sputtering method in this study. The effects of crystallization, substrate, and V‐doping on the quality, the magnetic property and the magneto‐optical property of as‐prepared films are investigated. V:CeFeO3 film grown on STO substrate has better crystallinity and has better lattice integrity due to the higher lattice matching between substrate and film. The magnetic hysteresis loop and the magnetic circular dichroism spectra show that the magnetization strength and the magneto‐optical properties of V:CeFeO3 films have the significant anisotropy. Moreover, V‐doping and the stress lead to the change in easy magnetization direction of film. It shows that the perovskite B‐site doping with transition‐metal ion has significant influence on the magnetic and the magneto‐optical properties of CeFeO3 thin films.

Uranium ferromagnet with negligible magnetocrystalline anisotropy:U4Ru7Ge6

Strong magnetocrystalline anisotropy is a well-known property of uranium compounds. The almost isotropic ferromagnetism in $\mathrm{U_{4}Ru_{7}Ge_{6}}$ reported in this paper represents a striking exception. We present results of magnetization, AC susceptibility, thermal expansion, specific heat and electrical resistivity measurements performed on a $\mathrm{U_{4}Ru_{7}Ge_{6}}$ single crystal at various temperatures and magnetic fields and discuss them in conjunction with results of first-principles electronic-structure calculations. $\mathrm{U_{4}Ru_{7}Ge_{6}}$ behaves as an itinerant 5$f$-electron ferromagnet ($T_{\mathrm{C}}= 10.7 K$, $\mu_{\mathrm{S}}= 0.85 \mu_{\mathrm{B}}/f.u.$ at 1.9 K. The ground-state easy-magnetization direction is along the [111] axis of the cubic lattice. The anisotropy field $\mu_{0}H_{\mathrm{a}}$ along the [001] direction is only of $\sim0.3 T$, which is at least 3 orders of magnitude smaller value than in other U ferromagnets. At $T_{r}=5.9 K$ the easy magnetization direction changes for [001] which holds at temperatures up to $T_{\mathrm{C}}$. The magnetoelastic interaction induces a rhombohedral (tetragonal) distortion of the paramagnetic cubic crystal lattice in case of the [111]([001]) easy-magnetization direction. The rhombohedral distortion is connected with two crystallographically inequivalent U sites. The ab initio calculated ground-state magnetic moment of $1.01 \mu_{\mathrm{B}}/f.u.$ is oriented along [111]. The two crystallographically inequivalent U sites are a consequence of spin-orbit coupling of the U 5$f$-electrons. In the excited state which is only 0.9 meV above the ground state the moment points to the [001] direction in agreement with experiment.

Magnetostriction and anisotropy compensation in TbxDy0.9−xNd0.1Fe1.93 [0.2≤x≤0.4

Structure and magnetostriction of TbxDy0.9−xNd0.1Fe1.93 (0.2≤x≤0.4) compounds are investigated. All the compounds are found to stabilize in MgCu2-type C15 cubic Laves phase structure. The easy magnetization direction changes from ⟨100⟩(x=0.2) to ⟨111⟩(x=0.3) through an intermediate state at x=0.25. Anisotropy compensation is realized near x=0.25 for the TbxDy0.9−xNd0.1Fe1.93 compounds. The Laves phase compound Tb0.4Dy0.5Nd0.1Fe1.93 has large spontaneous magnetostriction (1670×10−6) and a low anisotropy at room temperature which could make it a good candidate material for magnetostriction applications.

The effect of substrate on magnetic properties of Co/Cu multilayer nanowire arrays

Ordered Co/Cu multilayer nanowire arrays have been fabricated into anodic aluminium oxide templates with Ag and Cu substrate by direct current electrodeposition. This paper studies the morphology, structure and magnetic properties by transmission electron microscopy, selective area electron diffraction, x-ray diffraction, and vibrating sample magnetometer. X-ray diffraction patterns reveal that both as-deposited nanowire arrays films exhibit face-centred cubic structure. Magnetic measurements indicate that the easy magnetization direction of Co/Cu multilayer nanowire arrays films on Ag substrate is perpendicular to the long axis of nanowire, whereas the easy magnetization direction of the sample with Cu substrate is parallel to the long axis of nanowire. The change of easy magnetization direction attributed to different substrates, and the magnetic properties of the nanowire arrays are discussed.

Change of easy magnetization direction in TmMn 6Sn 6− xGa x (0.00 < x < 1.22) studied in high magnetic fields

Single crystals of TmMn 6Sn 6− x Ga x compounds (0 ≤ x ≤ 1.22) obtained in a tin flux have been studied by thermomagnetic and high-field magnetization measurements. A collinear-antiferro to heli-magnetic transition at 324 K has been observed in TmMn 6Sn 6. Spin-reorientation transitions at low temperature are found in the compounds with x = 0.66 and 1.22. The magnetization curves in high fields at 4.2 K are interpreted to result from the competition between the Tm–Mn exchange interaction and the magnetocrystalline anisotropy of the Tm and Mn sublattices. A strong easy-plane anisotropy is favored for the Ga-poor compounds and a strong easy-axis anisotropy for the Ga-rich compounds while the compounds of intermediate Ga content (0.51 ≤ x ≤ 0.66) display rather weak magnetocrystalline anisotropy.

Temperature Dependence of Magnetic Moment Orientation in Co2Z-Type Hexaferrite Estimated by High-Temperature Neutron Diffraction

We investigated the correlation between the thermomagnetic curve of Co2Z-type hexagonal barium ferrite and its magnetic moment direction. We measured the thermomagnetic curve of Ba3Co1.8Fe24.2O41, prepared using the conventional solid-state reaction method, in the temperature range from 294 to 773 K with a vibrating sample magnetometer under 70 Oe. The curve shows two significant magnetization slumps at 540 K and 680 K. High-temperature XRD patterns show that no crystal transformation occurs in the temperature region from 294 to 773 K. High-temperature neutron diffraction experiments were performed to investigate the magnetic moment orientation at elevated temperatures. The Rietveld analyses of the neutron diffraction patterns indicate that the temperature rise from 523 to 573 K makes the magnetic moments turn to the c-axis from a direction parallel to the c-plane most significantly. The slump in magnetization at 540 K may be attributed to the change in easy magnetization direction from the c-plane to the c-axis. The change in average orientation of the magnetic moments must be induced by the disappearance of the contribution of cobalt to magnetism in this temperature range.

Structure and magnetocrystalline anisotropy of (Nd 1−xY x) 3Fe 29−yCr y compounds

Structure and magnetic properties of (Nd 1− x Y x ) 3Fe 29− y Cr y compounds with x = 0 – 1.0 and y = 4 – 1.5 have been investigated. It is found that in an adequate annealing temperature range all the investigated compounds crystallize in the Nd 3(Fe,Ti) 29-type structure. However when the annealing temperature is below 1323 K, the Y 3Fe 27.5Cr 1.5 compound crystallizes in a disordered CaCu 5-type structure. Substitution of Y for Nd leads to a reduction of the lattice parameters. The Curie temperature T c shows no clear change as the Y and Cr contents change in the above-mentioned concentration region. With increasing Y content, the easy magnetization direction changes from close to the [0 4 0] direction to the [4 0 −2] direction. The X-ray-diffraction patterns and the AC susceptibility of the (Nd 1− x Y x ) 3Fe 29− y Cr y samples reveal a spin reorientation phenomenon for x = 0 – 0.4 as the temperature decreases from room temperature to 77 K. The spin reorientation temperature T sr increases monotonically with increasing Y content from 158 K for x = 0 to 201 K for x = 0.4 .

Structural and magnetic properties of (Nd xR 1−x) 3Fe 24Cr 5 (R=Gd and Tb) intermetallic compounds

The crystal structure and magnetic properties of (Nd x R 1− x ) 3Fe 24Cr 5 (R=Gd and Tb) compounds with x = 0.0 – 0.8 have been investigated by means of X-ray diffraction and magnetic measurements. All the samples are single phase and crystallize in the Nd 3(Fe,Ti) 29-type structure with space group A2/m. As the Nd content increases, the lattice parameters a, b, c and the unit-cell volume V increase in both the (Nd x Gd 1− x ) 3Fe 24Cr 5 and the (Nd x Tb 1− x ) 3Fe 24Cr 5 compounds due to the lanthanide contraction. The room-temperature easy magnetization direction changes to the [0 4 0] direction with increasing Nd content. The Curie temperature of (Nd x Gd 1− x ) 3Fe 24Cr 5 decreases monotonically upon substitution of Nd for Gd, while the Curie temperature of the (Nd x Tb 1− x ) 3Fe 24Cr 5 compounds decreases with the Nd content for x = 0 – 0.4 and increases for x = 0.4 – 0.8 . The saturation magnetization M S increases monotonically with increasing Nd content for both compound systems and can be described in terms of a simple dilution model.

Magnetic properties ofSm3Fe28.1−xCoxMo0.9(x=0,4,8,12,14,16)compounds

~Received 17 April 2003; revised manuscript received 22 December 2003; published 27 May 2004! A series of Sm3Fe28.12xCoxMo0.9 compounds (x50,4,8,12,14,16) have been synthesized and their magnetic properties and structures investigated by means of x-ray diffraction and magnetic measurements. It is found that substitution of Co for Fe leads to a significant increase of the Curie temperature and saturation magnetization. Even more important, for x>14 the easy magnetization direction changes from easy plane to easy axis. In this compound system, Sm3Fe12.1Co16Mo0.9 is a very promising candidate for rare-earth permanent magnetic materials. Its room temperature saturation magnetization ( m 0Ms51.50 T) and anisotropy field (Ba56.5 T) are comparable to those of Nd2Fe14 B( m 0Ms51.60 T and Ba57.0 T). However, its Curie temperature is 1020 K, which is substantially higher than that of Nd 2Fe14 B( TC5588 K). The lattice inversion method has been employed to calculate the site occupancies of Mo and Co in the quaternary 3:29 type Sm3Fe282xCoxMo compounds (x50, 4, 8, 12, 16!. The results show that Co preferentially occupies Fe1, Fe8, and Fe11 sites, whereas Mo occupies Fe3, Fe2, and Fe6 sites. As Co atoms preferentially occupy Fe1, Fe8, and Fe11 sites, the negative exchange interactions of Fe-Fe pairs associated with the sites are modified into positive and strong interactions of Fe-Co or Co-Co, which leads to the rise of Curie temperature. The bond lengths between various atoms obtained by computer simulation are used to calculate the Curie temperatures of Sm3Fe292xMox (x50 and 1!. The calculated Curie temperature of Sm3Fe28Mo is close to the experimental value.

Sm 3 (Fe,Co,Mo) 29 compounds: promising materials for permanent magnets

The outstanding hard-magnetic properties are reported of Sm3Fe28.1-xCoxMo0.9 compounds with x=12, 14, 16. In this alloy system, only a small amount of Mo is needed to stabilize the 3:29 structure so that the magnetic properties are not seriously affected by the presence of this nonmagnetic element. Substitution of Co for Fe leads to a significant increase of the magnetic anisotropy, and for x greater than or equal to 14 the easy magnetization direction changes from easy plane to the easy axis. In this alloy system, the compound Sm3Fe12.1Co16Mo0.9 is a very promising candidate for permanent magnet applications. Its room temperature saturation magnetization (mu(0)M(s)=1.5T) and anisotropy field (B-an=6.5 T) are comparable to the values for Nd2Fe14B (mu(0)M(s)=1.6 T and B-an=7 T). However, the Curie temperature of Sm3Fe12.1Co16Mo0.9 is 1020 K, which is appreciably higher than that for Nd2Fe14B (T-C=588 K).

Magnetic properties of TbMn 6 Sn 6- x Ga x ( x =0.0-1.2) compounds

Effects of Ga substitution for Sn on the structure and magnetic properties of TbMn6Sn6-xGax (x=0.0-1.2) compounds have been investigated by means of x-ray diffraction, magnetization measurement and 119Sn Mössbauer spectroscopy. The substitution of Ga for Sn results in a decrease in lattice constants and unit-cell volumes. The magnetic ordering temperature decreases monotonically with increasing Ga content from 423 K for x=0.0 to 390 K for x=1.2. At room temperature, the easy magnetization direction changes from the c-axis to the ab-plane. This variation implies that the substitution of Ga for Sn leads to a decrease in thec-axis anisotropy of the Tb sublattice. An increase in the non-magnetic Ga concentration results in a monotonic decrease of the spontaneous magnetization Ms at room temperature. Since there are three non-equivalent Sn sites, 2c (0.33, 0.67,0), 2d (0.33, 0.67,0.5) and 2e (0,0,0.34) in the TbMn6Sn6-xGax compounds, the 119Sn Mössbauer spectra of the TbMn6Sn6 and TbMn6Sn5.4Ga0.6 compounds can be fitted by three sextets. The hyperfine fields (HFs) decrease in the order of HF(2d)>HF(2e)>HF(2c), which is in agreement with the magnetic structure.

Structure and magnetic properties of TbMn/sub 6/Sn/sub 6-x/Ti/sub x/ (x=0-0.9) compounds

The effects of Ti substitution for Sn on the structure and magnetic properties of TbMn/sub 6/Sn/sub 6-x/Ti/sub x/ (x=0-0.9) compounds have been investigated by means of X-ray diffraction (XRD), magnetization measurements and /sup 119/Sn Mossbauer spectroscopy. The substitution of Ti for Sn results in an increase in the lattice constants and the unit-cell volumes. The magnetic ordering temperature decreases monotonically with increasing Ti content from 423 K for x=0 to 376 K for x=0.9. At room temperature, the easy magnetization direction changes from the c-axis for x HF(2e)>HP(2c), which is in agreement with the magnetic structure.

Nano-composite SmFe 7C x/α-Fe permanent magnet

The structure, phase transformation and magnetic properties of the Sm 19Fe 67C 14 alloy prepared by mechanical alloying (MA) and subsequent re-milling have been studied systematically. With increasing re-milling time, the magnetic main phase, Sm 2Fe 14C (Nd 2Fe 14B-type structure), changes via a metastable SmFe 7C x phase (TbCu 7-type structure) to Sm-carbide (NaCl-type structure). Consequently, the easy magnetization direction changes from the basal phase for Sm 2Fe 14C to the c-axis for SmFe 7C x . The optimal values of M r/ M s=0.81 and ( BH) max=6.8 MGOe have been achieved for nano-composite SmFe 7C x /α-Fe permanent magnet.

Syntheses and magnetic properties of Nd/sub 3/Co/sub 13-x/Ni/sub x/B/sub 2/ borides

The effect of substitution of Ni for Co in the borides Nd/sub 3/(Co/sub 13-x/Ni/sub x/)B/sub 2/ (x=0, 1, 2, 3, 4, 5) on the crystal structure and magnetic properties has been investigated. The lattice parameter a decreases while c increases with increasing x in the range 0/spl les/x/spl les/5. The Curie temperature and saturation magnetic moment per formula unit in Nd/sub 3/(Co/sub 13-x/Ni/sub x/)B/sub 2/ decrease monotonically as the Ni concentration increases. We have observed spin-reorientation transitions at temperatures that decrease monotonically with increasing Ni concentration. It is noteworthy that the substitution of Ni has a significant effect on the magnetocrystalline anisotropy of the Co sublattice, leading to the change of easy magnetization direction of Nd/sub 3/(Co/sub 13-x/Ni/sub x/)B/sub 2/ compounds from basal plane to the c axis at room temperature when x/spl ges/2. The magnetic phase diagram of the Nd/sub 3/(Co/sub 13-x/Ni/sub x/)B/sub 2/ borides is given, and the behavior of magnetocrystalline anisotropy is analyzed by the single ion model.

Magnetic anisotropy evolution of (Ce,Y) 2Co 17 compounds

The evolution of the magnetic anisotropy of (Ce,Y) 2Co 17 compounds with increasing Ce concentration was investigated by magnetic measurements and X-ray diffraction on magnetically aligned powders. At room temperature the easy magnetization direction changes from perpendicular to the c-axis to parallel to the c-axis with increasing Ce concentration. A spin-reorientation transition from easy-axis anisotropy at higher temperatures to easy-plane anisotropy at lower temperatures arises at about 600, 530 and 320 K in Ce 1.3Y 0.7Co 17, Ce 1.5Y 0.5Co 17 and Ce 1.7Y 0.3Co 17, respectively. The Curie temperature and spontaneous magnetization decrease with increasing Ce concentration. These magnetic behaviours are discussed in terms of the itinerant 4f states of Ce ion and the hybridization between the cobalt 3d states and the cerium 4f states.

Magnetic properties of R 2Fe 17− xGa xC (R=Gd or Tb) compounds

The effect of Ga substitution on the structure and magnetic properties of R 2Fe 17C (R=Gd or Tb) compounds has been investigated by X-ray diffraction (XRD) and magnetization measurements. Samples were prepared by arc-melting. XRD patterns indicate that all samples have a rhombohedral Th 2Zn 17-type structure, except for R 2Fe 9Ga 8C (R=Gd, Tb), which contains a small amount of an impurity phase. The unit cell volume v is found to increase monotonically with increasing the Ga concentration at a rate of 7.1 Å 3 for Gd 2Fe 17C and 6.2 Å 3 for Tb 2Fe 17C per Ga atom. The Curie temperature T c shows a maximum value at about x=3 and a minimum value at about x=6 for both Gd 2Fe 17− x Ga x C and Tb 2Fe 17− x Ga x C compounds. X-ray diffraction measurements on magnetically aligned powder samples reveal a change in easy magnetization direction.

Magnetic properties and structure of the intermetallic compounds

The effect of substitution of Fe for Co in the compounds (x = 0.0-0.5) on the crystal structure and magnetic properties has been investigated. The lattice parameters and the unit-cell volume of increase with x in the range . The magnetic moment per formula unit in increases linearly as the Fe concentration increases. The Curie temperature is found to increase for and then decrease for x > 0.1. The easy-magnetization direction changes from the easy-axis direction to the easy-plane direction (x = 0.4), and the anisotropy field decreases with the Fe substitution. Evidence for spin reorientation in the compounds for was observed in the M-T and curves.

Magnetic anisotropy of RCo 10Si 2 compounds (R = Y, Gd, Dy, Ho, Er, Tm)

The magnetic anisotropy of RCo 10Si 2 compounds has been studied in the temperature range from 4.2 to 300 K by means of AC-susceptibility and magnetization measurements. GdCo 10Si 2 does not form and crystallizes in the 1:11 phase which has a very low Curie temperature compared with the 1:12 compounds. The anisotropy field of YCo 10Si 2 decreases with increasing temperature. All 1:12 compounds investigated show easy-plane anisotropy at room temperature. In DyCo 10Si 2 and HoCo 10Si 2, spin-reorientation transitions occur at 190 and 75 K, respectively, where the anisotropy changes to easy-axis type. In ErCo 10Si 2, at 70 K, the easy-magnetization direction changes from basal plane to cone.