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EuCd2As2 is a remarkably complex magnetic semimetal that may behave as a topological insulator or host two pairs of Weyl points, depending on the growth conditions and the final magnetic state. Both antiferromagnetic (AFM) and ferromagnetic (FM) forms have been grown, and we show here, using 151Eu Mössbauer spectroscopy, that the differences between the AFM and FM forms extend well beyond their ground state magnetic structures. Whereas the AFM form undergoes a conventional AFM → paramagnetic transition on warming, the FM form passes through a complex incommensurate modulated state before becoming paramagnetic. [ABSTRACT FROM AUTHOR]

EuCd2As2 is a remarkably complex magnetic semimetal that may behave as a topological insulator or host two pairs of Weyl points, depending on the growth conditions and the final magnetic state. Both antiferromagnetic (AFM) and ferromagnetic (FM) forms have been grown, and we show here, using 151Eu Mössbauer spectroscopy, that the differences between the AFM and FM forms extend well beyond their ground state magnetic structures. Whereas the AFM form undergoes a conventional AFM → paramagnetic transition on warming, the FM form passes through a complex incommensurate modulated state before becoming paramagnetic. [ABSTRACT FROM AUTHOR]

151Eu Mössbauer spectroscopy has been used to investigate the behaviour of EuAl4 through the four magnetic transitions that occur below 16 K. We find clear evidence for the first transition (TN1, the onset of order) where an incommensurate modulated magnetic structure appears, and the third (TN3) where the modulation disappears at the tetragonal → orthorhombic structural transition. We see no changes at the lowest transition (TN4) but find that the modulation amplitude passes through a maximum at TN2. Data on the isostructural but magnetically simpler EuGa4 are also presented for comparison. [ABSTRACT FROM AUTHOR]

The phase stability and magnetocrystalline anisotropy (MCA) of tetragonal Mn(Al1−xGax) with the L10-type structure (P4/mmm) has been studied using first-principles density functional calculations. The calculated decomposition energy indicates that partial replacement of Al by Ga suppresses the formation of Mn5(Al,Ga)8 and enhances the thermal stability of the L10 phase while the total magnetic moment per formula unit (f.u.) remains almost unchanged. The site- and atomic-resolved MCA calculations show that the MCA energy (MAE) comes mainly from the Mn atoms, and the total MAE increases from 0.25 meV/f.u. (x = 0) to 0.34 meV/f.u (x = 1). Spin resolved MCA and band structure calculations indicate that the high MCA is mainly due to spin flipping behavior near Fermi level. The derived effective magnetic anisotropy field increases from 37 kOe (x = 0) to 46 kOe (x = 1), in agreement with experiments. Doping with Ga improves the thermal stability of the L10 structure and enhances the magnetic anisotropy field, which facilitates developing high coercivity Mn-Al magnets. [ABSTRACT FROM AUTHOR]

The phase stability and magnetocrystalline anisotropy (MCA) of tetragonal Mn(Al1−xGax) with the L10-type structure (P4/mmm) has been studied using first-principles density functional calculations. The calculated decomposition energy indicates that partial replacement of Al by Ga suppresses the formation of Mn5(Al,Ga)8 and enhances the thermal stability of the L10 phase while the total magnetic moment per formula unit (f.u.) remains almost unchanged. The site- and atomic-resolved MCA calculations show that the MCA energy (MAE) comes mainly from the Mn atoms, and the total MAE increases from 0.25 meV/f.u. (x = 0) to 0.34 meV/f.u (x = 1). Spin resolved MCA and band structure calculations indicate that the high MCA is mainly due to spin flipping behavior near Fermi level. The derived effective magnetic anisotropy field increases from 37 kOe (x = 0) to 46 kOe (x = 1), in agreement with experiments. Doping with Ga improves the thermal stability of the L10 structure and enhances the magnetic anisotropy field, which facilitates developing high coercivity Mn-Al magnets. [ABSTRACT FROM AUTHOR]

Earlier Mössbauer investigations of rare earth chromates RCrO4 with R = Gd and Tm were interpreted in terms of a superposition of two sub-spectra (approx. 4:1 area ratio), despite there being only a single crystallographic R(4a) site. In addition, the magnetic transitions exhibited first-order character, which is contrary to bulk magnetic measurements. However, new 161Dy and 166Er Mössbauer data presented here for DyCrO4 and ErCrO4 show the expected single rare earth site in both cases and a conventional second order behaviour for ErCrO4. [ABSTRACT FROM AUTHOR]

In the orthorhombic manganites o-RMnO3, where R is a heavy rare earth (R = Gd-Yb), the Mn3+ sublattice is known to undergo two magnetic transitions. The low temperature phase has an antiferromagnetic structure (collinear or elliptical), which has been well characterized by neutron diffraction in most of these compounds. The intermediate phase, occurring in a narrow temperature range (a few K), is documented for R = Gd–Ho as a collinear modulated structure, incommensurate with the lattice spacings. We report here on a 57Fe Mössbauer study of 2% 57Fe doped o-YbMnO3, where the spin only Fe3+ ion plays the role of a magnetic probe. From the analysis of the shape of the magnetic hyperfine Mössbauer spectra, we show that the magnetic structure of the intermediate phase in o-YbMnO3 (38.0 K < T < 41.5 K) is also modulated and incommensurate. [ABSTRACT FROM AUTHOR]

Neutron powder diffraction measurements complemented by first-principles density functional theory (DFT) calculations have been used to study the irreversible change that accompanies the reversible magnetocaloric transition (MCT) in Mn1.1Fe0.9P0.8Ge0.2. We observe the growth and loss of long-period antiferromagnetism as we pass through the MCT for the first time and the development of significant strain in the cycled material. We attribute both the reversible and irreversible changes to the distance dependence of the Mn-Mn exchange in the Mn-P(Ge) ab-plane layers. [ABSTRACT FROM AUTHOR]

Singular point detection (SPD) for the determination of the anisotropy field (BA) using a conventional magnetometer is demonstrated.We then followthe composition dependence of BA in MnxGa using a combination of SPD measurements complemented by first-principles density functional theory (DFT) calculations. We find excellent quantitative agreement for 1.2 ⩽ x ⩽ 1.8, but observe a marked departure for x ⩽1.2. We suggest that the deviation from ideal behaviour might be associated with site disorder at low excess Mn. [ABSTRACT FROM AUTHOR]

Previously, the bulk magnetisation of polycrystalline DyNiAl4 was found to reach barely half its expected saturation value with a 9 T applied field. New inelastic neutron scattering and 161Dy-Mössbauer spectroscopy results suggest that the crystal field splitting for Dy3+ in DyNiAl4 is dominated by B02 with a low temperature local Dy3+ moment close to its full free-ion value of ± 10 μB. Considering that the magnetization for related single crystal specimens (e.g. for TbNiAl4) typically grows more rapidly with the applied field directed along the easy axis, the slower response for DyNiAl4 powder must be due to a strong magneto-crystalline anisotropy hindering the moment realignment. [ABSTRACT FROM AUTHOR]

We have used neutron powder diffraction to demonstrate the existence of long-range antiferromagnetic order of Ising-like Dy moments in the DyCd6 quasicrystal approximant phase. This cubic compound undergoes a slight distortion to a monoclinic cell at low temperatures. The Néel temperature is 18.0(2) K and the magnetic order of the Dy sublattice may be described in the parent cubic I m 3 ¯ structure using a combination of two propagation vectors, k1 = [0 0 0] and k 2 = [ 1 2 0 1 2 ] , yielding 'anti-I' order. Alternatively, when referred to the monoclinic C2/c cell, the magnetic structure may be described by a single propagation vector: k = [1 0 0]. [ABSTRACT FROM AUTHOR]

We have used neutron powder diffraction to demonstrate the existence of long-range antiferromagnetic order of Ising-like Dy moments in the DyCd6 quasicrystal approximant phase. This cubic compound undergoes a slight distortion to a monoclinic cell at low temperatures. The Néel temperature is 18.0(2) K and the magnetic order of the Dy sublattice may be described in the parent cubic I m 3 ¯ structure using a combination of two propagation vectors, k1 = [0 0 0] and k 2 = [ 1 2 0 1 2 ] , yielding 'anti-I' order. Alternatively, when referred to the monoclinic C2/c cell, the magnetic structure may be described by a single propagation vector: k = [1 0 0]. [ABSTRACT FROM AUTHOR]

Room temperature neutron powder diffraction has been used to investigate the chemical structure and magnetic ordering of a series of tetragonal (I4/mmm #139) MnxGa (1.15 ≤ x ≤ 2.0) alloys. Initially (x < 1.5) the excess Mn goes on the 2b site with vacancies appearing at the 2a site. For x > 1.5 Mn also appears on the 2a site. The manganese atoms on the 4d site carry an almost constant moment of 2.16(6) μB/Mn. The loss of magnetisation seen with increasing Mn content is shown to be the result of large (~ 3 μB/Mn), antiparallel Mn moments on the 2b, and later 2a sites, and not to a reduction of the Mn moment on the 4d sites. [ABSTRACT FROM AUTHOR]

155Gd Mössbauer spectroscopy and neutron powder diffraction have been used to study magnetic ordering in Gd5Ir2Bi and Gd5Ir2Sb. Despite the hyperfine fields (Bhf) at the two Gd sites differing by more than a factor of two for both compounds, the moments derived from neutron diffraction are essentially equal in Gd5Ir2Bi. This implies an unusual departure from the commonly assumed scaling between BhfGd and μGd. Neutron powder diffraction shows that Gd5Ir2Bi is a c-axis ferromagnet at 3.6 K. We find no evidence for a FM→AF transition. [ABSTRACT FROM AUTHOR]

Earlier Mössbauer investigations of rare earth chromates RCrO4 with R = Gd and Tm were interpreted in terms of a superposition of two sub-spectra (approx. 4:1 area ratio), despite there being only a single crystallographic R(4a) site. In addition, the magnetic transitions exhibited first-order character, which is contrary to bulk magnetic measurements. However, new 161Dy and 166Er Mössbauer data presented here for DyCrO4 and ErCrO4 show the expected single rare earth site in both cases and a conventional second order behaviour for ErCrO4. [ABSTRACT FROM AUTHOR]

Previously, the bulk magnetisation of polycrystalline DyNiAl4 was found to reach barely half its expected saturation value with a 9 T applied field. New inelastic neutron scattering and 161Dy-Mössbauer spectroscopy results suggest that the crystal field splitting for Dy3+ in DyNiAl4 is dominated by B02 with a low temperature local Dy3+ moment close to its full free-ion value of ± 10 μB. Considering that the magnetization for related single crystal specimens (e.g. for TbNiAl4) typically grows more rapidly with the applied field directed along the easy axis, the slower response for DyNiAl4 powder must be due to a strong magneto-crystalline anisotropy hindering the moment realignment. [ABSTRACT FROM AUTHOR]