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Three temperature-induced phase transitions at T=T1, TM/TA, and TC, related to the ferromagnetic order of the martensitic phase (FMMP), martensitic (structural) transitions (MT), and the ferromagnetic order of the austenitic phase (FMAP), respectively, have been observed in the off-stoichiometric Heusler alloys, Ni50-xCoxMn35In15 (x=1, 2.5) and Ni45Co5Mn37In13. The phase transitions temperatures are found to be depended on alloy composition. A kinetic arrest of the AP was observed for Ni47.5Co2.5Mn35In15 in the magnetization measurements during field-cooling cycle (FCC) at 50 kOe. Depending upon the cooling protocols, ZFC and FCC (at H = 50 kOe), two different ground states of the alloys can be found in Ni47.5Co2.5Mn35In15 and Ni45Co5Mn37In13 alloys. The ground states (T=4.2 K and external field H=0) of the alloys was found to be characterized by three main line: two, partially overlapping, at higher frequencies (300-450 MHz), most likely corresponding of manganese resonance lines and one at lower frequency at about 200 MHz. A significant shift in the spectrum of Ni45Co5Mn37In13 by about 100 MHz to higher frequencies was observed. The correlation of magnetizations obtained from magnetic moment and NMR studies is discussed.

A combined XRD, Mössbauer, SEM, STXM and NMR study of naturally oxidised, ball milled iron powders is presented. The XRD patterns show the peaks of the bcc-Fe phase with the line widths increasing with the milling time. This corresponds to a flattening of the crystallites, as confirmed by SEM, and increased strain due to the accumulation of defects. The effect is consistent with the variation of the Mössbauer line-widths with the milling time. Scanning Transmission Xray Microscopy (STXM) measurements provided oxygen maps of the particles and revealed that the dominant oxide in the nanometric oxide layer is magnetite. The 57Fe spin echo NMR study reveals a dominant signal corresponding to a bcc-Fe core and a much weaker resonance corresponding to a magnetite amount of less than 1%.

While investigating the Fe-rich part of the pseudo-binary system SrO—Fe2O3, the well-known M-type SrFe12O19 (I) and two additional ferrites, W-type SrFeII2FeIII16O27 (II) and X-type Sr2FeII2FeIII28 O46 (III) are found at high temperatures from calcined and sintered mixtures of SrCO3 and Fe2O3 (1200 °C for (I); 1370 °C for (III); 1400 °C for (II), all 24 h).

NMR spectra on 57 Fe nuclei in yttrium iron garnet (YIG) containing Y 3+ (a) defects and Al 3+ (d) substitutions were measured in the temperature range 4.2–360 K in zero external magnetic field. The temperature dependencies of satellite lines caused by Y 3+ (a), Al 3+ (d) impurities were determined. Theoretical description of the temperature behavior of the main and satellite lines has been carried out in the frame of model based on the Bethe–Peierls–Weiss approximation.

Magnetite single crystals with Al, Ga and Ti substitutions were measured by means of 57Fe nuclear magnetic resonance (NMR) technique. Satellite structure of NMR spectra well above the Verwey temperature was detected and analyzed to obtain information on the distribution of substituting cations on iron sublattices. It was confirmed that Al and Ti enter iron octahedral B-sites. Ga strongly prefers tetrahedral A-sites, nevertheless a low presence of Ga cations in B-sites was detected.

We report the NMR spectra of gallium substituted magnetite measured at temperatures 4.2, 77 and 273 K. A single crystal of Fe 3− x Ga x O 4 , x = 0.05 has been prepared by a floating zone technique. The Ga-lines found in the NMR spectrum above Verwey temperature T V ∼ 117 K indicate a preferency of Ga substitution into the tetrahedral A-sites. The well-resolved structure of Ga-lines has been identified and assigned to both Ga isotopes below T V . A weak quadrupolar interaction contributes only to the line broadening.

NMR of 57 Fe nuclei is used to study the Y antisite defects (yttrium ions on the sites nominally occupied by iron) in yttrium-iron garnet (YIG). In spectra of both tetrahedral and octahedral Fe 3+ ions, satellite lines appear, corresponding to Fe 3+ ions with this defect in their vicinity. NMR was measured on a number of nominally pure YIG samples - single crystals, thin films as well as polycrystalline samples. The content X Y per formula unit of the Y antisite defect (Y a ) was determined from the amplitude of the satellite lines and it lies in the interval 0.001< x y < 0.03. In most cases the satellite lines caused by the Y a defect are obscured by the satellites originating from other impurities. In two high purity single crystals the satellites caused by Y a dominate, however. In the NMR spectra of these single crystals the satellite lines which correspond to the Felt ions in seven different crystallographically inequivalent positions with respect to the defect are resolved at low temperatures. Further unresolved satellites emerge from the main lines as the temperature is increased.

The dependence of 57 Fe NMR spectra in YIG on the external magnetic field direction was measured at 4.2K. The high purity single crystal of a spherical form was used. The external magnetic field of 0.75T was applied in several directions lying in (110) plane. The satellite structure of the spectra caused by an antisite defects Y(a) (Y 3+ ion on the a site, nominally occupied by Fe 3+ ion) enabled us to study the effect of a nonmagnetic impurity on the 57 Fe hyperfine field anisotropy. The tensors of hyperfine interaction for 57 Fe in d- sites with the nearest and next nearest Y(a) defect were obtained from NMR data. The results were confronted with the predictions of the independent bond model.

Temperature dependence of 57 Fe NMR spectra was measured below and around the Verwey transition in Fe 3− x Al x O 4 ( x =0, 0.005, 0.01, 0.02, 0.03) single crystals. All lines of substituted samples were broadened with increasing Al concentration, but we have found no change in their positions. The Verwey temperature T V decreases with increasing Al concentration in agreement with electric conductivity measurements. The satellite structure found in the vicinity of the A-line above T V disappears below T V , on the other hand a broad spectrum in the spectral region 35–45 MHz at temperature 4.2 K was detected.

The easy magnetic axis switching in magnetite is investigated. Magnetization data confirmed activation character of the process with activation energy of the same order as that of the Verwey transition, suggesting common origin. On the other hand this activation energy rises with pressure (up to 1.2GPa), unlike TV. The axis switching is clearly reflected in field dependence of resistivity and the direct structural data showed that it is simultaneous with the reorganization of structure. Thus, control of the structure can be possible with the application of magnetic field, as in shape memory materials. Finally, NMR showed that all, possibly decoupled entities: lattice distortion and charge and orbital orderings, change simultaneously while the axis switching occurs.

NMR on ${}^{57}\mathrm{Fe}$ nuclei was measured in two single crystals of magnetite between 4.2 and 135 K (temperature of the Verwey transition ${T}_{V}=121.5$ and 123.9 K). We were able to register all lines detected at 4.2 K also at higher temperatures up to ${T}_{V}.$ The spectra are compatible with the space group $Cc,$ which predicts 8 and 16 lines for iron on tetrahedral (A) and octahedral (B) sites, respectively. One of the $\mathrm{Fe}(A)$ lines is doubly degenerate for all $Tl{T}_{V},$ which restricts the possible models of the ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ ordering on the B sites. Above ${T}_{V}$ no remnant of the low-temperature spectrum was detected. At 4.2 K the NMR spin-spin and spin-lattice relaxation times were determined.

The NMR spectra of 57 Fe in Pr:YIG, Nd:YIG and Yb:YIG were measured on polycrystalline samples at 4.2 K in the zero external field. In the NMR spectra of both tetrahedral and octahedral sites the resolved satellite structure appears. This structure is caused by the change of the hyperfine field on the nuclei of those Fe 3+ ions, which are the nearest or next nearest neighbours of the substituted Re 3+ ion. The change of the hyperfine field is given by the change of dipole and transferred contribution. Both contributions are sensitive to the kind of Re 3+ ion and to the value and direction of its magnetic moment. The satellite structure of NMR spectra provides sufficient amount of information (splitting) to find unknown parameters of the non-collinear (umbrella) arrangement of Re 3+ magnetic moments.