High-frequency Electron Paramagnetic Resonance Research Articles

Engineering Clock Transitions in Molecular Lanthanide Complexes.

Molecular lanthanide (Ln) complexes are promising candidates for the development of next-generation quantum technologies. High-symmetry structures incorporating integer spin Ln ions can give rise to well-isolated crystal field quasi-doublet ground states, i.e., quantum two-level systems that may serve as the basis for magnetic qubits. Recent work has shown that symmetry lowering of the coordination environment around the Ln ion can produce an avoided crossing or clock transition within the ground doublet, leading to significantly enhanced coherence. Here, we employ single-crystal high-frequency electron paramagnetic resonance spectroscopy and high-level ab initio calculations to carry out a detailed investigation of the nine-coordinate complexes, [HoIIIL1L2], where L1 = 1,4,7,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraaza-cyclododecane and L2 = F- (1) or [MeCN]0 (2). The pseudo-4-fold symmetry imposed by the neutral organic ligand scaffold (L1) and the apical anionic fluoride ion generates a strong axial anisotropy with an mJ = ±8 ground-state quasi-doublet in 1, where mJ denotes the projection of the J = 8 spin-orbital moment onto the ∼C4 axis. Meanwhile, off-diagonal crystal field interactions give rise to a giant 116.4 ± 1.0 GHz clock transition within this doublet. We then demonstrate targeted crystal field engineering of the clock transition by replacing F- with neutral MeCN (2), resulting in an increase in the clock transition frequency by a factor of 2.2. The experimental results are in broad agreement with quantum chemical calculations. This tunability is highly desirable because decoherence caused by second-order sensitivity to magnetic noise scales inversely with the clock transition frequency.

Magneto-optical and high-frequency electron paramagnetic resonance spectroscopy of Er3+ ions in CaMoO4 single crystal

We present the optical and magneto-optical spectroscopy and electron paramagnetic resonance (EPR) investigations of CaMoO4 single crystals doped with the erbium ions. Telecom-wavelength resonance transition inhomogeneous line width of Er3+ is relatively narrow for oxide crystals which makes this material promising for quantum technologies applications. The hyperfine structure in optical spectra of 167Er3+ isotope is well resolved. Energies and symmetries of wavefunctions of 39 energy levels of Er3+ ions in the crystal-field (CF) of S4 symmetry and g-factors of some CF Kramers doublets were measured and successfully simulated on the basis of CF calculations. The obtained set of CF parameters was used for modeling the hyperfine structure profiles observed in the optical absorption spectra.

Room temperature coherence properties and 14N nuclear spin readout of NV centers in 4H–SiC

We have investigated the room temperature spin coherence properties of the axial NVkk center in 4H–SiC by pulsed high-frequency electron spin resonance and electron-nuclear double resonance techniques. Our results show a remarkable phase coherence time (TCoherence) of 25.3 μs at room temperature for ensembles of NV centers. We demonstrate precise control over NV defect spins through Rabi oscillations, which exhibit a linear response to microwave power. Additionally, the demonstrated room temperature readout of the intrinsic 14N nuclear spin (I = 1) underscores its potential as a robust nuclear spin memory resource, further positioning NV defects in 4H–SiC as an advanced platform for implementing cutting-edge quantum technologies in semiconductor systems.

Evidence of ferromagnetic coupling for manganese pairs in a layered van der Waals GaS semiconductor

Using high-frequency electron paramagnetic resonance (EPR), we have observed the ferromagnetic coupling of manganese Mn2+ pairs in a layered van der Waals GaS semiconductor. The EPR spectra of Mn2+ pairs (Mn24+) [replacing covalently bonded Ga24+ pairs oriented along the chain axis (c axis) of two gallium ions and being situated in the center of the layer] were recorded at 94 and 130 GHz. The fine structure parameters for the lower multiplets with spin S = 5 and S = 4 were determined equal to D = −0.040 cm−1 and D ≅ −0.035 cm−1, respectively. Based on the observation of additional EPR lines in the region of intersection of the levels in the magnetic field of the multiplet with S = 5 and S = 4, the energy of the isotropic exchange interaction J was estimated to be ∼−0.5 cm−1. For all transitions, a well-resolved hyperfine structure was observed, due to the interaction with two equivalent 55Mn nuclei, leading to the appearance of 11 lines with a hyperfine interaction constant A = 30(1) × 10−4 cm−1, which is approximately half the hyperfine interaction constant for single Mn2+ ions. In addition, a signal from single manganese ions Mn2+ with spin S = 5/2 and a hyperfine interaction constant A = 60(1) × 10−4 cm−1 was observed, which are characterized by extremely large fine structure splitting of D = −0.15 cm−1. Simultaneously with EPR studies, the crystals were monitored by photoluminescence and micro-Raman scattering measurements using a microscope with confocal optics.

MEPROS – Modular electron paramagnetic resonance operating software for multifunctional high-frequency EPR spectrometer

We present a software solution developed in LabVIEW for a home-built High–Frequency Electron Paramagnetic Resonance (HF-EPR) spectrometer. A modular approach was applied to control the spectrometer subsystems and simplify the adaptation to hardware changes during the development. The solution implements measuring procedures for conventional Continuous Wave EPR (CW-EPR), Frequency–Swept EPR (FS-EPR), and Two-Dimensional EPR (2D-EPR) mapping, which are relevant in different cases. The software’s automation capabilities were tested in several trial measurements to obtain CW-EPR spectra of Silicon Carbide doped by vanadium (SiC + V) at various temperatures and microwave frequencies, multi-frequency spectra via 2D-EPR mapping, and dense FS-EPR data of a lithium phthalocyanine crystal rotated in a magnetic field. Several prospective modifications of the software are discussed in the conclusion. A modular character allows the easy re-use of code portions in other experimental setups. The spectrometer and the software are currently deployed and utilized in a laboratory of EPR spectroscopy at Central European Institute of Technology (CEITEC) in Brno, and data obtained by it has been already used in a number of publications.

K2Mn3O(OH)(VO4)(V2O7) with Sawtooth Chains of Multivalent Manganese Triangular Trimer Units: Magnetic Susceptibility Shrouding a Long-Range Antiferromagnetic Order of Ferromagnetic Triangles.

ortho-Pyrovanadate (or ortho-diorthovanadate) K2Mn23+Mn2+O(OH)(VO4)(V2O7) synthesized hydrothermally crystallizes in the orthorhombic space group Pnma with a = 17.9155(5), b = 5.8940(2), c = 10.9971(3) Å, V = 1161.23(6) Å3, and Z = 4. Its crystal structure features linear chains of edge-sharing Mn3+O6 octahedra with every second pair of Mn3+O6 octahedra condensed with a Mn2+O6 octahedron on one side of a chain in a sawtooth pattern so that each sawtooth chain consists of a triangular trimer. These sawtooth chains, running parallel to the b axis and linked by the VO4 and V2O7 groups, form a framework with channels populated by K atoms. The new compound is a structural analogue of the mineral zoisite Ca2Al3O(OH)(SiO4)(Si2O7), showing a striking example of very different chemical compositions. K2Mn3O(OH)(VO4)(V2O7) undergoes a phase transition into an ordered antiferromagnetic (AFM) state at TN = 14.4 K, which was detected by high-frequency electron spin resonance as well as by both specific heat Cp and Fisher's specific heat d(χT)/dT measurements. However, this phase transition was not detected by magnetic susceptibility measurements. The origin of this puzzling observation was resolved by evaluating the spin exchanges of K2Mn3O(OH)(VO4)(V2O7), which revealed that each triangular trimer is a ferromagnetically coupled cluster, and the observed ordering involves an AFM ordering between the ferromagnetic (FM) clusters. This ordering is shrouded in magnetic susceptibility measurements due to the susceptibility contributions from the individual FM triangular trimers even below TN. We showed that the magnetic susceptibility of K2Mn3O(OH)(VO4)(V2O7) between ∼30 K and room temperature is satisfactorily described by an AFM chain made up of ferromagnetically coupled triangular clusters, as described by a few spin-exchange parameters.

Experimental Studies of Dzyaloshinskii–Moriya Interaction in Quantum Spin Systems: High-frequency High-field Electron Spin Resonance (ESR) Measurements

In this review, the importance of the Dzyaloshinskii–Moriya Interaction (DMI) to the magnetic properties of quantum spin systems is discussed mainly focusing on the determination of or understanding the role of DMI extracted from high-frequency high-field electron spin resonance (ESR) measurements. This review includes the ESR theories of the S = 1/2 one-dimensional (1D) antiferromagnet with the staggered field (Oshikawa–Affleck theory) and with the uniform DMI, and several related experimental results are shown. Then, the proposed mechanisms of the singlet–triplet transition in quantum spin systems together with the ESR selection rules are introduced in connection with various experimental results. Finally, the role of DMI in the ground state of kagome lattice antiferromagnets and the honeycomb lattice antiferromagnet is discussed with some experimental results.

Synergy of Magnetic Anisotropy and Ferromagnetic Interaction Triggering a Dimeric Cr(II) Zero-Field Single-Molecule Magnet

A novel CrII-dimeric complex, [CrIIN(SiiPr3)2(μ-Cl)(THF)]2 (1), has been successfully constructed using a bulky silyl-amide ligand. Single-crystal structure analysis reveals that complex 1 exhibits a binuclear motif, with a Cr2Cl2 rhombus core, where two equivalent tetra-coordinate CrII centers in the centrosymmetric unit display quasi-square planar geometry. The crystal structure has been well simulated and explored by density functional theory calculations. The axial zero-field splitting parameter (D < 0) with a small rhombic (E) value is unambiguously determined by systematic investigations of magnetic measurements, high-frequency electron paramagnetic resonance spectroscopy, and ab initio calculations. Remarkably, ac magnetic susceptibility data unveil that 1 features slow dynamic magnetic relaxation typical of single-molecule magnet behavior with Ueff = 22 K in the absence of a dc field. This increases up to 35 K under a corresponding static field. Moreover, magnetic studies and theoretical calculations point out that a non-negligible ferromagnetic coupling (FMC) exists in the dimeric Cr-Cr units of 1. The coexistence of magnetic anisotropy and FMC contributes to the first case of CrII-based single-molecule magnets (SMMs) under zero dc field.

High-Frequency EPR and ENDOR Spectroscopy of Mn2+ Ions in CdSe/CdMnS Nanoplatelets.

Semiconductor colloidal nanoplatelets based of CdSe have excellent optical properties. Their magneto-optical and spin-dependent properties can be greatly modified by implementing magnetic Mn2+ ions, using concepts well established for diluted magnetic semiconductors. A variety of magnetic resonance techniques based on high-frequency (94 GHz) electron paramagnetic resonance in continuous wave and pulsed mode were used to get detailed information on the spin structure and spin dynamics of Mn2+ ions in core/shell CdSe/(Cd,Mn)S nanoplatelets. We observed two sets of resonances assigned to the Mn2+ ions inside the shell and at the nanoplatelet surface. The surface Mn demonstrates a considerably longer spin dynamics than the inner Mn due to lower amount of surrounding Mn2+ ions. The interaction between surface Mn2+ ions and 1H nuclei belonging to oleic acid ligands is measured by means of electron nuclear double resonance. This allowed us to estimate the distances between the Mn2+ ions and 1H nuclei, which equal to 0.31 ± 0.04, 0.44 ± 0.09, and more than 0.53 nm. This study shows that the Mn2+ ions can serve as atomic-size probes for studying the ligand attachment to the nanoplatelet surface.

Zero-Field Splitting in Cyclic Molecular Magnet {Cr8Y8}: A High-Frequency ESR Study

Cyclic 3d-4f molecular magnets have received considerable attention owing to their potential applications in high-density data storage and quantum information processing. As a rare example of ferromagnetic polynuclear Cr rings, {Cr8Y8} represents a valuable test bed to directly study the magnetic interaction between Cr3+ ions in large hexadecametallic {Cr8Ln8} (Ln = 4f metal) molecules. We have proposed a “single-J” model to approximate the low-temperature spin dynamics of {Cr8Y8} in our earlier study, while a zero-field splitting (ZFS) of the quantum levels was also suggested by the heat capacity data. In order to have a deeper understanding of the magnetism of {Cr8Y8}, it is necessary to verify the ZFS by means of high-resolution spectral methods and identify its origin. In this work, we present a high-frequency electron spin resonance (HF-ESR) study on the ZFS of {Cr8Y8}. The X-band ESR spectra consists of multi-peak structure, indicative of magnetic anisotropy that breaks the degeneracy between spin states in the absence of a magnetic field. HF-ESR spectra are collected to extract the ZFS parameters. We observed a sharp resonance peak due to the transitions between the S = 11 quantum levels and a broadband corresponding to a distribution of resonance peaks due to the ZFS of the S = 12 quantum levels. By analyzing HF-ESR spectra, we confirm the expected S = 12 ground state and determine its ZFS parameter D as −0.069 K, and, furthermore, we reproduce the spectra recorded at 154 GHz. The macrospin model proves to still be valid. The ZFS is attributed to the axial magnetic anisotropy, as found in some other Cr-based molecular wheels. The detailed HF-ESR investigation presented in this paper will benefit the studies on other {Cr8Ln8} wheels with magnetic Ln3+ ions and highlights the importance of the HF-ESR method as a high-resolution probe in determining the ZFS parameters with very small magnitude.

Tetracoordinate Co(II) complexes with semi-coordination as stable single-ion magnets for deposition on graphene.

We present a theoretical and experimental study of two tetracoordinate Co(II)-based complexes with semi-coordination interactions, i.e., non-covalent interactions involving the central atom. We argue that such interactions enhance the thermal and structural stability of the compounds, making them appropriate for deposition on substrates, as demonstrated by their successful deposition on graphene. DC magnetometry and high-frequency electron spin resonance (HF-ESR) experiments revealed an axial magnetic anisotropy and weak intermolecular antiferromagnetic coupling in both compounds, supported by theoretical predictions from complete active space self-consistent field calculations complemented by N-electron valence state second-order perturbation theory (CASSCF-NEVPT2), and broken-symmetry density functional theory (BS-DFT). AC magnetometry demonstrated that the compounds are field-induced single-ion magnets (SIMs) at applied static magnetic fields, with slow relaxation of magnetization governed by a combination of quantum tunneling, Orbach, and direct relaxation mechanisms. The structural stability under ambient conditions and after deposition was confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Theoretical modeling by DFT of different configurations of these systems on graphene revealed n-type doping of graphene originating from electron transfer from the deposited molecules, confirmed by electrical transport measurements and Raman spectroscopy.

Unveiling the atomistic and electronic structure of NiII-NO adduct in a MOF-based catalyst by EPR spectroscopy and quantum chemical modelling.

The nature of the chemical bonding between NO and open-shell NiII ions docked in a metal-organic framework is fully characterized by EPR spectroscopy and computational methods. High-frequency EPR experiments reveal the presence of unsaturated NiII ions displaying five-fold coordination. Upon NO adsorption, in conjunction with advanced EPR methodologies and DFT/CASSCF modelling, the covalency of the metal-NO and metal-framework bonds is directly quantified. This enables unravelling the complex electronic structure of NiII-NO species and retrieving their microscopic structure.

Role of magnetoelastic coupling and magnetic anisotropy in MnTiO3

We report the thermodynamic properties studied by thermal expansion, magnetostriction, magnetisation, and specific heat measurements as well as the low-energy magnetic excitations of \mto\ and investigate how magneto-elastic coupling and magnetic anisotropy affect the evolution of long-range order and the magnetic phase diagram. Specifically, we utilise high-resolution capacitance dilatometry and antiferromagnetic resonance (AFMR) studies by means of high-frequency electron spin resonance (HF-ESR) spectroscopy. The role of anisotropy is reflected by spin-reorientation at $B_{\rm{SF}}$~$\simeq 6$~T and a corresponding sign change in $\partial T_{\rm N}/\partial B$. Analysis of the AFMR modes enables us to establish the zero-field excitation gap $\Delta$ as well as its temperature dependence. We derive the effective anisotropy field $B_\mathrm{A} = 0.16(1)$~T which predominately originates from out-of-plane nearest-neighbour dipole-dipole interactions. Despite the nearly fully quenched orbital moment, our data show pronounced thermal expansion and magnetostriction anomalies at $T_{\rm N}$ and $B_{\rm{SF}}$ , respectively, which allows the experimental determination of sizable uniaxial pressure dependencies, i.e., $\partial B_{\rm SF}/\partial p_{\rm c} = -0.20(2)$~T/GPa, $\partial T_{\rm N}/ \partial p_b = 0.69(12)$~K/GPa, and $\partial T_{\rm N}/ \partial p_c = -2.0(4)$~K/GPa. Notably, short-range magnetic order appears up to at least 3$T_{\rm N}$ , as indicated by anisotropic lattice distortion, the violation of a constant Gr\"uneisen behavior, and the presence of local magnetic fields detected by HF-ESR.

Non-Kramers iron S = 2 ions in β-Ga2O3 crystals: High-frequency low-temperature EPR study

Using high-frequency electron paramagnetic resonance (EPR), we have observed non-Kramers ions with giant fine structure splitting of the order of 100 GHz in n-type β-Ga2O3 crystals. These EPR spectra were assigned to Fe2+ ions 5D (3d 6) with S = 2. This interpretation was supported by experiments on Fermi level displacement induced by high-energy electron irradiation and photoexcitation of irradiated samples with 405-nm laser light. The values and signs of the basic parameters of the spin Hamiltonian for ions, namely Cr3+ (S = 3/2) and Fe3+ (S = 5/2), were identified, and the order of their spin levels was established.

Light and spins in rare-earth doped garnets

Spin-dependent optical properties of garnet crystals and garnet based ceramics, doped with cerium and also, along with cerium, co-doped with gadolinium and/or terbium, were studied by the method of optically detected of magnetic resonance by monitoring luminescence. The intensity of photoluminescence excited by circularly polarized light in the absorption bands of Ce3+ proved to be useful for selective monitoring of the population of the spin sublevels of the Ce3+ ground state. It was shown that due to cross-relaxation between the cerium and gadolinium electron spin systems the intensity of Ce3+ emission can be used to detect magnetic resonance of Gd3+. High-frequency EPR allowed finding a family of non-Kramers Tb3+ centers in yttrium aluminum garnet crystals. The influence of the magnetic resonance of Tb3+ on the luminescence of Ce3+ was observed. This suggests a coupling between the Tb3+ and Ce3+ systems, which are promising for coherent information processing. In irradiated crystals and ceramics of cerium-doped gadolinium-gallium garnet, magnetic field stimulation of the recombination of radiation defects was found, that is, it was shown that the energy accumulated during irradiation can be released in an external magnetic field. A huge increase in the afterglow intensity in a magnetic field and magnetic memory effects of magnetic memory were explained by the influence of strong internal magnetic fields on spin-dependent recombination.

High-Frequency EPR Studies of New 2p-3d Complexes Based on a Triazolyl-Substituted Nitronyl Nitroxide Radical: The Role of Exchange Anisotropy in a Cu-Radical System.

Using the 1-(m-tolyl)-1H-1,2,3-triazole-4-(4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) (TlTrzNIT) radical and metal β-diketonate complexes [M(hfac)2(H2O)2], where hfac is hexafluoroacetylacetonato, three new 2p-3d heterospin complexes were synthesized. Their structures were solved using single crystal X-ray diffraction data, and magnetic investigation was performed by DC and AC measurements and multifrequency EPR spectroscopy. Compounds 1 and 2 are isostructural complexes with molecular formula [M3(TlTrzNIT)2(hfac)6] (MII = Mn or Cu) while compound 3 is the mononuclear [Co(TlTrzNIT)(hfac)2] complex. In all complexes, the radical acts as a bidentate ligand through the oxygen atom of the nitroxide moiety and the nitrogen atom from the triazole group. Furthermore, in compounds 1 and 2, the TlTrzNIT is bridge-coordinated between two metal centers, leading to the formation of trinuclear complexes. The fitting of the static magnetic behavior reveals antiferromagnetic and ferromagnetic intramolecular interactions for complexes 1 and 2, respectively. The EPR spectra of 1 are well described by an isolated ferrimagnetic S = 13/2 (= 5/2 - 1/2 + 5/2 - 1/2 + 5/2) ground state with a biaxial zero-field splitting (ZFS) interaction characterized, respectively, by 2nd order axial and rhombic parameters, D and E, such that E/D is close to the maximum of 0.33. Meanwhile, EPR spectra for 2 are explained in terms of a ferromagnetic model with weakly anisotropic Cu-radical exchange interactions, giving rise to an isolated S = 5/2 (= 5 × 1/2) ground state with both an anisotropic g tensor and a weak ZFS interaction. Complex 2 represents one of only a few examples of Cu-radical moieties with measurable exchange anisotropy.

Tuning of Cr-Cr Magnetic Exchange through Chalcogenide Linkers in Cr2 Molecular Dimers.

A set of three Cr-dimer compounds, Cr2Q2(en)4X2 (Q: S, Se; X: Br, Cl; en: ethylenediamine), with monoatomic chalcogenide bridges have been synthesized via a single-step solvothermal route. Chalcogenide linkers mediate magnetic exchange between Cr3+ centers, while bidentate ethylenediamine ligands complete the distorted octahedral coordination of Cr centers. Unlike the compounds previously reported, none of the chalcogenide atoms are connected to extra ligands. Magnetic susceptibility studies indicate antiferromagnetic coupling between Cr3+ centers, which are moderate in Cr2Se2(en)4X2 and stronger in Cr2S2(en)4Cl2. Fitting the magnetic data requires a biquadratic exchange term. High-frequency EPR spectra showing characteristic signals due to coupled S = 1 spin states could be interpreted in terms of the "giant spin" Hamiltonian. A fourth compound, Cr2Se8(en)4, has a single diatomic Se bridge connecting the two Cr3+ centers and shows weak ferromagnetic exchange interactions. This work demonstrates the tunability in strength and type of exchange interactions between metal centers by manipulating the interatomic distances and number of bridging chalcogenide linkers.

High-frequency EPR spectroscopy of paramagnetic manganese centers in GaAs : Mn crystals

High-frequency electron paramagnetic resonance (EPR) is used to study the unique properties of manganese centers in a GaAs : Mn crystal in strong magnetic fields at low temperatures. At frequencies of 94 and 130 GHz, EPR transitions were recorded in the MnGa2+-SH complex, which is a manganese ion with spin S=5/2, which replaces gallium (MnGa2+) and an ionized acceptor (A-) associated via an isotropic antiferromagnetic exchange interaction with a shallow hole (SH) with angular momentum J=3/2. A complex system of energy levels of this complex in a magnetic field and the possibility of accurately determining exchange interactions from EPR spectra are analyzed. Another complex was investigated, in which an ionized acceptor MnGa2+ interacts with a localized hole center in the form of a diamagnetic ion O2- replacing As. This complex, MnGa2+-OAs2-, is characterized by axial symmetry along the &amp;lt;111&amp;gt; axis of the cubic GaAs crystal and an anisotropic EPR spectrum. Due to the high Boltzmann factor, in our studies, the order of the fine structure spin levels of this complex was determined. The effect of the Boltzmann populations of the energy levels on the high-frequency EPR spectra was also demonstrated for the MnGa2+-SH complex. Keywords: high-frequency EPR, GaAs crystal, Mn acceptor, shallow hole, exchange interaction.

High-frequency EPR spectroscopy of paramagnetic manganese centers in GaAs : Mn crystals

High-frequency electron paramagnetic resonance (EPR) is used to study the unique properties of manganese centers in a GaAs : Mn crystal in strong magnetic fields at low temperatures. At frequencies of 94 and 130 GHz, EPR transitions were recorded in the MnGa2+-SH complex, which is a manganese ion with spin S=5/2, which replaces gallium (MnGa2+) and an ionized acceptor (A-) associated via an isotropic antiferromagnetic exchange interaction with a shallow hole (SH) with angular momentum J=3/2. A complex system of energy levels of this complex in a magnetic field and the possibility of accurately determining exchange interactions from EPR spectra are analyzed. Another complex was investigated, in which an ionized acceptor MnGa2+ interacts with a localized hole center in the form of a diamagnetic ion O2- replacing As. This complex, MnGa2+-OAs2-, is characterized by axial symmetry along the &lt;111&gt; axis of the cubic GaAs crystal and an anisotropic EPR spectrum. Due to the high Boltzmann factor, in our studies, the order of the fine structure spin levels of this complex was determined. The effect of the Boltzmann populations of the energy levels on the high-frequency EPR spectra was also demonstrated for the MnGa2+-SH complex. Keywords: high-frequency EPR, GaAs crystal, Mn acceptor, shallow hole, exchange interaction.

Sample Holders for Sub-THz Electron Spin Resonance Spectroscopy

Electron spin resonance (ESR) is a powerful spectroscopic technique used to investigate samples with unpaired electrons in a broad range of scientific fields. High-frequency ESR (HF-ESR) spectrometers operating at sub-THz frequencies are mostly custom-made with non-standard solutions. This article presents a set of six different exchangeable sample holders with a fast-loading flange for a sub-THz ESR spectrometer operating at high magnetic fields up to 16 T and temperature ranges of 4–400 K. Here, we report on the concept, design, and illustrative measurements of non-resonant ESR sample holders for the measurements of samples in a liquid solution, polycrystalline-compressed powders, oriented single crystals, electrical devices under sub-THz irradiation, as well as for samples transferred from the ultrahigh vacuum (UHV) systems without air contamination. Our solution expands the usage possibilities for HF-ESR spectroscopy, showing that one spectrometer with the presented concept of sample holders enables a wide range of applications.