Single Fe impurities were implanted in an Er single crystal and found to occupy both substitutional and interstitial sites, below a temperature of 200 K. The local susceptibility of Fe on both sites follows a Curie–Weiss law and exhibits a positive local Curie constant, indicating an antiferromagnetic coupling between the Fe and the surrounding Er moments. The corresponding nuclear spin relaxation rates follow a Korringa law as a function of temperature, confirming the dominance of local magnetism and the formation of local moments on each of the sites occupied by Fe.

The magnetization-reversal processes of ferromagnetic Co in [Co/CoO/Au]20 exchange-bias multilayers are studied with polarized neutron reflectometry. The investigations were performed at 300 K, i.e. above the Néel temperature of CoO. We measured the non-spin-flip as well as the spin-flip intensities. Thus, we are able to distinguish between a magnetization rotation and a domain-wall movement. This is essential, in order to compare the obtained results to measurements performed below TN of CoO, when the sample is in the exchange-bias state (i.e. after field cooling).

Low temperature nuclear orientation has been used for the first time to investigate the magnetization reversal processes in an exchange bias system (Co/Au/CoO), with the advantage of observing both the Co and Au layers at the same time. By monitoring the counting-rate ratio of two γ-ray detectors, the measurements may be used to distinguish between reversal processes dominated by domain wall motion as opposed to rotation of the magnetization.

A drastic change of magnetization reversal processes in $[\mathrm{C}\mathrm{o}/\mathrm{C}\mathrm{o}\mathrm{O}/\mathrm{A}\mathrm{u}{]}_{20}$ multilayers has been found by polarized neutron reflectometry. For the unbiased state $(T=300 \mathrm{K}),$ reversal is due to rotation on both sides of the hysteresis loop. In the exchange-bias state $(T=10 \mathrm{K}),$ rotation is the main mechanism only for increasing fields. For the decreasing field branch, which is in the direction opposite to the bias (cooling field), the mechanism changes to domain-wall motion. A major advantage of the present CoO/Co system is the independence of exchange bias on cooling field orientation.

We used the in-beam TD perturbed angular distribution (PAD) technique to investigate the magnetism and lattice location of dilute impurities of Sc and Fe implanted into single-crystal Gd and Tb host lattices. Sc is observed to implant on a unique site, which is almost certainly substitutional. The T = 0 hyperfine field Bhf(0) is found to be −5.22(1) T in Gd host and −3.91(3) T in Tb host, both values being corrected for demagnetizing and Lorentz fields. At higher temperatures, the hyperfine fields deviate from the host lattice magnetization M(B,T); the local susceptibilities however follow Curie-Weiss laws similar to those of the hosts. Fe is found to implant onto two lattice sites, which can be identified by comparison with the similar host Y as substitutional and interstitial sites. The hyperfine fields are small and positive on both sites, but distinctly larger on the substitutional site. Again, Curie-Weiss behavior is found for the local susceptibilities up to 500 K in both hosts. Fe signals are unobservable below TC, probably owing to line broadening.

Implanted Fe atoms in hcp Zr, Ti, and Hf occupy both substitutional and interstitial lattice sites. In all three systems, substitutional Fe is found to be strongly magnetic, while interstitial Fe is nonmagnetic. First principles calculations for the magnetic properties and the isomer shift have been carried out for substitutional sites (by two independent methods) and for the interstitial sites. The theoretical predictions for both lattice sites are in excellent agreement with the experimental results.

Using perturbed γ-ray distribution techniques and in-beam Mössbauer spectroscopy, the magnetism, electronic structure, and lattice sites of Fe ions implanted into Y have been investigated. About 65% of the Fe atoms occupy interstitial sites, which come out to be non-magnetic. The remaining fractions is found on substitutional sites, and exhibits a nearly Curie-type susceptibility and Korringa-type spin dynamics. Local spin density calculations predict the magnetic moment, the hyperfine field and the isomer shift in agreement with the experimental results.

The local susceptibility of isolated Mo ions in Na is observed to be consistent with a localized, magnetic 4${d}^{5}$ state of ${\mathrm{Mo}}^{1+}$. Size, valence, and bonds of such ${\mathrm{Mo}}^{1+}$ cells are similar to the host ${\mathrm{Na}}^{1+}$ cells. These features allow a study of 4d magnetism by local-spin-density calculations under the premise of substitutional Mo ions in Na. The calculations yield an effective moment of more than 5${\ensuremath{\mu}}_{B}$ for Mo in Na. In the larger hosts, K, Rb, and Cs, we propose unusual large lattice contractions around d ions with localized d states, up to 22% for the extreme case of ${\mathrm{Fe}}^{2+}$ in Cs. This results from impurity-host bond strengths larger than those between host atoms along with the very large compressibilities of K, Rb, and Cs.

By applying the perturbed-\ensuremath{\gamma}-ray-distribution method following heavy-ion reactions we have observed strong magnetic moments for isolated Fe ions in solid and liquid Hg reflecting a Curie-type local susceptibility along with a small Fe spin-fluctuation rate. The magnetism of Fe ions in Hg exhibits qualitative differences to the behavior of Fe in sp band metal hosts but is strikingly similar to the magnetism of Fe in hosts with d- band electrons, including Cu, Ag, and Au. We propose that the interaction of Fe 3d with Hg 5d band electrons is crucial for the existence and stability of Fe moments in Hg.

Mainly based on data for local susceptibilities and $3d$ spin rates of dilute Fe ions in many metals, we conclude that the existence and stability of Fe, Co, and Ni moments in Cu, Ag, Au, and certain transition-metal hosts are governed by impurity-$3d$ host-$d$ electron interactions. As the leading contribution to moment stability we propose ferromagnetic-$3d$ host-$d$ exchanges which in certain hosts successfully suppress spin fluctuations arising from antiferromagnetic $d\ensuremath{-}sp$ exchanges. All host-dependent trends of moment stability of Mn, Fe, Co, and Ni ions in metals are consistent with our proposal.

We have explored the applicability of the perturbed γ-ray distribution method following heavy-ion reactions for microscopic investigations of magnetic properties of CuO and high-Tc materials. The spin rotation of dilute 18F and 19F ions recoil implanted into CuO is consistent with the onset of antiferromagnetic ordering at 225 K and with dynamic antiferromagnetic correlations above 225 K. The magnetic response of F ions in YBa2Cu3O ∼ 7 and La1.85Sr0.15CuO4 yields negligible frequency shifts and no measurable indication of antiferromagnetic order.

Spin and orbital magnetism of Fe ions in $\mathrm{sp}$ metals are reduced simultaneously from stable ionic ${\mathrm{Fe}}^{2+}$ to nonmagnetic behavior with increasing lattice pressure. The various data and interpretations of the host and temperature-dependent susceptibilities, of $3d$ spin dynamics, and of crystal fields of Fe ions in $\mathrm{sp}$ metals provide a new critical test of models on moment formation, $d\ensuremath{-}\mathrm{sp}$ exchanges, and the Kondo effect of $3d$ ions in $\mathrm{sp}$ metals. Fe in $\mathrm{sp}$ metals reflects basic features common to certain $4f$ systems, but with qualitative differences from the magnetism of Fe in noble metals.

The 3d spin dynamics and local susceptibility of isolated Fe ions recoil implanted into the high Tc superconductors YB2Cu3O7−δ and EuBa2Cu3O7−δ have been measured using the perturbed γ-ray distribution method. The observation of a Curie-type susceptibility and Korringa-type relaxation indicates a stable Fe moment in the superconductors with negligible orbital contributions. The observed 3d spin rate corresponds to an extremely small spin line-width of 0.5 meV at 300 K, which is consistent with a very weak coupling of the Fe spin to the host conduction electrons and with a weak pair breaking.

By application of the TDPAD method in connection with heavy ion reactions and recoil implantation techniques we have probed the magnetic behaviour of 4f and 3d and 4d transition metal ions under extreme variations of the chemical environment. New unstable 4f systems have been found by implanting the oversized 4f ions in small-volume hosts like e.g. W. The implantation of 3d and 4d ions into alkali metal hosts has led to the discovery of a series of anomalies, e.g. the magnetic behaviour of Fe ions in K, Rb and Cs is consistent with a completely localized 3d shell in spin orbit coupling along with a negligible crystal electrical field splitting and has led to the observation of strong local magnetism in 4d systems. The extreme cases of local magnetism have been found in non-alloying systems.

By application of the perturbed \ensuremath{\gamma}-ray distribution method following heavy-ion reactions, we have found an experimental method of producing and investigating strong local 4d magnetism in metals. Mo ions recoil implanted into alkali metals show a large local moment and an extremely small 4d spin-relaxation rate. The data along with an analysis using a Born-Haber cycle are consistent with a localized 4${d}^{5}$ shell behavior for isolated Mo ions in Rb and Cs.

The local susceptibility and $3d$-spin dynamics of isolated Fe ions recoil implanted into alkali-metal hosts is measured by the perturbed-$\ensuremath{\gamma}$-ray-distribution method. The observations of extremely large values for the hyperfine fields and magnetic moments and of an extremely small spin linewidth are quantitatively consistent with a stable $3{d}^{6}$ configuration of ${\mathrm{Fe}}^{2+}$ ions in spin-orbit coupling along with a negligible crystal-field splitting. Fe in Li strongly deviates from the magnetic behavior of a purely ionic configuration. The results permit a comparison of local-moment formation of $3d$ with $4f$ systems.

By application of the perturbed \ensuremath{\gamma}-ray distribution method in connection with heavy-ion reactions and recoil-implantation techniques, magnetic single-ion instabilities of Pr, Nd, and Pm ions in small-volume hosts like Ta, W, Os, and Ir have been found. The local susceptibilities observed in the instable Pr, Nd, and Pm systems are strongly reduced compared to both the stable ${3}^{+}$ and ${4}^{+}$ ion behaviors. The data indicate a strong 4f--conduction-electron hybridization as the common basic mechanism for the instabilities in Ce, Pr, Nd, and Pm systems.