Ho Moments Research Articles

Density functional theory and Monte Carlo simulation insights into electronic structure and magnetic properties in HoSi and CeSi

The electronic and magnetic properties of heavy fermion bulk CeSi and HoSi were studied using density functional theory (DFT) and Monte Carlo simulation (MCS). The exchange correlation (XC) potential was solved by GGA (generalized gradient approximation), TB-mBJ (Tran Blaha modified Becke Johnson) approximations, and also by TB-mBJ and GGA combined with U (Hubbard parameter). Calculations of the electronic structure indicate that CeSi and HoSi compounds are metals and reveal antiferromagnetic behavior. However, the calculations within the TB-mBJ+U approach predict ferrimagnetic behavior for HoSi. The magnetic moments of Ce and Ho in HoSi and CeSi have been estimated. The values of N é el temperature, TN, are found to be 6.61 K and 22.5 K for CeSi and HoSi, respectively. The theoretical TN value of CeSi is very close to that found experimentally, 6.1 K. The maximum of susceptibility is investigated for both compounds.

Effect of Ho Substitution on Magnetic Properties and Microstructure of Nanocrystalline Nd-Pr-Fe-B Alloys

The inevitable thermal demagnetization of magnets at high-temperatures is a key issue for Nd-Fe-B based permanent magnetic materials, especially for electric motors. Here, we report the effect of partially substituting the element Holmium (Ho) on the magnetic properties and microstructure of nanocrystalline melt-spun [(NdPr)1−xHox]14.3Fe76.9B5.9M2.9 (x = 0–0.6; M = Co, Cu, Al and Ga) alloys. It shows that Ho can enter into the main phase and significantly enhance the coercivity (Hcj). A large coercivity of 23.9 kOe is achieved in the x = 0.3 alloy, and the remanent magnetization (Mr) remains in balance. The abnormal elevated temperature behavior of Mr is observed in the alloys with a high amount of Ho substitution, in which the Mr of the x = 0.6 alloy increases with rising temperature from 300 K to 375 K owing to the antiparallel coupling between Ho and Fe moments. As a result, the positive value (0.050%/K) of temperature coefficient α of Mr is achieved in the x = 0.6 alloy within the temperature range of 300–400 K, in excess of that of existing Nd-Fe-B magnets. The temperature coefficient β of Hcj is also improved by Ho substitution, indicating the introduction of Ho in Nd-Fe-B magnets is beneficial for thermal stability. The microstructure observation of x = 0, 0.3 and 0.6 alloys confirmed the grain refinement by Ho substitution, and Ho prefers to remain in the 2:14:1 phase than Nd and Pr. The present finding provides an important reference for the efficient improvement of the thermal stability of Nd-Fe-B-type materials.

Phase precipitation and properties of melt-spun Ho-Fe-B alloys prepared by direct quenching and over-quenching followed by heat treatment

Aiming to fully utilize rare earth (RE) resources and develop new high coercivity magnets, the magnetic properties and phase precipitation behavior of Ho-Fe-B alloys were systematically studied. The Ho12+xFe82-xB6 (x = −2, −1, 0, 1, 2) alloys were prepared by melt spinning at various wheel speeds. For the directly quenched Ho12Fe82B6 alloy, the optimum magnetic properties can be obtained at a wheel speed of 22 m/s with the coercivity Hcj = 1.07 × 103 kA/m, remanence Jr = 0.45 T and maximum energy product (BH)max = 36.6 kJ/m3 due to its single Ho2Fe14B phase structure. A maximum Hcj = 2.95 × 103 kA/m can also be obtained at 100 K due to the temperature dependence of anisotropy field and existence of spin reorientation of Ho2Fe14B compound. Jr decreases with decreasing temperature owing to the antiparallel coupling between Ho and Fe moments. The increase of Ho content can enhance the coercivity but deteriorate the remanence. More than 2 at. % reduction of Ho leads to the formation of soft magnetic Ho2Fe17 phase and greatly reduces the coercivity, which is different from many other RE-Fe-B alloys. The phase precipitation behavior of over-quenched amorphous Ho12+xFe82-xB6 alloys during heat treatment were also studied, and the precipitation of Ho2Fe14B phase is confirmed in all alloys. Ho2Fe17 phase precipitates in the Ho10Fe84B6 alloy at the temperature of 882.7 K. The magnetic properties of over-quenched Ho12+xFe82-xB6 alloys after optimally annealed are similar to the directly quenched alloys. In addition, the corrosion resistance of the directly quenched alloys was also investigated. The present results provide reference for developing highly stable RE-Fe-B based magnets with alternative RE resource.

Negative Magnetization and Exchange Bias Behavior in Nanocrystalline Ho2CoMn1−xNixO6 (x=0‐0.4) Double Perovskite

A gel combustion method is opted to prepare nanocrystalline samples of Ho2CoMn1−xNixO6 (x = 0–0.4) (HCMNO) double perovskite. Structural studies reveal a formation of nanocrystalline samples, which crystallize into monoclinic structure with space group P21/n. A drop in the lattice parameters including unit cell volume are noticed with Ni substitution. Magnetization versus temperature (M-T) analysis shows a single FM transition in the parent compound at 83 K (TC1) and it is ascribed to the super exchange interaction in Co2+ - O2- - Mn4+ networks. However, it is turned into two FM transitions (TC1, TC2) after Ni substitution, where TC2 arises due to possible super exchange interaction in Co2+ - O2- - Ni4+ networks. The transition temperature TC1, is decreasing from 83 to 76 K for x = 0.0–0.4 sample, whereas TC2 increases up to 88 K for x = 0.4 sample. A magnetization reversal (MR) has been observed in higher Ni concentration (x = 0.3 and 0.4) samples in the field cooled state with a compensation temperature (Tcomp) of 4.4 K and 10 K respectively. This MR is attributed to the competition between the ferromagnetic (FM) moment of the transition metal (TM) ions and the polarization of magnetic moments of rare-earth (RE) ions at low temperatures. A typical bipolar switching of magnetization has been demonstrated for x = 0.3 and 0.4 sample. At 5 K, the hysteresis (M-H) loops demonstrate a decrease in saturation magnetization (MS) and coercivity (Hc) value after Ni substitution. However, the observed MS of the order of 11.60–10.27 µB/f.u. (for x = 0.0–0.4) at 5 K is attributed to some visible contribution related to the polarization/ordering of Ho moment with the net magnetic moment of TM ions. A maximum exchange bias field value of 230 Oe has been observed at 5 K for x = 0.4 sample. It is due to the competition between the spin canted magnetic moments of RE ions and the FM moments of TM ions.

Magnetic properties and noncollinear spin structure of the tin-rich stannide Ho5Co6Sn18

We have investigated the magnetic, structural, and thermodynamic properties of ${\mathrm{Ho}}_{5}{\mathrm{Co}}_{6}{\mathrm{Sn}}_{18}$ through x-ray and neutron diffraction, magnetization, and specific heat measurements. ${\mathrm{Ho}}_{5}{\mathrm{Co}}_{6}{\mathrm{Sn}}_{18}$ displays a magnetic transition at ${T}_{M}=3.4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and can be described with the magnetic space group $I{4}_{1}/a{c}^{\ensuremath{'}}{d}^{\ensuremath{'}}$. The two holmium sublattices Ho(1) and Ho(2) exhibit different magnetic behaviors. Ferromagnetic order on the Ho(1) site develops into a net magnetization along the $c$ axis below ${T}_{M}$. In contrast, the ordering of the Ho(2) site is determined by geometric magnetic frustrations. The Ho(2) spins order into the noncollinear, two-in-two-out antiferromagnetic pattern on the $\mathrm{Ho}{(2)}_{4}$ tetrahedron. At 60 mK, the ordered moment of Ho(2) reaches $4.01\phantom{\rule{0.16em}{0ex}}(8)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$, which is about half of the Ho(1) moment. Upon the application of a magnetic field, ferromagnetic components along the $c$ axis are induced on Ho(2), along with the in-plane antiferromagnetic components, indicating the XY-like spin anisotropy of the Ho(2) spins. A magnetic quasielastic neutron scattering signal is observed above ${T}_{M}$ and significantly weakens with the magnetic ordering.

Spin reorientation behaviour and dielectric properties of Fe-doped h-HoMnO3

We have studied the magnetic structure, spin reorientation behaviour and dielectric properties of polycrystalline HoMn1−x Fe x O3 (0.0 ⩽ x ⩽ 0.25) compounds using magnetization, neutron diffraction and dielectric measurements. These compounds crystallize predominantly in the hexagonal phase (P63 cm) with a small phase fraction of the orthorhombic phase (Pnma) which increases with increase in dopant concentration and a total suppression of the hexagonal phase is observed at x = 0.25. Doping Fe at the Mn site leads to an increase in the spin reorientation temperature (T SR) from 33 K (x = 0) to 55 K (x = 0.1) while the T N remains nearly constant at 72 K. The magnetic structure of the hexagonal phase was found to be Γ4 (P63′c′m) below T N and Γ3 (P63′cm′) below T SR. The magnetic ordering temperature of Ho3+ ions at 2(a) site appears to coincide with the T SR only in the case of x = 0 sample. The Ho ions at 4(b) site are found to magnetically order below 8 K. The T N of the Ho ions at both 4(b) and 2(a) sites do not appear to be affected by doping at the Mn site. The temperature variation of the Mn and Ho moments follow the Brillioun function dependence albeit with differing values of the molecular field constant λ 0 and λ 1. Short range magnetic order alone was found for the completely orthorhombic sample (x = 0.25). An anomalous suppression of the dielectric constant (ε) at T N is observed in the case of hexagonal samples. Further, a linear correlation between Δε (= ε(T) − ε(0)) and the square of the antiferromagnetic moment M, is observed in these compounds.

Hollow Bimetallic Complex Nanoparticles for Trimodality Imaging and Photodynamic Therapy In Vivo.

Hollow nanoparticles have received an enormous amount of attention in the field of nanomedicine. Herein, water-soluble hollow bimetallic complex nanoparticles, holmium(III)/iridium(III) bimetallic complex nanoparticles (Ir-Ho HNPs), were fabricated via a coordination assembly. Owing to the special metal-to-ligand charge transfer (MLCT) and the heavy-atom effect of Ir(III) in an iridium complex, Ir-Ho HNPs exhibited an intense phosphorescence and the generation of singlet oxygen (1O2). With the long electron relaxation time and high magnetic moment of Ho(III), Ir-Ho HNPs presented a high longitudinal relaxivity (r2) value (160.0 mM-1 s-1at 7.0 T). Their unique hollow structure resulted in their strong and stable ultrasound signal in an aqueous solution. As a proof of concept, Ir-Ho HNPs have been developed for the phosphorescence imaging and photodynamic therapy for living cells, ultrasound imaging, and high-field magnetic resonance imaging in vivo. Our work opened up an avenue for novel application of an iridium complex in cancer theranostics.

New DyHoCo medium entropy amorphous microwires of large magnetic entropy change

Abstract We report upon the excellent magnetocaloric effect in melt-extracted DyHoCo medium entropy microwires. The magnetic entropy change (-ΔSM) reaches a large value of ∼11.2 J kg−1 K−1 for a field change (μ0ΔH) of 5 T. The large value of -ΔSM is resulted from the large magnetic moments of Dy and Ho. In addition, the DyHoCo microwires show a good cooling efficiency; RC1, RC2 and RC3 are evaluated to be ∼530 J kg−1, ∼417 J kg−1 and ∼279 J kg−1, respectively, at μ0ΔH = 5 T. The DyHoCo microwires undergo a second-order paramagnetic-ferromagnetic transition at the Curie temperature of ∼35 K. The excellent magnetocaloric property makes the melt-extracted DyHoCo microwires a promising refrigerant for cryogenic cooling application.

Magnetic frustration in a metallic fcc lattice

Magnetic frustration in metals is scarce and hard to pinpoint, but exciting due to the possibility of the emergence of fascinating novel phases. The cubic intermetallic compound HoInCu$_4$ with all holmium atoms on an fcc lattice, exhibits partial magnetic frustration, yielding a ground state where half of the Ho moments remain without long-range order, as evidenced by our neutron scattering experiments. The substitution of In with Cd results in HoCdCu$_4$ in a full breakdown of magnetic frustration. Consequently we found a fully ordered magnetic structure in our neutron diffraction experiments. These findings are in agreement with the local energy scales and crystal electric field excitations, which we determined from specific heat and inelastic neutron scattering data. The electronic density of states for the itinerant bands acts as tuning parameter for the ratio between nearest-neighbor and next-nearest-neighbor interactions and thus for magnetic frustration.

Neutron Diffraction Study of Unusual Magnetic Behaviors in the Ho2Fe11Al6 Intermetallic Compound.

Knowledge of structure-property relationships is fundamental but significant in the exploitation of magnetic materials. Here we report that the high Al substitution for Fe transformed the crystal structure from a hexagonal Ho2Fe17 compound to a rhombohedral Ho2Fe11Al6 compound. Intriguingly, the latter shows unusual evolution of magnetization around 86 and 220 K compared with the former. Integrated investigations of the detailed structure analysis and magnetic performance on the Ho2Fe11Al6 compound demonstrate that the Ho2Fe11Al6 compound possesses a stable rhombohedral structure (R3̅m) from 5 to 430 K with preferred occupation of Al atoms and ferrimagnetic structure in which the magnetic moments of Ho and Fe lie antiparallel in the basal plane below the Curie temperature. The results of the temperature dependence of moments reveal that the disparate rates of change of the moments for Ho and Fe sublattices give rise to unusual evolution of magnetization around 86 and 220 K and then turn to paramagnetic above 280 K. This work provides clear structure and magnetization information on the Ho2Fe11Al6 compound, which may be beneficial to guiding the future development of magnetic materials.

Microscopic Nature of the First-Order Field-Induced Phase Transition in the Strongly Anisotropic Ferrimagnet HoFe_{5}Al_{7}.

We report on x-ray magnetic circular dichroism experiments in pulsed fields up to 30T to follow the rotations of individual magnetic moments through the field-induced phase transition in the ferrimagnet HoFe_{5}Al_{7}. Near the ground state, we observe simultaneous stepwise rotations of the Ho and Fe moments and explain them using a two-sublattice model for an anisotropic ferrimagnet with weak intersublattice exchange interactions. Near the compensation point, we find two phase transitions. The additional magnetization jump reflects the fact that the Ho moment is no longer rigid as the applied field acts against the intersublattice exchange field.

Magnetic and magnetodielectric behavior of the Haldane spin-chain system, Ho2BaNiO5

The Haldane spin-chain compound, Ho2BaNiO5, crystallizing in an orthorhombic space group (Immm) and known to order antiferromagnetically below (TN=) 53 K, is investigated by magnetization, heat-capacity, dielectric, magnetodielectric, and pyrocurrent studies as well as neutron diffraction experiments down to 2 K. We report here another magnetic feature in the close vicinity of 12 K (as a consequence of the saturation of the magnetic moment of Ho) as revealed by qualitative changes in the behavior of isothermal magnetization when the temperature is varied across 12–15 K. Heat-capacity and magnetic susceptibility data also are consistent with this conclusion. The compound can be classified as ‘metamagnetodielectric’, when comparing the plots of dielectric constant as a function of temperature and magnetic field with the corresponding plots of magnetization. We are not able to find any evidence for ferroelectricity. This is notable considering that all the heavy rare-earth members of this family with the same crystal structure were known to be multiferroics. Pyrocurrent data however reveal a feature around 55 K, which is attributable to ‘thermally stimulated depolarization current’.

Pressure dependence of the magnetic properties and phase diagram of HoCo12B6 ferrimagnetic compound

Abstract The magnetic properties of HoCo12B6 ferrimagnetic compound are investigated versus the magnetic field, temperature and pressure. The magnetic phase diagram exhibits three remarkable temperatures: the ordering temperature TC, the spin reorientation temperature TSR and the compensation temperature TCOMP at 147 K, 76 K and 47 K respectively. In HoCo12B6 intermetallic system the spontaneous magnetization resulting from the antiparallel coupling of the magnetic moments of Ho and Co sublattices is pressure insensitive at lowest temperatures whereas it decreases with pressure at temperature range above TSR. The mean Co magnetic moment is small (

Quasielastic and low-energy inelastic neutron scattering study of HoCrO3 by high resolution time-of-flight neutron spectroscopy

In order to understand the origin of the huge quasielastic magnetic scattering observed previously with a back-scattering neutron spectrometer, we have re-investigated the low energy excitations in HoCrO3 by inelastic neutron scattering in a much wider energy range with time-of-flight neutron spectrometers. The inelastic signals are due to the excitations between the ground state doublet of the Ho ion. The quasielastic signal is due to the fluctuation of the disordered Ho moments. At low temperature the intensity of quasielastic scattering is small. It starts increasing as the temperature increases above 30 K. At the same temperature, the elastic intensity due to Ho moment ordering decreases in a similar way. This observation strengthens the hypothesis that the quasielastic scattering is due the fluctuations of the disordered Ho moments. The time scale of fluctuations has been determine from the quasielastic scattering and was found to vary from about 22 ps at K to about 2.5 ps at K. The stretched exponential line shape indicates a distribution of decay rates at low temperatures.

A neutron diffraction study of the hexagonal Laves phases, Ho(Co0.667Ga0.333)2 and Er(Co0.667Ga0.333)2: Co/Ga site preferences and magnetic structure

RE(Co0.667Ga0.333)2 (RE = Ho, Er) were characterized by neutron powder diffraction (NPD). Rietveld refinement of the NPD data at 280K confirms the hexagonal MgZn2-type structure (P63/mmc), in accordance with the previous XRD results. Co/Ga occupancies on the 2a and 6h sites were refined to be 0.46/0.54(2) and 0.74/0.26(2), respectively, indicating a preference of Ga for the 2a site and of Co for the 6h site. Both materials are ferromagnetic, k = (000), with measureable moments only on the RE sites. The magnetic (Shubnikov) space group is P63/mm′c′ for the Er phase. Co moments refined to values of 0.1–0.3 μB and are effectively zero within 3σ. The Er moment, 6.07(8) μB at 3.5K is parallel to the c axis and this orientation persists up to TC = 18.5K, while the Ho moment has components along both the a and c axes with a total moment of 6.3(1) μB at 3.5K. Both moments are much reduced from the free ion values, 9 μB (Er) and 10 μB (Ho), which is attributed to crystal field effects. In addition, the Ho moment angle with the c axis is strongly temperature dependent, being roughly constant, ~ 24(6)° from T = 29K to ~25K, then increasing with decreasing temperature to 44(1)° at 3.5K. Magnetic small angle neutron scattering (MSANS) was observed over a Q-range from 0.14Å−1 to 0.50Å−1 in both samples. The integrated MSANS of the Er phase peaks near TC, then decreases monotonically with decreasing temperature, behavior typical for a simple ferromagnet. On the other hand, the integrated MSANS for the Ho phase exhibits a weak peak around TC = 31K, followed by a plateau to 25K and a strong increase with decreasing temperatures, which tracks the evolution of the Ho moment angle with the c axis.

Single crystal polarized neutron diffraction study of the magnetic structure of HoFeO3

Polarised neutron diffraction measurements have been made on HoFeO3 single crystals magnetised in both the [0 0 1] and [1 0 0] directions (Pbnm setting). The polarisation dependencies of Bragg reflection intensities were measured both with a high field of T parallel to [0 0 1] at K and with the lower field T parallel to [1 0 0] at K. A Fourier projection of magnetization induced parallel to [0 0 1], made using the hk0 reflections measured in 9 T, indicates that almost all of it is due to alignment of Ho moments. Further analysis of the asymmetries of general reflections in these data showed that although, at 70 K, 9 T applied parallel to [0 0 1] hardly perturbs the antiferromagnetic order of the Fe sublattices, it induces significant antiferromagnetic order of the Ho sublattices in the plane, with the antiferromagnetic components of moment having the same order of magnitude as the induced ferromagnetic ones. Strong intensity asymmetries measured in the low temperature structure with a lower field, 0.5 T [1 0 0] allowed the variation of the ordered components of the Ho and Fe moments to be followed. Their absolute orientations, in the domain stabilised by the field were determined relative to the distorted perovskite structure. This relationship fixes the sign of the Dzyalshinski–Moriya (D-M) interaction which leads to the weak ferromagnetism. Our results indicate that the combination of strong y-axis anisotropy of the Ho moments and Ho-Fe exchange interactions breaks the centrosymmetry of the structure and could lead to ferroelectric polarization.

Role of the rare earth in lattice and magnetic coupling in multiferroic h−HoMnO3

We used Raman scattering to study the lattice and magnetic excitations in the hexagonal HoMnO3 single crystals. The E2 phonon mode at 237 cm-1 is affected by the magnetic order. This mode is related to the displacement of Mn and O ions in a-b plane and modulates the Mn-O-Mn bond angles in a-b plane and the in-plane Mn-Mn superexchange interaction. The mode at 269 cm-1 associated to the displacement of the apical Ho3+ ions along the c direction presents an abrupt change of slope at TN showing that the role of the rare earth ions can not be neglected in the magnetic transition. We have identified magnon and crystal field excitations. The temperature dependence of the magnetic excitations has been compared to the Mn and Ho moment and indicates that the exchange interaction pattern between Mn and Ho atoms drives the uniaxial anisotropy gap above the Mn-spin-rotation transition.

Temperature evolution of magnetic structure of HoFeO3 by single crystal neutron diffraction

We have investigated the temperature evolution of the magnetic structures of HoFeO3 by single crystal neutron diffraction. The three different magnetic structures werevfound as a function of temperature for HoFeO3. In all three phases the fundamental coupling between the Fe sub-lattices remains the same and only their orientation and the degree of canting away from the ideal axial direction varies. The magnetic polarisation of the Ho sub-lattices in these two higher temperature regions, in which the major components of the Fe moment lie along x and y, is very small. The canting of the moments from the axial directions is attributed to the antisymmetric interactions allowed by the crystal symmetry. In the low temperature phase two further structural transitions are apparent in which the spontaneous magnetisation changes sign with respect to the underlying antiferromagnetic configuration. In this temperature range the antisymmetric exchange energy varies rapidly as the the Ho sub-lattices begin to order. So long as the ordered Ho moments are small the antisymmetric exchange is due only to Fe-Fe interactions, but as the degree of Ho order increases the Fe-Ho interactions take over whilst at the lowest temperatures, when the Ho moments approach saturation the Ho-Ho interactions dominate. The reversals of the spontaneous magnetisation found in this study suggest that in HoFeO3 the sums of the Fe-Fe and Ho-Ho antisymmetric interactions have the same sign as one another, but that of the Ho-Fe terms is opposite.

Density-functional study of the structures and properties of holmium-doped silicon clusters HoSi n (n = 3-9) and their anions.

The structures and properties of Ho-doped Si clusters, including their adiabatic electron affinities (AEAs), simulated photoelectron spectra (PESs), stabilities, magnetic moments, and charge-transfer characteristics, were systematically investigated using four density-functional methods. The results show that the double-hybrid functional (which includes an MP2 correlation component) can accurately predict the ground-state structure and properties of Ho-doped Si clusters. The ground-state structures of HoSi n (n = 3-9) are sextuplet electronic states. The structures of these Ho-doped Si clusters (aside from HoSi7) are substitutional. The ground-state structures of HoSi n- are quintuplet electronic states. Their predicted AEAs are in excellent agreement with the experimental ones. The mean absolute error in the theoretical AEAs of HoSi n (n = 4-9) is only 0.04eV. The simulated PESs for HoSi n- (n = 5-9) are in good agreement with the experimental PESs. Based on its simulated PES and theoretical AEA, we reassigned the experimental PES of HoSi4- and obtained an experimental AEA of 2.2 ± 0.1eV. The dissociation energies of Ho from HoSi n and HoSi n- (n = 3-9) were evaluated to test the relative stabilities of the clusters. HOMO-LUMO gap analysis indicated that doping the Si clusters with the rare-earth metal atom significantly increases their photochemical reactivity. Natural population analysis showed that the magnetic moments of HoSi n (n = 3-9) and their anions derive mainly from the Ho atom. It was also found that the magnetic moments of Ho in the HoSi n clusters are larger than the magnetic moment of an isolated Ho atom.

Cycloid spirals and cycloid cone transition in the HoMn6−xCrxGe6 (T, x) magnetic phase diagramm by neutron diffraction

The structures and magnetic properties of the antiferromagnetic hexagonal pseudo ternary compounds HoMn6−xCrxGe6 (x=1, 1.5 and 2) are studied by neutron diffraction in the temperature range 1.5–300K. The substitution of nonmagnetic Cr for Mn greatly affects the magnetic properties of HoMn6Ge6 by reducing the ordering temperature from 466K to 278K, 205K and 130K for (x=0, 1, 1.5 and 2) respectively, increasing the c/a ratio, suppressing the high temperature (HT) commensurate phase with q2=(0, 0, 1/2) and changing the high temperature (LT) q1=(0, 0, q1z) skew spiral rotation plane.HoMn5CrGe6 and HoMn4Cr2Ge6 display in the entire magnetically ordered regime cycloid spiral structures with the wave vector: q=(0, 0, qz), qz≈0.18(3) r.l.u. and Φs≈64.8° turn angle. The Ho and Mn/Cr (001) layers have ferromagnetic arrangements coupled antiferromagnetically. The Ho moments in the z=0 layer are oriented in a direction opposite to the line bisecting the angle 2φMn≈2×28° of the Mn layers at z=±∼0.25. This triple unit changes orientation collectively in the direction of q within the (b, c) plane containing the wave vector. Above 50K, the wave vector length increases linearly from 0.24 to 0.28(1) r.l.u. below TN.The HT HoMn4.5Cr1.5Ge6 cycloid spiral, is stable in the range Tt<T<TN (q1=(0, 0, q1z), q1z=0.1711(3) r.l.u., Φs =61.6° at 40K). At variance to the other compounds, crossing Tt≈36K from above, it undergoes a first order magnetoelastic transition from a cycloid HT q1 to a LT longitudinal cone structure: q2=(0, 0, q2z), q2z=0.149r.l.u., Φs=53.6° and cone angle ΦC=47°. The q1 and q2 phases coexist in the LT range down to 1.5K≤T≤Tt in varying amounts with T. This transition is directly manifested by the splitting of the HT magnetic satellites and the increase of characteristic nuclear intensities. The results are summarised in a (T, x) magnetic phase diagram.